Title of Invention

2 - AMINO-3-(N-SUBSTITUTED CARBOXAMIDO)-4,5-POLYMETHYLENE THIOPHENE DERIVATIVES AND A PROCESS FOR OBTAINING THE SAME

Abstract

The invention provides a process for obtaining 2-amino-3-(N-substituted carboxamido )-4,5-polymethylene thiophene. More particularly, the Invention provides a method of obtaining 2-amino-3-(N-substituted carboxamido)-4,5- .polymethylene thiophene comprising of condensation of ethyl cyanoacetate with substituted anilines, isolation of the intermediate by the reaction between ketones and substituted cyano anilides, and reaction of the intermediate with sulphur under specific condition to obtain 2-amino-3-(N-substituted carboxamido )-4,5-polymethylene thiophene. Further the invention advantageously utilizes the said process for obtaining 2-substituted derivatives of 2-amino-3-(N -substituted carboxamido )-4,5-polymethylene thiophene. The invention also provides a new molecular scaffold employing the product of the process claimed under the application. The 2-amino-3-(N-substituted carboxamido )-4,5-polymethylene thiophene and its 2-substituted derivatives exhibit enhanced anti inflammatory and analgesic activities.

Full Text

2- AMINO-3-(N-SUBSTITUTED CARBOXAMIDO)-4,5-POLYMETHYLENE THIOPHENE DERIVATIVES AND A PROCESS FOR OBTAINING THE SAME Field of invention: [001] The invention relates to the field of pharmaceutical chemistry and more particularly to a process of obtaining 2- Amino-3-(N- Substituted Carboxamido)-4,5-Polymethylene Thiophene Derivatives. State of Art: [002] Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. The term "non-steroidal" is used to distinguish these drugs from steroids, which (among a broad range of other effects) have a similar eicosanoid-depressing, anti-inflammatory action. As analgesics, NSAIDs are unusual in that they are non-narcotic. NSAIDs are sometimes also referred to as non-steroidal anti-inflammatory agents/analgesics (NSAIAs) or non-steroidal anti¬inflammatory medicines (NSAIMs). The most prominent members of this group of drugs are aspirin, ibuprofen, and naproxen partly because they are available over-the-counter in many areas. Paracetamol (acetaminophen) has negligible anti¬inflammatory activity, and is strictly speaking not an NSAID. [003] NSAIDs can be broadly classified based on their chemical structure. NSAIDs within a group will tend to have similar characteristics and tolerability. There is little difference in clinical efficacy between the NSAIDs when used at equivalent doses. # Rather, differences between compounds tended to be with regards to dosing regimens (related to the compound's elimination half-life), route of administration, and tolerability profile. Some more common examples are given below. [004] Tylenol also called Paracetamol (acetaminophen) is grouped together with the NSAIDs, however, it does not have any significant anti-inflamrnatory properties and is not a true NSAID. Though the mechanism of action is unclear, it is suspected that the lack of anti-inflammatory action may be due to inhibition of cyclooxygenase predominantly in the central nervous system. There is also some speculation that Tylenol acts through the inhibition of the recently discovered COX-3 isoform. The other chemical classes known to act as NSAIDS are • Salicylates comprising of drugs such as Aspirin, Amoxiprin, Benorilate, Choline magnesium, salicylate, Diflunisal, Faislamine, Methyl salicylate and Magnesium Salicylate. • Arylalkanoic acids such as Salicyl salicylate (salsalate), Diclofenac, Aceclofenac, Acemetacin, Bromfenac, Etodolac, Indometacin, Nabumetone, Sulindac, Tolmettn • 2-Arylpropionic acids (profens) such as Ibuprofen, Carprofen, Fenbufen, Fenoprofen, Flurbiprofen, Ketoprofen, Ketorolac, Loxoprofen, Naproxen, Oxaprozin, Tiaprofenic acid, Suprofen • Af-Arylanthranilic acids (fenamic acids) such as Mefenamic acid, Meclofenamic acid • Pyrazolidine derivatives such as Phenylbutazone, Azapropazone, Metamizole, Oxyphenbutazone, Sulfinprazone. • Oxicams such as Piroxicam, Lornoxicam, Meloxicam, Tenoxicam. • COX-2 Inhibitors such as Celecoxib (FDA alert [1]), Etoricoxib, Lumiracoxib TGA cancelled registration, Parecoxib FDA withdrawn, Rofecoxib (withdrawn from market [2]), Valdecoxib (withdrawn from market [3]) l. SulphonaniHdes such as Nimesulide [005] However, many of the mentioned NSAIDs have effects others than what they are intended to have such as adverse effects, combinatorial risk, cardiovascular risk and gastrointestinal risks. [006] Adverse effects: The widespread use of NSAIDs has meant that the adverse effects of these relatively safe drugs have become increasingly prevalent. The two main adverse drug reactions (ADRs) associated with NSAIDs relate to gastrointestinal (GI) effects