Indian Patents. 271422:"NOVEL LIPOPHILIC ETHER DERIVATIVES OF DIHYDROARTEMISININ"

Title of Invention	"NOVEL LIPOPHILIC ETHER DERIVATIVES OF DIHYDROARTEMISININ"
Abstract	This invention relates to novel lipophilic ether derivatives of Dihydroartemisnin. The invention also relates to a process for preparation of the said compounds. The compounds of the present invention are useful as antimalarials.

Full Text	This invention relates to novel lipophilic ether derivatives of dihydroartemisinin. The invention also relates to a process for the preparation of the said compounds. The compounds of the present invention are useful as antimalarials. This invention generally relates to a process for the preparation of lipophilic ethers of dihydroartemisinin 2 of general formula 6 as a new series of antimalarials which are active by both i.m. and oral routes. More particularly the present invention relates to new ether derivatives of dihydroartemisinin of general formula 6 wherein R represent groups such as 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1 -Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl and the like. Some of these compounds are several times more potent than the current artemisinin-based antimalarials such as artemether 3 and arteether 4. Dihydroartemisinin is available from reduction of artemisinin 1, a natural product antimalarial from Artemisia annua. [For background literature on artemisinin and its derivatives see: (a) Klayman, D. L Science 1985, 228, 1049. (b) Bhattacharya, A. K.; Sharma, R. P. Heterocycles 1999, 51, 1651. (c) Borstnik, K.; Paik, I.; Shapiro, T. A.; Posner, G. H. Int. J. Parasitol. 2002, 32, 1661. (d) Ploypradith, P. Acta Trop. 2004, 89, 329. (e) O'Neill, P. M.; Posner, G. H. J. Med. Chem. 2004, 47, 2945.] The main objective of this invention is to provide novel lipophilic ether derivatives of dihydroartemisinin which are more potent antimalarials than the clinically useful ether derivatives of the dihydroartemisinin such as artemether and arteether. These compounds have been tested against multi-drug resistant Plasmodium yoelii in mice and have been found several times more active than artemether and arteether by oral route. Thus, the invention relates to pharmaceutical industry. Accordingly, the present invention provides novel lipophilic ether derivatives of dihydroartemisinin having the following formula 6 (Formula Removed) wherein, R is a biphenyl or adamantly group selected form 2-Biphenylmethyl, 4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl represented by the chemical formula 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j and 6k given here as under: (Formula Removed) The present invention also provides a process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin, wherein the process comprises: (Formula Removed) with lipophilic alcohols of general formula 5 represented as R-OH, wherein R represents 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl under acidic conditions at a temperature ranging from -10°C to 27°C in the presence of an acidic catalyst and organic solvent such as herein described; b] neutralization of the product obtained from step [a] with an organic solvent; c] washing the product obtained from step [b]; d] drying the washed product of step [c] by conventional methods; e] purifying the product obtained from step [d] to obtain the compound of formula 6. In an embodiment of the present invention the reaction of dihydroartemisinin of formula 2 with lipophilic alcohols of general formula 5 may be effected under acidic conditions using acidic catalysts such as BF3.OEt2, p-toluenesulphonic acid (PTSA), coned HCl, coned H2SO4, cation exchanger such as Amberlyst-15 and the like. In another embodiment of the invention the organic solvent used may be chosen such as CH2CI2, C6H6,CHCl3,THF etc. Purification of compounds of general formula 6 wherein R has the same meaning as above, may be carried out by column chromatography using combination of organic solvents as eluants. The products which are mixtures of a and (3 isomers can be further separated