This article was downloaded by: [Fondren Library, Rice University ] On: 24 September 2012, At: 00:57 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lsyc20 Synthetic and Thermogravimetric Studies of 5-Amino-2- ethoxycarbonylaminothiazoles Sibdas Ray a & Prabhat Kumar Ray b a Department of Chemistry, University College of Science, University of Calcutta, Kolkata, India b Department of Chemistry, P. K. College, Contai, Purba Medinipur, India Accepted author version posted online: 19 Dec 2011.Version of record first published: 14 May 2012. To cite this article: Sibdas Ray & Prabhat Kumar Ray (2012): Synthetic and Thermogravimetric Studies of 5-Amino-2-ethoxycarbonylaminothiazoles, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 42:16, 2355-2366 To link to this article: http://dx.doi.org/10.1080/00397911.2011.556411 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
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This article was downloaded by: [Fondren Library, Rice University ]On: 24 September 2012, At: 00:57Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: AnInternational Journal for RapidCommunication of Synthetic OrganicChemistryPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/lsyc20
Synthetic and ThermogravimetricStudies of 5-Amino-2-ethoxycarbonylaminothiazolesSibdas Ray a & Prabhat Kumar Ray ba Department of Chemistry, University College of Science, Universityof Calcutta, Kolkata, Indiab Department of Chemistry, P. K. College, Contai, Purba Medinipur,India
Accepted author version posted online: 19 Dec 2011.Version ofrecord first published: 14 May 2012.
To cite this article: Sibdas Ray & Prabhat Kumar Ray (2012): Synthetic and Thermogravimetric Studiesof 5-Amino-2-ethoxycarbonylaminothiazoles, Synthetic Communications: An International Journal forRapid Communication of Synthetic Organic Chemistry, 42:16, 2355-2366
To link to this article: http://dx.doi.org/10.1080/00397911.2011.556411
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.
SYNTHETIC AND THERMOGRAVIMETRIC STUDIES OF5-AMINO-2-ETHOXYCARBONYLAMINOTHIAZOLES
Sibdas Ray1 and Prabhat Kumar Ray21Department of Chemistry, University College of Science, University ofCalcutta, Kolkata, India2Department of Chemistry, P. K. College, Contai, Purba Medinipur, India
5-Amino-1-(50-phospho-b-D-ribofuranosyl)imidazole is the first biochemicalpurine precursor of imidazole origin. As cogeners of 5-aminoimidazoles, there are
Received December 7, 2010.
Address correspondence to Sibdas Ray, Department of Chemistry, University College of Science,
reports of 5-amino- and 5-azathiazole compounds as adenosine receptor antago-nists[1] and as tyrosine kinase inhibitors,[2] to show in vitro antitumor activity,[3]
and as drugs for the treatment of diabetes mellitus and impared glucose-tolerance.[4]
Thiazole compounds with amino group(s) at the C-2=C-5 position(s) are conspicu-ous for ring-transformation reactions.[5–7] In an early successful base-catalyzedring-transformation, Cook and his coworkers[5] converted 5-amino-4-phenyl-2-mer-captothiazole to 4-phenyl-5-mercaptoimidazole-2(1H, 3H)-thione. Ethanolic sodiumethoxide–induced transformation of 5-amino-3-methyl-4-ethoxycarbonylthiazoliumtosylate to ethyl 1-methyl-4-mercaptoimidazole-5-carboxylate has been reported tooccur in good yields.[6] A general synthesis of 5-amino-2-thioimidazole compounds by base-catalyzed rearrangement of 5-amino-2-substitute-daminothiazole compounds has also been developed.[7] These transformationscorrespond to the addition of nucleophile–ring opening–ring closure (ANRORC)sequence.
Thiazole ring with amino substituent(s) at C-2=C-4 is prone to showANRORC activity under basic reaction conditions. Reaction of 2-amino-2-cyanoa-cetamide with x-diethylaminoalkyl isothiocyanate, under reflux in ethyl acetate, gavethe desired product 5-amino-2-mercapto-1-(x-diethylaminoalkyl)imidazole-4-carboxamide.[8] The ring closure of the open-chain intermediate thiourea com-pound is driven in this direction because of the basic nature of the reactionmedium offered by the tertiary amino center present in the x-dialkylaminoalkylsubstituent.