and renal effects of the agents. [007] These effects are dose-dependent, and in many cases severe enough to pose the risk of ulcer perforation, upper gastrointestinal bleeding, and death, limiting the use of NSAID therapy. According to a report known in the prior art an estimated 10-20% of NSAID patients experience dyspepsia. There are reports, which project that NSAID-associated upper gastrointestinal adverse events results in 103,000 hospitalizations and 16,500 deaths per year in the United States alone and represent 43% of drug-related emergency visits [008] Gastrointestinal ADRs: The main ADRs (adverse drug reactions) associated with use of NSAIDs relate to direct and indirect irritation of the gastrointestinal tract (GIT). NSAIDs cause a dual insult on the GIT - the acidic molecules directly irritate the gastric mucosa; and inhibition of COX-1 reduces the levels of protective prostaglandins. Common gastrointestinal ADRs include Nausea/Vomiting, Dyspepsia, Gastric ulceration/bleeding and Diarrhea. Further, risks of ulceration increases with duration of therapy, and with higher doses. In attempting to minimise GI ADRs, it is prudent to use the lowest effective dose for the shortest period of time, a practice that is not often followed. [009] There are also some differences in the propensity of individual agents to cause gastrointestinal ADRs. Indomethacin, ketoprofen and piroxicam appear to have the highest prevalence of gastric ADRs, while ibuprofen (lower doses) and diclofenac appear to have lower rates. Commonly, gastrointestinal adverse effects can be reduced through suppressing acid production, by concomitant use of a proton pump inhibitor, e.g. omeprazole; or the prostaglandin analogue misoprostol. Misoprostol is itself associated with a high incidence of gastrointestinal ADRs (diarrhoea). While these techniques may be effective, they prove to be expensive for maintenance therapy. [0010] Renal ADRs: NSAIDs are also associated with a relatively high incidence of renal ADRs. The mechanism of these renal ADRs is due to changes in renal haemodynamics (blood flow), ordinarily mediated by prostaglandins, which are affected by NSAIDs. Prostaglandins normally cause vasodilation of the afferent arterioles of the glomeruli. This helps maintain normal glomerular perfusion and glomerular filtration rate (GFR), an indicator of renal function. By blocking this prostaglandin-mediated effect, NSAIDs ultimately may cause renal impairment. Horses are particularly prone to these adverse affects compared to other domestic animal species. [0011] Common ADRs associated with altered renal function include effects such as Salt and fluid retention and Hypertension. In rarer instances NSAIDs may also cause more severe renal conditions such as Interstitial nephritis, Nephrotic syndrome, Acute renal failure, Acute tubular necrosis. [0012] Apart from ADRs described in detail above, the NSAIDs available are not effective in providing the necessary anti-inflammatory and analgesic effects. The efficacy of a drug compound is often established by parameters such as Absorption, Distribution, Metabolism and Elimination. These parameters are referred to as ADME and are equally important when compared to Toxicity effects described earlier herein through ADRs. There is a need for a drug compound, which increases efficacy by improved ADME parameters and reduced ADRs. The invention herein provides for a new class of compounds, which have an improved efficacy over known NSAIDs in providing enhanced Anti-inflammatory and Analgesic effects. Object of the Invention: [0013] It is an object of the invention to provide a new molecular scaffold for analgesic and anti-inflammatory activities. [0014] More particularly, it is an object of the invention to provide a process for obtaining 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene and its 2-substituted derivatives. Brief Description of the Drawings: [0015] Figure 1 represents the Condensation Reaction Step wherein Ethyl cyano acetate is condensed with substituted anilines to obtain anilides. [0016] Figure 2 represents first reaction step of the obtained anilides with different ketones under certain specific conditions to obtain the reaction intermediates. [0017] Figure 3 represents the second reaction step to obtain the 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes. [0018] Figure 4 represents structure of 2-ammo-3-(N-substituted carboxamido)-4,5-polymethyIene thiophene according to an embodiment of the invention. [0019] Figure 5 represents structure of methyl derivative of 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene according to an example of the invention [0020] Figure 6 represents the Markuish structure of 