by column chromatography to give pure a- isomers of general formula 7 and ß- isomers of general formula 8 wherein R has the same meaning as above. (Formula Removed) ihydroartemisinin of formula 2 is prepared by reduction of artemisinin 1 by known process. The compounds of the general formula 6, 7, and 8 are new and have not been prepared earlier. This invention is further illustrated by the following examples which should not, however, be construed to limit the scope of the present invention. EXAMPLE 1 4-Biphenylmethyl ether of dihydroartemisinin [compound 6a,7a & 8a, formula 6, 7 and 8, R= 4-Biphenylmethyl] To a solution of dihydroartemisinin (1.5g, 5.28 mmol) and biphenyl-4-yl-methanol (l.Og, 5.43 mmol) in 50ml dichloromethane was added BF3.0Et2 (4 drops) at -10°C to -5°C. The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave pure 8a as a solid (1.26g, 53.2%); m.p. 49-510C, a mixture of 7a & 8a (0.23g, 9.7%) and pure 7a as a solid (0.18g, 7.6%); m.p.79-80°C (combined yield 70.5%). EXAMPLE 2 4-Biphenylethyl ether of dihydroartemisinin [compound 6b & 8b, formula 6, 7 and 8, R=4-biphenylethyl] To a solution of dihydroartemisinin (l.Og, 3.52mmol) and 4-biphenylethanol (700mg, 3.53 mmol) in 50ml dichloromethane was added BF3.0Et2 (4 drops) at -100C to -50C.The mixture was stirred at the same temperature for 24h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethyl acetate/hexane (3:97) as eluant gave pure 8b as a solid (1.34g, 82.2%); m.p.l 10-112°C. EXAMPLE 3 2-(biphenyl-4-yloxy) ethyl ether of dihydroartemisinin [compound 6c,7c & 8c, formula 6, 7 and 8, R=2-(biphenyl-4-yloxy) ethyl] To a solution of dihydroartemisinin (0.55g, 1.94mmol) and 2-(Biphenyl-4-yloxy)-ethanol (500mg, 2.33 mmol) in 40ml dichloromethane was added BF3.0Et2 (4 drops) at -100C to -50C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:24) as eluant gave pure 8c as a white solid (360mg, 38.7%); m.p. 111-112° C, a mixture of 7c & 8c (lOOmg, 10.7%) and pure 7c as a white solid (160mg, 17.2%); m.p.l08-109°C (combined yield 66.6%). Compound 7c & 8c was also prepared using different reaction conditions. Results are summarized in table 1. Table 1. (Table Removed) EXAMPLE 4 l-Adamantanemethyl ether of dihydroartemisinin (compound 6d, formula 6, R= 1-Adamantanemethyl) To a solution of dihydroartemisinin (900mg, 3.17mmol) and Adamantan-1-yl-methanol (585mg, 3.52 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for Ih. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave an inseparable 1:3 mixture of 6d as a white crystalline solid (1.24g, 91.1%); m.p. 146-147°C. EXAMPLE 5 2-Adamaiitanyl ether of dihydroartemisinin (compound 6e, formula 6, R=2-Adamantanyl) To a solution of dihydroartemisinin (800mg, 2.81mmol) and 2-adamantanol (535mg, 3.51 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C. The mixture was stirred at the same temperature for Ih. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave an inseparable 1:3 mixture of 6e as a white solid (1.43g, 96.5%); m.p. 136-138°C. EXAMPLE 6 2-(biphenyl-2-yloxy) ethyl ether of dihydroartemisinin [compound 6f,7f & 8f, formula 6, 7 and 8, R=2-(biphenyl-2-yloxy) ethyl] To a solution of dihydroartemisinin (800mg, 2.81mmol) and 2-(Biphenyl-4-yloxy)-ethanol (750mg, 3.5 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -10°C to -5'C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (3:97) as eluant gave pure 8f as a solid (740mg, 54.8%); m.p. 90-92°C, a mixture of 7f & 8f (230 mg, 17.0%) and pure 7f as a solid (300mg, 22.2%); m.p.l03-105°C (combined yield 94.0%). EXAMPLE 7 2-Biphenylmethyl ether of dihydroartemisinin (compound 6g & 8g, formula 6, 7 and 8, R=2- Biphenylmethyl) To a solution of dihydroartemisinin (800mg, 2.81mmol) and Biphenyl-2-yl-methanol (650mg, 3.53 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C. The mixture was stirred at the same temperature for 1.25h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave the mixture of a- and (3- isomers as a solid (1.13g, 96.5%) which on crystallization in CH2Cl2 /hexane gave pure 8g as a white crystalline solid (250mg, 21.3%); m.p. 