In connection with the ongoing work on thiazoles in our laboratory,[9] webecame interested in investigating the aminothiazole system, which would notrearrange under basic reaction conditions. To this end, we surmised synthesizingthe 5-aminothiazoles bearing C-2 substituents with labile hydrogen; this C-2 sub-stituent would react with aqueous sodium hydroxide to form an anion and wouldresist ANRORC activity. We herein report the synthesis of some 2-ethoxycarbony-lamino-5-aminothiazole and related compounds, their unique stability in aqueousalkaline medium, and their thermogravimetric (TG) studies.
RESULTS AND DISCUSSION
Following a published procedure,[10] 2-amino-2-cyanoacetamide was heatedwith N-ethoxycarbonyl isothiocyanate in refluxing ethyl acetate to get 5-amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1) in excellent yield (92.3%)(Scheme 1). The 1H NMR (DMSO-d6) spectral analysis revealed that methyl and
Scheme 1. Synthesis of 5-amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1).
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methylene signals appeared at dH 1.18 and 4.10 respectively. Also, the 13C NMR(DMSO-d6) spectrum analyses revealed that the corresponding carbon signalsappeared at dc 14.45 and 61.47 respectively. In its TG experiment, the compound1 suffered 20.19% loss of mass at �232 �C, corresponding to removal of one ethanolmolecule.
Heating 1 under reflux with an excess of thionyl chloride for 3.5 h, followed byremoval of remaining thionyl chloride under reduced pressure and basification of theresidue with cold aqueous sodium carbonate solution, furnished 5-amino-4-cyano-2-ethoxycarbonylaminothiazole (2) in 71% yield (Scheme 2). The product showedstrong absorptions at 2206.8 (C�N) and 1699.0 (C=O) cm�1 in its infrared (IR;n cm�1, KBr) spectrum. In its 1H NMR and 13C NMR (DMSO-d6) spectra, methyland methylene proton signals were observed at dH 1.18 and 4.10 respectively andtheir carbon signals were observed at dc 14.40 and 61.71 respectively. In the TGexperiment, 2 suffered 23.55% loss of mass at �228 �C, corresponding to removalof one ethanol molecule.
Effect of Refluxing Triethyl Orthoformate on 1, 2, and 5-Amino-1-(x-diethylaminoalkyl)imidazole-4-carboxamides (5, 7)
For the purpose of investigating whether 2-ethoxycarbonylaminothiazolo[5,4-d]pyrimidine-7(6H)-one (4) would respond to similar elimination of ethanol in its TGexperiment, 4 was prepared by heating 1 under reflux with an excess of triethylorthoformate (in the absence of any catalyst, added from outside) in 81% yield(Scheme 2). 1H NMR (DMSO-d6) spectrum analysis revealed that the signals ofH-5 methine and the CH2 and CH3 of the CO2C2H5 moiety appeared at dH 8.40,4.05, and 1.18 respectively. Also, the 13C NMR (DMSO-d6) spectrum analysesrevealed that the corresponding carbon signals appeared at dc159.34, 61.40, and
Scheme 2. Synthesis of 5-amino-4-cyano-2-ethoxycarbonylaminothiazole (2) and thiazolo[5,4-
d]pyrimidine-7(6H)-one (4).
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14.40, respectively. The intermediate product, 5-ethoxymethylenethiazole compound(3), was not isolated as the final product of this uncatalyzed reaction. Unlike this,similar refluxing of 5-amino-1-(3-diethylaminopropyl)imidazole-4-carboxamide (5)in excess triethyl orthoformate furnished 5-ethoxymethyleneamino-1-(3-diethyl-aminopropyl)imidazole-4-carboxamide (6) and refluxing of 5-amino-1-(2-diethyl-aminoethyl)imidazole-1-carboxamide (7) in excess triethyl orthoformate yielded5-ethoxymethyleneamino-1-(2-diethylaminoethyl)imidazole-4-carboxamide (8)(Scheme 3). These reactions, performed with imidazole compounds in absence ofany catalyst, could not close the pyrimidine ring. In its TG experiment, it wasobserved that 4 had suffered 21.87% loss of mass at �327 �C, corresponding to a lossof one ethanol molecule.