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes. Summary of the Invention: [0021] The invention provides a new molecular scaffold for enhanced analgesic and anti-inflammatory activities. More particularly the invention provides a process for obtaining 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene and its 2-substituted derivatives. The said process of obtaining the said 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene comprises of: a) Condensation of ethyl cyanoacetate with substituted anilines, b) Isolation of the intermediate by the reaction between ketones and substituted cyano anilides under specific condition and c) Reaction of the intermediate with sulphur under specific condition to obtain 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene. [0022] The analgesic and anti-inflammatory activities of the new compounds have been evaluated by both in-vitro and in-vivo studies. The in-vitro studies conducted comprises of determining antioxidant, superoxide anion scavenging and lipid peroxidation inhibiting activities. The in-vivo studies involves acetic acid induced writhing method and carrageenan induced rat hind paw oedema method. [0023] The process of obtaining the said 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene and its 2-substituted derivatives and the evaluation of analgesic and anti-inflammatory activities are described in detail below. Detailed Description of the Invention: [0024] The invention provides a new molecular scaffold for enhanced analgesic and anti-inflammatory activities. More particularly the invention provides a process for obtaining 2-amino-3-{N-substituted carboxamido)-4,5-polymethylene thiophene and its 2-substituted derivatives. [0025] The said process of obtaining the said 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene comprises of: a) Condensation of ethyl cyanoacetate with substituted anilines, b) Isolation of the intermediate by the reaction between ketones and substituted cyano anilides under specific condition and c) Reaction of the intermediate with sulphur under specific condition to obtain 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene. Each of the steps mentioned above shall be described herein in detail. [0026] Condensation of ethyl cyanoacetate with substituted anilines: In an embodiment of the invention, substituted aniline in the concentration range between 0.5 Molar(M) and 2.0M is mixed with ethyl cyanoacetate in the concentration range of 0.2M to l.OM and heated at temperatures in the range of 150°C to 170°C for a time duration of 7 to 9 hours. In a preferred embodiment of the invention, l.OM concentration of substituted aniline is mixed with 0.665M concentration of ethyl cyanoacetate and heated at a temperature of 160°C for 8 hours. The reaction mixture is left at room temperature, overnight. The solid obtained is then removed, washed with ethanol, dried and then re-crystallized using a suitable solvent to obtain a first intermediate a-(N-aryl carboxamido) a -alkylidene acetonitrile. The above described reaction is summarized in Figure 1. [0027] Isolation of the intermediate by the reaction between ketones and substituted cyano anilides under specific condition: A mixture of ketone, in the concentration range of 0.02M to 0.06M (0.04M); substituted cyano-anilide, in the concentration range of 0.02M to 0.06M (0.04M); ammonium acetate, in the range 1 to 2g and glacial acetic acid in the concentration range of 2 to 4ml, is dissolved in 80 to 100ml of benzene. The above mixture is refluxed for a time duration of 8 to 10 hours in Dean Stark apparatus provided with an arrangement for continuous separation of water. The reaction mixture is cooled, diluted with benzene and washed with water, sodium carbonate (10%W/V in water) and dried over anhydrous sodium sulphate for 10-20 minutes. Then the solvent is removed under vacuum to obtain second intermediate 2-amino thiophene 3-carboxanilide. The intermediate obtained is used directly for the next step. [0028] c) 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes: About 30-50ml of alcohol was added to the 2-amino thiophene 3-carboxanilide obtained. To this reaction mixture Sulphur in the concentration of about 0.04M is added with stirring and the temperature maintained at about 40-45°C during addition. Further about 3-5ml Diethylamine is added drop wise with stirring. The process of stirring is continued for about 1 hour at a temperature of about 40-45°C and chilled overnight. The solid obtained is then filtered, washed with ethanol and re-crystallised using a suitable solvent to obtain 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes. [0029] The following description provides method for obtaining derivatives of 2-ammo-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes. The