130-132°C. EXAMPLE 8 2-(9H-fluoren-9-yl) - ethyl ether of dihydroartemisinin [compound 6h, formula 6, R= 2-(9H-nuoren-9-yl) - ethyl] To a solution of dihydroartemisinin (0.50g, 1.76mmol) and 2-(9H-fluoren-9-yl)- ethanol (0.55g , 2.62 mmol ) in 40ml dichloromethane was addedBF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for 3h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (3:97) as eluant gave an 1:4 mixture of 6h as a white solid (0.83g, 99.0%);m.p. 131-1330C. EXAMPLE 9 (9H-fluoren-9-yl)-methyl ether of dihydroartemisinin [compound 6i,7i & 8i, formula 6, 7 and 8, R= (9H-fluoren-9-yl) - methyl] To a solution of dihydroartemisinin (0.50g, 1.76mmol) and (9H-fluoren-9-yl)-methanol(0.51g, 2.60 mmol ) in 30ml dichloromethane was added BF3.OEt2 (4 drops) at -10°C to -5'C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25 ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethyl acetate / hexane (1:49) as eluant gave pure 7i as a white solid (O.lOg, 12.3%); m.p. 100-102°C, a mixture of 7i & 8i (0.09g, 11.0%) and pure 81 as a white solid (430 g, 52.8%); m.p.l36-138°C (combined yield 76.2%). EXAMPLE 10 2-adamamantan-l-yl-ethyl ether of dihydroartemisinin [compound 6j,7j & 8j, formula 6, 7 and 8, R= 2-adamantan-l-yl -ethyl] To a solution of dihydroartemisinin (l.0g, 3.52 mmol) and 2- adamantan-1-yl-ethanol (0.95g, 5.27 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for 9h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave 1:3 mixture of 7j & 8j (1.24g ,78.9%)) which on flash chromatography over flash silica gel using ethyl acetate/hexane (0.75:99.25) as eluant gave pure 8j as a white solid (0.29g , 18.4 %); m.p. 65-67 °C, a mixture of 7j & 8j (0.88g , 56.0%) and pure 7j as an oil (0.07g , 4.4%). EXAMPLE 11 2-adamantan-2-yl-ethyl ether of dihydroartemisinin [compound 6k, 7k & 8k, formula 6,7 and 8, R= 2-adamantan-2-yl -ethyl] To a solution of dihydroartemisinin (l.Og, 3.52 mmol) and 2-adamantan-2-yl-ethanol (0.950 g, 5.27 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -50C.The mixture was stirred at the same temperature for 9h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:99) as eluant gave 1:3 mixture of 7k & 8k (1.27g, 81.2%) which on flash chromatography over flash silica gel using ethylacetate/hexane (0.2:99.8) as eluant gave pure 8k as a solid (0.58 g, 36.9%); m.p. 50-52 °C, a mixture of 7k & 8k (0.586g, 37.3%) and pure 7k as a white solid (0.llg, 7.0%); m.p. 75-77°C (combined yield 81.2%). Following the above procedure the following lipophilic ether derivatives of dihydroartemisinin 6a,7a, 8a,6b, 8b, 6c,7c, 8c, 6d, 6e, 6f, 7f, 8f, 6g,8g, 6h, 6i,7i, 8i,6j, 7j, 8j,6k, 7k and 8k were prepared (scheme 1, table 2). Table 2 (Table Removed) [compound 6b & 8b, formula 6, 7 and 8, R=4- biphenylethyl] ~3^ 2-(biphenyl-4-yloxy) ethyl ether of 7c:108-109"C 66.6 dihydroartemisinin [compound 6c, 7c i& 8c, 8c:lll-112V formula 6, 7 and 8, R=2-(biphenyl-4-yloxy) ethyl] Z 1-Adamantanemethyl ether of 6d:146-147V 9U dihydroartemisinin (compound 6d, formula 6, R= 1-Adamantanemethyl) 5. 2-Adamaiitanyl ether of dihydroartemisinin 6e:136-138V 96.5 (compound 6e, formula 6, R=2-Adamantanyl) 6] 2-(biphenyl-2-yloxy) ethyl ether of 7f: 94.0 dihydroartemisinin [compound 6f,7f & 8f, 103-1050C formula 6, 7 and 8, R=2-(biphenyl-2-yloxy) 8f: ethyl] 90-92V 7. 2-Biphenylmethyl ether of dihydroartemisinin 8g: 96.5 (compound 6g & 8g, formula 6, 7 and 8, R=2- 130-132V Biphenyl methyl) 8. 2-(9H-fluoren-9-yl) ^ ethyl ether of 6h:131-133V 99.0 dihydroartemisinin [compound 6h, formula 6, R= 2-(9H-fluoren-9-yl) - ethyl] 9. (9H-fluoren-9-yl)-methyl ether of 7i; 762 dihydroartemisinin [compound 6i,7i & 8i, 100-102°C formula 6, 7 and 8, R= (9H-fluoren-9-yl) - 8i: methyl] 136-138°C 10. 