Refluxing 2 with an excess of triethyl orthoformate for 2 h furnished 5-ethoxymethyleneamino-4-cyano-2-ethoxycarbonylaminothiazole (9) in 85% yield(Scheme 3). It showed strong absorptions at 2231.1 (C�N) and 1722.9 (C=O)cm�1 in its IR (n cm�1, KBr) spectrum. 1H NMR (DMSO-d6) spectrum analysisrevealed that two methylene proton signals of =CHOCH2CH3 and �COOCH2CH3
appeared as quartets at dH 4.21 and 4.16 respectively, the methyl proton signals app-eared as two overlapped triplets at �dH 1.24, and the methine proton signal appearedat dH 8.37. Also, the 13C NMR (DMSO-d6) spectrum analyses revealed that the meth-ine carbon signal appeared at dc 161.64, two methylene carbon signals appeared at dc62.59 and 62.54, and two methyl carbon signals appeared at dc 14.38 and 14.69; thequaternary C-5, C-4, and C-2 signals appeared at dc 157.61, 104.98, and 144.47respectively. This shows the deshielding effect of EtO-CH=N-substituent at C-5 onthe C-5, C-4, and C-2 signals; this can be compared with the effect of 5-NH2
on C-5, C-4, and C-2 in case of 2, where the signals appear at dc 153.92, 95.40,and 144.19 respectively. In its TG experiment it was observed that 9 hadsuffered 34.24% loss of mass at �212 �C, corresponding to a loss of two ethanolmolecules.
Scheme 3. Effect of triethyl orthoformate on 5-amino-1-(x-diethylaminoalkyl)imidazole-4-carboxamides
(5 and 7) and 5-amino-4-cyano-2-ethoxycarbonylaminothiazole (2).
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Stability of 1 and 2 in Hot Aqueous Alkaline Solution
Compound 1 dissolved in dilute aqueous sodium hydroxide (1.0N) and the sol-ution, after being heated under reflux for 20min, gave back 1 almost quantitatively(�99%) on cooling and acidification with dilute hydrochloric acid.
Similarly, 2 dissolved in cold aqueous sodium hydroxide (1.0N), survivedwarming at 70 �C for 5min, and was recovered unchanged almost quantitatively(�95%) on acidification with cold aqueous hydrochloric acid.
It appears that in alkaline solution the thiazole ring of the anion of 1, and boththe thiazole ring and the cyano group of the anion of 2, can resist any change by theaction of warm alkali because the anions attain stability as shown in Scheme 4.
Thermogravimetric Studies of 1, 2, 4, and 9
Although TG studies have been extensively employed in the field of inorganicchemistry since 1950 and later in the fields of polymer, clays, and mineral chemistry,there are very few reports of its application in the field of organic molecules. Onlyrecently have there been some reports of TG analysis in the fields of organic explo-sives,[11] organic ionic liquids,[12] and a-amino acids.[13] Some work has been reportedon biochemically important heterocyclic compounds[14] and in other importantareas.[15] Because TG studies have been successfully applied to hydrate compoundsof inorganic origin, it was envisaged that a compound with the �NHCO2C2H5
group attached to the C-2 of thiazole ring could respond to characteristic irreversibleelimination of ethanol molecule.
Thermogravimetric studies on 1, 2, 4, and 9 were carried out in a MettlerToledo TGA=SDTA 851 thermal analyzer, in a dynamic atmosphere of dinitrogen(flow rate: 30 cm3min�1) and was programmed with a linear increase of temperatureby 5 �C per min.
Results of Thermogravimetric Experiments on 1, 2, 4, and 9
5-Amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1) underwent a lossof 20.19% at �232 �C corresponding to elimination of 1mol of ethanol (theoretical
Scheme 4. Stability of 5-amino-2-ethoxycarbonylaminothiazole (1) and 5-amino-4-cyano-2-ethoxycarbo-
nylaminothiazole (2) in aqueous alkali.
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loss 20.05%) (Fig. 1). The residue obtained after the TG studies did not melt below300 �C.