derivatives obtained are explained as examples of the invention; [0030] Example 1: 2-benzoylamino-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes: The parent compound (0.005 mol) was dissolved in pyridine (15-25 ml). To this benzoyl chloride (0.015M) was added drop wise and then stirred for 1 hour on a magnetic stirrer. The reaction mixture was then poured in to ice cold water with stirring. The product obtained was filtered and washed with excess of ice cold water to remove the pyridine. The product obtained was purified by washing with hot ethanol and then crystallized using a suitable solvent. [0031] Example 2: Preparation of aromatic acid chlorides;The aromatic acid chlorides such as p- chloro benzoyl chloride , p-methoxy benzoyl chloride, m-methoxy benzoyl chloride, m-bromo benzoyl chloride, p-nitro benzoyl chloride, o-chloro benzoyl chloride were prepared by refluxing 0.1M of each corresponding acid in 0.3M of thionyl chloride for 1- 2 hours. The excess of thionyl chloride was removed by distillation under reduced pressure. The acid chloride obtained was used immediately. [0032] Example 3: 2-(p-methoxybenzamido)-3-(N-substituted carboxamido)-4,5-polymethylene thiophenes: 0.005 mol of the parent compound, 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene is dissolved in pyridine (15-25 ml). To this p-methoxy benzoyl chloride (0.015M) is added drop wise and then stirred for about an hour on a magnetic stirrer. The reaction mixture is then poured into ice cold water with continued stirring. The product obtained is filtered and washed with excess of ice cold water to remove the pyridine. The product obtained is purified by washing with hot ethanol and then crystallized using a suitable solvent. [0033] The process described above explains in detail the method of obtaining 2-amino-3-(N-substituted caboxamido)-4,5- polymethylene thiophene and its 2-substituted derivatives. The parent compound thus obtained along with derivatives are tested for its analgesic and anti inflammatory activities. [0034] The analgesic and anti-inflammatory activities of the new compounds have been evaluated by both in-vitro and in-vivo studies. The in-vitro studies conducted comprises of determining antioxidant, superoxide anion scavenging and lipid peroxidation inhibiting activities. The in-vivo studies involves acetic acid induced writhing method and carrageenan induced rat hind paw oedema method. Each of the above mentioned studies is explained in detail below. [0035] ANALGESIC ACITIVITY: In an example of the invention Acetic acid induced writhing method is adopted to estimate the analgesic activity. In this method, about 50 albino mice weighing between 30g and 35g are selected. One percent weight/volume(w/v) Acetic acid solution is prepared. Aspirin dispersed in water as an aqueous suspension with 0.2%solution of tween 80 as a suspending agent is chosen as reference drug.Compounds synthesized SMALRT-IO, SMALRT-11, SMALRT- 15, SMALRT-18, SMALRT-19, SMALRT-23 were prepared as an aqueous suspension using tween 80 as a suspending agent and administered orally. In an example of the invention the dose administered was lOOmg/Kg body weight. [0036] Working Procedure: Albino mice of either sex are divided into different groups and numbered individually. In an example of the invention, 48 albino mice are divided into eight groups each comprising of six animals. Animals belonging to each group are fasted for 24 hours before administration of the drug with water. Two groups of animals receive the test sample, where as one group receive reference drug aspirin at a dose of 0.1 ml./lO gm body weight. The control group is administered with the 0.1ml/10 gm body weight of 2% w/v Tween 80. Two other groups receive O.lml/lOg body weight of test compounds SMALRT-10, SMALRT-11, SMALRT-15 SMALRT-18, SMALRT-19, SMALRT-23. After 15 minutes of this administration, writhing is induced by intraperitoneal injection of 1% acetic acid in the volume of 0.1 ml./lO gm body weight and the writhing episodes recorded for 10 minutes.. The percentage protection against the writhing episodes in the standard and drug treated animals are recorded and calculated by using the formula; % Protection (1—WVWc)x 100 Where, Wt: Mean of writhing episodes in test Wc: Mean of writhing episodes in control. [0037] ANTIINFLAMMATORY ACTIVITY: In an example of the invention, Carrageenan induced rat hind paw oedema method is adopted to estimate anti¬inflammatory activities. In this method about 50 Swiss albino rats weighing 150-200g are selected 1%W/V solution of Carrageenan in distilled water is utilized as an inflammation inducer and 0.1ml of the said solution is injected in plantar region to induce foot oedema. Aqueous suspension of Ibuprofen prepared with 0.2%solution of tween 80 as a suspending agent is utilized as reference drug. In an example of the invention a dose of lOOmg/Kg is administered. Suspensions of compounds SMALRT-IO, SMALRT-I1, SMALRT- 15, SMALRT-18, SMALRT-19, SMALRT-23 are prepared and administered similar to the standard drug. [0038] Working Procedure: 1. Forty eight albino rats of either sex were divided into eight different groups of six animals and they were numbered individually. 