2-adamantan-l-yl-ethyl ether of 8j: 78.9 dihydroartemisinin [compound 6j,7j & 8j, 65-67°C formula 6, 7 and 8, R= 2-adamantan-l-yl -ethyl] 11 2-adamantan-2-yl-ethyl ether of 7k: 81.2 dihydroartemisinin [compound 6k,7k & 8k, 75-77 °C formula 6,7 and 8, R= 2-adamantan-2-yl -ethyl] 8k: Antimalarial activity The blood schizontocidal activity of the test compounds was evaluated in rodent model using multi-drug resistant strain of Plasmodium yoelii nigeriensis in Swiss mice. General procedure Random bred Swiss mice of either sex (20 ± 2 g) were inoculated intraperitoneally with 1x105 P. yoelii (MDR) parasites on day zero. The treatments with test compounds were administered to group of 6 mice each at different dose levels ranging between 12-48 mg/kg/day. The compounds were administered as solutions in oil via oral route for 4 consecutive days (day 0-3). P-Arteether and a-Arteether was used as positive control. Blood smears from experimental mice were observed on day 4 and 7, day 10 and thereafter at regular interval till day 28 or death of the animal. The parasitaemia level on day 4 was compared with the vehicle control group and the percent suppression of parasitaemia in treated groups was calculated. The compounds which showed more than 90%suppression were identified for further screening. For determing the curative dose of a compound the treated mice were observed till day 28.The dose at which no parasitaemia develops during the observation period has been recorded as the curative dose. The results are shown in table 3. (Table Removed) Scheme 1 Reagents and conditions: (a)BF3.0Et2, CH2CI2 , -10°C to -5°C, 2h. Table 3: Blood schizontocidal activity of compounds 6a-g against P.yoelii in mice (Table Removed) (Formula Removed) We Claim: 1. Novel lipophilic ether derivatives of dihydroartemisinin having the following formula 6 (Formula Removed) wherein, R is a biphenyl or adamantly group selected form 2-Biphenylmethyl, 4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl represented by the chemical formula 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j and 6k given here as under: (Formula Removed) 2. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claim 1, wherein the said compounds exhibit the alpha isomeric form represented by the structural formula 7 as shown below: 3. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claim 1, wherein the said compounds exhibit the beta isomeric form represented by the structural formula 8 as shown below: (Formula Removed) 4. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claims 1 to 3, wherein the said compounds are in the form of an alpha isomer, a beta isomer or a combination thereof 5. A process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin as claimed in cliam 1, wherein the process comprises: a] reacting dihydroartemisinin of formula 2 (Formula Removed) with lipophilic alcohols of general formula 5 represented as R-OH, wherein R represents 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl under acidic conditions at a temperature ranging from -100C to270C in the presence of an acidic catalyst and organic solvent such as herein described; b] neutralization of the product obtained from step [a] with an organic solvent; c] washing the product obtained from step [b]; d] drying the washed product of step [c] by conventional methods; e] purifying the product obtained from step [d] to obtain the compound of formula 6. 6. A process as claimed in claim 5, wherein the acid catalyst used is selected from the groups consisting of diethoxyborontrifluoride, paratoluenesulfonic acid, hydrochloric acid, sulfuric acid and cation exchanger. 7. A process as claimed in claim 5, wherein the organuic solvent used is selcted from groups consisting of dichloroethane, benzene, chloroform and tetrahydrofuran. 8. A process as claimed in claim 5, wherein the purification of compounds is carried out by colunm chromatography and the products so obtained are mixtures of a and ß isomers, which can be further separated by column chromatography to give pure a- isomers of general formula 7 and ß- isomers of general formula 8 wherein R has the same meaning as above. 9. Novel lipophilic ether derivatives of dihydroartemisinin substantially as herein described with reference to the foregoing examples. 10. A process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin substantially as herein described with reference to the foregoing examples.