5-Amino-4-cyano-2-ethoxycarbonylthiazole (2) underwent a loss of 23.55% at�228 �C corresponding to a loss of 1mol of ethanol (theoretical loss 21.70%) (Fig. 2).
Figure 1. Thermogravimetric scan of 5-amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1).
Figure 2. Thermogravimetric scan of 5-amino-4-cyano-2-ethoxycarbonylaminothiazole (2).
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2-Ethoxycarbonylaminothiazolo[5,4-d]pyrimidine-7(6H)-one (4) underwent aloss of 21.87% at �327 �C corresponding to a loss of 1mol of ethanol (theoreticalloss 19.17%) (Fig. 3).
Figure 3. Thermogravimetric scan of 2-ethoxycarbonylaminothiazolo [5,4-d] pyrimidine-7(6H)-one (4).
Figure 4. Thermogravimetric scan of 5-ethoxymethyleneamino-4-cyano-2-ethoxycarbonylaminothiazole (9).
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5-Ethoxymethyleneamino-4-cyano-2-ethoxycarbonylaminothiazole (9) under-went a loss of 34.24% at �212 �C corresponding to a loss of 2mol of ethanol(theoretical loss 34.33%) (Fig. 4).
A comparision of IR (KBr) absorptions of 1, 2, 4, and 9 with those of therespective residues of TG experiment is given in Table 1. This indicates complete lossof ethanol from the molecules at the characteristic thermal conditions. Additionally,in the 1H NMR (DMSO-d6) spectra of the residues of TG experiments of 1, 2, 4, and9, diagnostic absences of signals at dH 4.0–4.3 and at dH 1.0–1.3 (indicating absenceof CH2 and CH3 respectively of any �OCH2CH3 group) have been observed. Thissupports the view that there has been irreversible loss of ethanol molecule(s) duringthe TG experiments of 1, 2, 4, and 9.
EXPERIMENTAL
The melting points are uncorrected. IR spectra were recorded as KBr pellets ona Perkin-Elmer 782 spectrophotometer. The 1H NMR spectra in DMSO–d6 were runon a Bruker AM-300L instrument operating at 300MHz, and 13C NMR spectrawere run in DMSO–d6 on the same instrument operating at 75.47MHz. The chemi-cal shifts for proton and carbon-13 NMR data are expressed as dH and dC respect-ively. The degrees of proton attachment of the carbons were verified by distortionlessenhancement by polarization transfer (DEPT-135) sequence.
Synthesis of 5-Amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1)
A solution of ethoxycarbonyl isothiocyanate (6.6 g, 0.05mol) was added in oneportion to a solution of 2-amino-2-cyanoacetamide (5.0 g, 0.05mol) in boiling ethylacetate (400mL), and the mixture was heated under reflux for 3h when shining whitecrystals appeared and slowly grew in quantity. The reaction mixture was then cooledin an ice-water bath, and the product was filtered, washed with cold ethyl acetate,and recrystallized from ethanol to get the title compound. White crystalline solid(yield 10.7 g, 92.3%); mp> 310 �C (ethanol). IR (n cm�1, KBr): 3317.0, 3429.2,2708.5, 2904.6, 1703.2; UV (EtOH): kmax (loge) at 283 (3.9); 1H NMR: dH 11.13
Table 1. Comparision of IR (KBr) data of 1, 2, 4, and 9 with those of the corresponding residues of ther-
13CNMR: dc 166.53 (s, CO2Et), 153.97 (s, CONH2), 151.87 (s, C-5), 141.93 (s, C-2),116.36 (s, C-4), 61.47 (t, OCH2), 14.45 (q, CH3). Anal. calcd. for C7H10N4O3S: C,36.52; H, 4.35; N, 24.35%. Found: C, 36.80; H, 4.21; N, 24.16.