2. Animals were fasted for 24 hours before administration of the drug with water administration. 3. The animals were marked on their hind paw just beyond tibio-tarsal junction to ensure constant dipping in the mercury column up to a fixed mark. 4. The initial paw volume (both right and left) of each rat was noted by mercury displacement method using Plethysmograph, 5. Animals in the group III to VIII received the test samples, whereas group II received Ibuprofen at a dose of 10.6mg/200g body weight, which served as standard. 6. Group I which served as control was administered with 0.1ml of 1%W/V carrageenan solution. 7. After drug treatment, 0.1ml of 1%W/V carrageenan solution was injected into plantar region of the left paw of the standard and test groups. 8. The paw volume of both the legs of control and standard groups was measured with the help of Plethysmograph for 30, 60,120,240 and 360 minutes after carrageenan administration. 9. The percentage of inhibition of inflammation in the drug treated animals were recorded and calculated using the formula % Inhibition= (1—Wt/Wc)x 100 Where, Wt: Mean oedema volume of control Wc: Mean oedema volume of drug Statement of Invention: [0038] The invention provides a process for obtaining 2-amino-3-(N-substituted carboxamido}-4,5-polymethylene thiophene and its 2 substituted derivatives. More particularly, the Invention provides a method of achieving 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene that comprises steps such as condensation of ethyl cyanoacetate with substituted anilines, isolation of the intermediate by the reaction between ketones and substituted cyano anilides, and reaction of the intermediate with sulphur under specific condition to obtain 2-amino-3-(N-substituted carboxamido)-4,5-polymethylene thiophene. The invention also provides a new molecular scaffold employing the product of the process claimed under the application. I Claim, 1. A process for obtaining 2-amino-3-(N-substituted carboxamido)-4,5- polymethylene thiophene and its 2 substituted derivatives, comprising the steps of: (i) condensing ethyl cyanoacetate with substituted anilines to obtain a first intermediate; (ii) reacting said first intermediate with ketones and substituted cyano anilides to obtain a second intermediate, and (iii) reacting said second intermediate with sulphur under specific condition to obtain 2-amino-3- (N-substituted carboxarnido)-4,5-polymethylene thiophene. 2. A process of Claim 1, wherein step (i) comprises: (a) mixing substituted aniline in the concentration range of about 0.5 Molar (M) to 2.0 M and ethyl cyanoacetate in the concentration range of 0.2 M to 1.0 M, and (b) heating said mixture to temperatures in the range of about 150°C to 170°C for a duration of about 7 to 9 hours to obtain said first intermediate. 3. A process of claim 2, wherein said first intermediate comprises a-(Naryl-carboxamido) a -alkylidene acetonitrile. 4. A process of Claim 1, wherein step(ii) comprises: (a) dissolving a synergistic mixture in 80ml to 100ml of benzene, said synergistic mixture comprising ketone in the concentration range of about 0.02 M to about 0.06 M and substituted cyano-anilide in the concentration range of about 0.02M to about 0.06M, ammonium acetate in the range 1 to 2g and glacial acetic acid in the concentration range of 2 to 4ml; (b) refluxing said dissolved mixture for 8Hrs to lOHrs, and (c) reacting a-(N-aryl carboxamido) a -alkylidene acetonitrile with refluxed mixture to obtain the second intermediate; 5. A process of claim 4 further comprising the drying the second intermediate over anhydrous sodium sulphate for about 10-20 minutes. 6. A process of claim 4 wherein the second intermediate comprises 2-aitiino thiophene 3-carboxanilide. 7. A process of claim 1 wherein step (iii) comprises the steps of: (a) mixing the second intermediate with 30ml to 50ml of alcohol, (b) adding 0.04 M concentration of sulphur in the temperature range of 40 to 45°C followed by stirring. (c) adding 3ml to 5ml diethylamine drop wise for about an 1 hour at a temperature range of 40 to 45°C, and (d) cooling until crystallization. 8. A new molecular scaffold comprising the structural formula:

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