Full Text

This invention relates to novel lipophilic ether derivatives of dihydroartemisinin. The invention also relates to a process for the preparation of the said compounds. The compounds of the present invention are useful as antimalarials.
This invention generally relates to a process for the preparation of lipophilic ethers of dihydroartemisinin 2 of general formula 6 as a new series of antimalarials which are active by both i.m. and oral routes. More particularly the present invention relates to new ether derivatives of dihydroartemisinin of general formula 6 wherein R represent groups such as 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1 -Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl and the like. Some of these compounds are several times more potent than the current artemisinin-based antimalarials such as artemether 3 and arteether 4. Dihydroartemisinin is available from reduction of artemisinin 1, a natural product antimalarial from Artemisia annua. [For background literature on artemisinin and its derivatives see: (a) Klayman, D. L Science 1985, 228, 1049. (b) Bhattacharya, A. K.; Sharma, R. P. Heterocycles 1999, 51, 1651. (c) Borstnik, K.; Paik, I.; Shapiro, T. A.; Posner, G. H. Int. J. Parasitol. 2002, 32, 1661. (d) Ploypradith, P. Acta Trop. 2004, 89, 329. (e) O'Neill, P. M.; Posner, G. H. J. Med. Chem. 2004, 47, 2945.]
The main objective of this invention is to provide novel lipophilic ether derivatives of dihydroartemisinin which are more potent antimalarials than the clinically useful ether derivatives of the dihydroartemisinin such as artemether and arteether.
These compounds have been tested against multi-drug resistant Plasmodium yoelii in mice and have been found several times more active than artemether and arteether by oral route. Thus, the invention relates to pharmaceutical industry.
Accordingly, the present invention provides novel lipophilic ether derivatives of dihydroartemisinin having the following formula 6

(Formula Removed)

wherein, R is a biphenyl or adamantly group selected form 2-Biphenylmethyl, 4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl represented by the chemical formula 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j and 6k given here as under:

(Formula Removed)
The present invention also provides a process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin, wherein the process comprises:

(Formula Removed)
with lipophilic alcohols of general formula 5 represented as R-OH, wherein R represents 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl under acidic conditions at a temperature ranging from -10°C to 27°C in the presence of an acidic catalyst and organic solvent such as herein described;
b] neutralization of the product obtained from step [a] with an organic solvent;
c] washing the product obtained from step [b];
d] drying the washed product of step [c] by conventional methods;
e] purifying the product obtained from step [d] to obtain the compound of formula 6.
In an embodiment of the present invention the reaction of dihydroartemisinin of formula 2 with lipophilic alcohols of general formula 5 may be effected under acidic conditions using acidic catalysts such as BF3.OEt2, p-toluenesulphonic acid (PTSA), coned HCl, coned H2SO4, cation exchanger such as Amberlyst-15 and the like.
In another embodiment of the invention the organic solvent used may be chosen such as CH2CI2, C6H6,CHCl3,THF etc.
Purification of compounds of general formula 6 wherein R has the same meaning as above, may be carried out by column chromatography using combination of organic solvents as eluants. The products which are mixtures of a and (3 isomers can be further separated by column

chromatography to give pure a- isomers of general formula 7 and ß- isomers of general formula 8 wherein R has the same meaning as above.

(Formula Removed)
ihydroartemisinin of formula 2 is prepared by reduction of artemisinin 1 by known process. The compounds of the general formula 6, 7, and 8 are new and have not been prepared earlier. This invention is further illustrated by the following examples which should not, however, be construed to limit the scope of the present invention.
EXAMPLE 1 4-Biphenylmethyl ether of dihydroartemisinin [compound 6a,7a & 8a, formula 6, 7 and 8, R= 4-Biphenylmethyl]
To a solution of dihydroartemisinin (1.5g, 5.28 mmol) and biphenyl-4-yl-methanol (l.Og, 5.43 mmol) in 50ml dichloromethane was added BF3.0Et2 (4 drops) at -10°C to -5°C. The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave pure 8a as a solid (1.26g, 53.2%); m.p. 49-510C, a mixture of 7a & 8a (0.23g, 9.7%) and pure 7a as a solid (0.18g, 7.6%); m.p.79-80°C (combined yield 70.5%).
EXAMPLE 2 4-Biphenylethyl ether of dihydroartemisinin [compound 6b & 8b, formula 6, 7 and 8, R=4-biphenylethyl]
To a solution of dihydroartemisinin (l.Og, 3.52mmol) and 4-biphenylethanol (700mg, 3.53 mmol) in 50ml dichloromethane was added BF3.0Et2 (4 drops) at -100C to -50C.The mixture was stirred at the same temperature for 24h. The reaction mixture was then neutralized with
saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethyl acetate/hexane (3:97) as eluant gave pure 8b as a solid (1.34g, 82.2%); m.p.l 10-112°C.
EXAMPLE 3 2-(biphenyl-4-yloxy) ethyl ether of dihydroartemisinin [compound 6c,7c & 8c, formula 6, 7 and 8, R=2-(biphenyl-4-yloxy) ethyl]
To a solution of dihydroartemisinin (0.55g, 1.94mmol) and 2-(Biphenyl-4-yloxy)-ethanol (500mg, 2.33 mmol) in 40ml dichloromethane was added BF3.0Et2 (4 drops) at -100C to -50C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:24) as eluant gave pure 8c as a white solid (360mg, 38.7%); m.p. 111-112° C, a mixture of 7c & 8c (lOOmg, 10.7%) and pure 7c as a white solid (160mg, 17.2%); m.p.l08-109°C (combined yield 66.6%).
Compound 7c & 8c was also prepared using different reaction conditions. Results are summarized in table 1.
Table 1.