Synthesis of 5-Amino-4-cyano-2-ethoxycarbonylaminothiazole (2)
A mixture of 5-amino-2-ethoxycarbonylaminothiazole-4-carboxamide (1)(2.30 g, 0.01mol) and thionyl chloride (15mL) was heated under reflux on ahot-water bath for 3.5 h and cooled. From the reaction mixture, the remaining thio-nyl chloride was removed under reduced pressure. The residue was made alkalinewith cold aqueous sodium carbonate solution. The solid product was filtered andwashed with cold water. White solid (yield 1.51 g, 71%), mp 230–231 �C (ethanol);IR (n cm�1): 3417.2, 3331.0, 3216.2, 2206.8, 1699.0, broad band centered at2936.0; 1H NMR: dH 11.40 (br. s, 1H, NHCO2Et), 6.92 (br. s, 2H, NH2), 4.10 (q,J 7.0Hz, 2H, OCH2), 1.18 (t, J 7.0Hz, CH3);
13C NMR: dC 157.24 (s, CO2Et),116.28 (s, C�N), 144.19 (s, C-2), 95.40 (s, C-4), 153.92 (s, C-5), 61.71 (t, CH2),14.40 (q, OCH2CH3). Anal. calcd. for C7H8N4O2S: C, 39.62; H, 3.77; N, 26.42%.Found: C, 39.40; H, 3.46; N, 26.2.
Synthesis of 5-Ethoxymethyleneamino-1-(x-diethylaminoalkyl)-imidazole-4-carboxamides
A mixture of 5-amino-1-(x-diethylaminoalkyl)imidazole-4-carboxamide(5mmol) and triethyl orthoformate (10mL) was heated under reflux for 2 h and thenthe remaining triethyl orthoformate was removed from the post-reaction mixture byheating at 100 �C under reduced pressure. The residue was triturated with dry diethylether to get the title compound.
Synthesis of 2-Ethoxycarbonylaminothiazolo[5,4-d]pyrimidine-7(6H)-one (4)
A mixture of 5-amino-2-aminothiazole-4-carboxamide (1) (2.3 g, 0.01mol) andtriethyl orthoformate (15mL) was heated under reflux for 3 h. Unreacted triethylorthoformate was removed from the post-reaction mixture by heating at 100 �Cunder reduced pressure to get the title compound. White solid (yield 1.95 g, 81%),mp> 310 �C (ethanol); IR (n cm�1): 3402.7, 3161.7, 2941.1, 1702.8. 1H NMR: dH11.10 (s, 1H, NHCO2Et), 8.40 (1H, s, H-5), 6.70 (s, 1H, N6-H), 4.05 (q, J 6.9Hz,2H, OCH2), 1.18 (t, J 6.9Hz, 3H, OCH2CH3).
Synthesis of 5-Ethoxymethyleneamino-4-cyano-2-ethoxycarbonylaminothiazole (9)
A mixture of 5-amino-4-cyano-2-ethoxycarbonylaminothiazole (2) (1.05 g,5mmol) and triethyl orthoformate (8mL) was heated under reflux for 2 h, andunreacted triethyl orthoformate was removed from the reaction mixture by heatingunder reduced pressure at 100 �C. The reaction mixture was cooled, triturated withdry ether (10mL), and filtered. The residue was recrystallized from ethanol tofurnish the title compound. White solid (yield 1.14 g, 85%); mp 163 �C (ethanol);IR (n cm�1): 3175.9, 2979.0, 2223.1, 1722.9; 1H NMR: dH 8.37 (s, 1H, =CHOEt),4.21 (q, J 7.1Hz, 2H, =CH-O-CH2), 4.16 (q, J 7.1Hz, 2H, CO2CH2), 1.24 (two over-lapped t, 6H, CH=O-CH2CH3 and CO2CH2CH3);
13C NMR: dC 161.64 (d,=CH-OEt), 157.61 (s, CO2Et), 157.51 (s, C-5), 104.94 (s, C-4), 144.47 (s, C-2),114.61 (s, C�N), 62.59 and 62.54 (two t, CO2CH2CH3 and =CH-O-CH2), 14.38(q, CO2CH2CH3), 14.69 (q, =CHOCH2CH3). Anal. calcd. for C10H12N4O3S: C,44.78; H, 4.48; N, 20.90%. Found: C, 44.98; H, 4.27; N, 20.60%.
ACKNOWLEDGMENTS
We thank P. Ghosh for 1H NMR and 13C NMR spectral measurement. One ofthe authors (P. K. Ray) is thankful to the University Grants Commission, NewDelhi, for a research fellowship.
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