(Table Removed)
EXAMPLE 4 l-Adamantanemethyl ether of dihydroartemisinin (compound 6d, formula 6, R= 1-Adamantanemethyl)
To a solution of dihydroartemisinin (900mg, 3.17mmol) and Adamantan-1-yl-methanol (585mg, 3.52 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for Ih. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave an inseparable 1:3 mixture of 6d as a white crystalline solid (1.24g, 91.1%); m.p. 146-147°C.
EXAMPLE 5 2-Adamaiitanyl ether of dihydroartemisinin (compound 6e, formula 6, R=2-Adamantanyl)
To a solution of dihydroartemisinin (800mg, 2.81mmol) and 2-adamantanol (535mg, 3.51 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C. The mixture was stirred at the same temperature for Ih. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (20ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave an inseparable 1:3 mixture of 6e as a white solid (1.43g, 96.5%); m.p. 136-138°C.
EXAMPLE 6 2-(biphenyl-2-yloxy) ethyl ether of dihydroartemisinin [compound 6f,7f & 8f, formula 6, 7 and 8, R=2-(biphenyl-2-yloxy) ethyl]
To a solution of dihydroartemisinin (800mg, 2.81mmol) and 2-(Biphenyl-4-yloxy)-ethanol (750mg, 3.5 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -10°C to -5'C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd.
Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (3:97) as eluant gave pure 8f as a solid (740mg, 54.8%); m.p. 90-92°C, a mixture of 7f & 8f (230 mg, 17.0%) and pure 7f as a solid (300mg, 22.2%); m.p.l03-105°C (combined yield 94.0%).
EXAMPLE 7 2-Biphenylmethyl ether of dihydroartemisinin (compound 6g & 8g, formula 6, 7 and 8, R=2- Biphenylmethyl)
To a solution of dihydroartemisinin (800mg, 2.81mmol) and Biphenyl-2-yl-methanol (650mg, 3.53 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C. The mixture was stirred at the same temperature for 1.25h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave the mixture of a- and (3- isomers as a solid (1.13g, 96.5%) which on crystallization in CH2Cl2 /hexane gave pure 8g as a white crystalline solid (250mg, 21.3%); m.p. 130-132°C.
EXAMPLE 8 2-(9H-fluoren-9-yl) - ethyl ether of dihydroartemisinin [compound 6h, formula 6, R= 2-(9H-nuoren-9-yl) - ethyl]
To a solution of dihydroartemisinin (0.50g, 1.76mmol) and 2-(9H-fluoren-9-yl)- ethanol (0.55g , 2.62 mmol ) in 40ml dichloromethane was addedBF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for 3h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x20ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (3:97) as eluant gave an 1:4 mixture of 6h as a white solid (0.83g, 99.0%);m.p. 131-1330C.
EXAMPLE 9 (9H-fluoren-9-yl)-methyl ether of dihydroartemisinin [compound 6i,7i & 8i, formula 6, 7 and 8, R= (9H-fluoren-9-yl) - methyl]
To a solution of dihydroartemisinin (0.50g, 1.76mmol) and (9H-fluoren-9-yl)-methanol(0.51g, 2.60 mmol ) in 30ml dichloromethane was added BF3.OEt2 (4 drops) at -10°C to -5'C.The mixture was stirred at the same temperature for 2h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25 ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethyl acetate / hexane (1:49) as eluant gave pure 7i as a white solid (O.lOg, 12.3%); m.p. 100-102°C, a mixture of 7i & 8i (0.09g, 11.0%) and pure 81 as a white solid (430 g, 52.8%); m.p.l36-138°C (combined yield 76.2%).
EXAMPLE 10 2-adamamantan-l-yl-ethyl ether of dihydroartemisinin [compound 6j,7j & 8j, formula 6, 7 and 8, R= 2-adamantan-l-yl -ethyl]
To a solution of dihydroartemisinin (l.0g, 3.52 mmol) and 2- adamantan-1-yl-ethanol (0.95g, 5.27 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -5°C.The mixture was stirred at the same temperature for 9h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:49) as eluant gave 1:3 mixture of 7j & 8j (1.24g ,78.9%)) which on flash chromatography over flash silica gel using ethyl acetate/hexane (0.75:99.25) as eluant gave pure 8j as a white solid (0.29g , 18.4 %); m.p. 65-67 °C, a mixture of 7j & 8j (0.88g , 56.0%) and pure 7j as an oil (0.07g , 4.4%).
EXAMPLE 11 2-adamantan-2-yl-ethyl ether of dihydroartemisinin [compound 6k, 7k & 8k, formula 6,7 and 8, R= 2-adamantan-2-yl -ethyl]
To a solution of dihydroartemisinin (l.Og, 3.52 mmol) and 2-adamantan-2-yl-ethanol (0.950 g, 5.27 mmol) in 40ml dichloromethane was added BF3.OEt2 (4 drops) at -100C to -50C.The
mixture was stirred at the same temperature for 9h. The reaction mixture was then neutralized with saturated sodium bicarbonate solution (25ml) and extracted with dichloromethane (3x25ml). The organic layer was washed with water (10ml), dried over anhyd. Na2S04 and concentrated under reduced pressure. The crude product on column chromatography over silica gel using ethylacetate/hexane (1:99) as eluant gave 1:3 mixture of 7k & 8k (1.27g, 81.2%) which on flash chromatography over flash silica gel using ethylacetate/hexane (0.2:99.8) as eluant gave pure 8k as a solid (0.58 g, 36.9%); m.p. 50-52 °C, a mixture of 7k & 8k (0.586g, 37.3%) and pure 7k as a white solid (0.llg, 7.0%); m.p. 75-77°C (combined yield 81.2%). Following the above procedure the following lipophilic ether derivatives of dihydroartemisinin 6a,7a, 8a,6b, 8b, 6c,7c, 8c, 6d, 6e, 6f, 7f, 8f, 6g,8g, 6h, 6i,7i, 8i,6j, 7j, 8j,6k, 7k and 8k were prepared (scheme 1, table 2).
Table 2
(Table Removed)
[compound 6b & 8b, formula 6, 7 and 8, R=4-
biphenylethyl]
~3^ 2-(biphenyl-4-yloxy) ethyl ether of 7c:108-109"C 66.6
dihydroartemisinin [compound 6c, 7c i& 8c, 8c:lll-112V
formula 6, 7 and 8, R=2-(biphenyl-4-yloxy)
ethyl]
Z 1-Adamantanemethyl ether of 6d:146-147V 9U
dihydroartemisinin (compound 6d, formula 6,
R= 1-Adamantanemethyl)
5. 2-Adamaiitanyl ether of dihydroartemisinin 6e:136-138V 96.5
(compound 6e, formula 6, R=2-Adamantanyl)
6] 2-(biphenyl-2-yloxy) ethyl ether of 7f: 94.0
dihydroartemisinin [compound 6f,7f & 8f, 103-1050C
formula 6, 7 and 8, R=2-(biphenyl-2-yloxy) 8f:
ethyl] 90-92V
7. 2-Biphenylmethyl ether of dihydroartemisinin 8g: 96.5
(compound 6g & 8g, formula 6, 7 and 8, R=2- 130-132V
Biphenyl methyl)
8. 2-(9H-fluoren-9-yl) ^ ethyl ether of 6h:131-133V 99.0
dihydroartemisinin [compound 6h, formula 6,
R= 2-(9H-fluoren-9-yl) - ethyl]
9. (9H-fluoren-9-yl)-methyl ether of 7i; 762
dihydroartemisinin [compound 6i,7i & 8i, 100-102°C
formula 6, 7 and 8, R= (9H-fluoren-9-yl) - 8i:
methyl] 136-138°C
10. 2-adamantan-l-yl-ethyl ether of 8j: 78.9
dihydroartemisinin [compound 6j,7j & 8j, 65-67°C
formula 6, 7 and 8, R= 2-adamantan-l-yl -ethyl]
11 2-adamantan-2-yl-ethyl ether of 7k: 81.2
dihydroartemisinin [compound 6k,7k & 8k, 75-77 °C
formula 6,7 and 8, R= 2-adamantan-2-yl -ethyl] 8k:
Antimalarial activity
The blood schizontocidal activity of the test compounds was evaluated in rodent model using multi-drug resistant strain of Plasmodium yoelii nigeriensis in Swiss mice.
General procedure
Random bred Swiss mice of either sex (20 ± 2 g) were inoculated intraperitoneally with 1x105 P. yoelii (MDR) parasites on day zero. The treatments with test compounds were administered to group of 6 mice each at different dose levels ranging between 12-48 mg/kg/day. The compounds were administered as solutions in oil via oral route for 4 consecutive days (day 0-3). P-Arteether and a-Arteether was used as positive control.
Blood smears from experimental mice were observed on day 4 and 7, day 10 and thereafter at regular interval till day 28 or death of the animal. The parasitaemia level on day 4 was compared with the vehicle control group and the percent suppression of parasitaemia in treated groups was calculated. The compounds which showed more than 90%suppression were identified for further screening.
For determing the curative dose of a compound the treated mice were observed till day 28.The dose at which no parasitaemia develops during the observation period has been recorded as the curative dose. The results are shown in table 3.
(Table Removed)

Scheme 1 Reagents and conditions: (a)BF3.0Et2, CH2CI2 , -10°C to -5°C, 2h.
Table 3: Blood schizontocidal activity of compounds 6a-g against P.yoelii in mice

(Table Removed)
(Formula Removed)

We Claim:
1. Novel lipophilic ether derivatives of dihydroartemisinin having the following formula 6
(Formula Removed)
wherein, R is a biphenyl or adamantly group selected form 2-Biphenylmethyl, 4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl represented by the chemical formula 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j and 6k given here as under:

(Formula Removed)

2. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claim 1, wherein the said compounds exhibit the alpha isomeric form represented by the structural formula 7 as shown below:
3. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claim 1, wherein the said compounds exhibit the beta isomeric form represented by the structural formula 8 as shown below:
(Formula Removed)

4. Novel lipophilic ether derivatives of dihydroartemisinin as claimed in claims 1 to 3, wherein the said compounds are in the form of an alpha isomer, a beta isomer or a combination thereof
5. A process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin as
claimed in cliam 1, wherein the process comprises: a] reacting dihydroartemisinin of formula 2
(Formula Removed)
with lipophilic alcohols of general formula 5 represented as R-OH, wherein R represents 2-Biphenylmethyl,4-Biphenylmethyl, 4-Biphenylethyl, 2-(biphenyl-2-yloxy) ethyl, 2-(biphenyl-4-yloxy) ethyl, 1-Adamantanemethyl, 2-Adamantanyl, 2-adamantan-l-yl-ethyl, 2-adamantan-2-yl-ethyl, 2-(9H-fluoren-9-yl) - ethyl, (9H-fluoren-9-yl)-methyl under acidic conditions at a temperature ranging from -100C to270C in the presence of an acidic catalyst and organic solvent such as herein described;
b] neutralization of the product obtained from step [a] with an organic solvent;
c] washing the product obtained from step [b];
d] drying the washed product of step [c] by conventional methods;
e] purifying the product obtained from step [d] to obtain the compound of formula 6.

6. A process as claimed in claim 5, wherein the acid catalyst used is selected from the groups consisting of diethoxyborontrifluoride, paratoluenesulfonic acid, hydrochloric acid, sulfuric acid and cation exchanger.
7. A process as claimed in claim 5, wherein the organuic solvent used is selcted from groups consisting of dichloroethane, benzene, chloroform and tetrahydrofuran.
8. A process as claimed in claim 5, wherein the purification of compounds is carried out by colunm chromatography and the products so obtained are mixtures of a and ß isomers, which can be further separated by column chromatography to give pure a- isomers of general formula 7 and ß- isomers of general formula 8 wherein R has the same meaning as above.
9. Novel lipophilic ether derivatives of dihydroartemisinin substantially as herein described with reference to the foregoing examples.
10. A process for the preparation of novel lipophilic ether derivatives of dihydroartemisinin substantially as herein described with reference to the foregoing examples.

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Patent Number

271422

Indian Patent Application Number

209/DEL/2004

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

19-Feb-2016

Date of Filing

13-Feb-2004

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	CHANDAN SINGH	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PLACE, LUCKNOW-226 001, (U.P.), INDIA.
2	SANDEEP CHAUDHARY	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PLACE, LUCKNOW-226 001, (U.P.), INDIA.
3	SUNIL KUMAR PURI	CENTRAL DRUG RESEARCH INSTITUTE, CHATTAR MANZIL PLACE, LUCKNOW-226 001, (U.P.), INDIA.

PCT International Classification Number

A61K 31/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA