Studies on Thiazolopyridines. Part 1: Antimicrobial Activity of Some Novel Fluorinated Thiazolo[3,2-a]Pyridines and Thiazolo[2′,3′:1,6]Pyrido[2,3-d]Pyrimidines

Ternary condensation of aromatic aldehydes, malononitrile and thioglycolic acid (2:2:1 molar ratio) in ethanol/piperidine afforded the corresponding thiazolo[3,2-a]pyridines 1a-d . Thiazolo[2',3':1,6]pyrido[2,3-d]pyrimidine 4 was obtained by refluxing of compound 1a with acetic anhydride. Also, thiazolopyrido pyrimidine 6 was produced by refluxing of 1a with triethylorthoformate followed by treatment with hydrazine hydrate. Refluxing 1a with formic acid yielded the thiazolopyridopyrimidine 8 which on chlorination with thionyl chloride furnished the chloro derivative 9 . Finally, amino thiazolo[2',3':1,6]pyrido[2,3-d]pyrimidine 10 was obtained by treatment of 1a with formamide. The structures of these compounds were established on the basis of elemental analyses, IR, 1 H NMR, and mass spectral data. Also, the antimicrobial activity of some synthesized compounds is reported.     

Synthesis and Reactions of Polynuclear Heterocycles: Azolothienopyrimidines and Thienothiazolopyrimidines

We prepared a thieno[2,3-d]pyrimidine compound fused with a thiazolo ring to produce biologicaly active compounds. In a one-step reaction, 2-arylmethylene derivative (3) was prepared via the reaction of a ternary mixture of 2-thioxo-1,2,3,4-tetrahydrocyclohepteno[4,5]thieno[2,3-d]pyrimi-dine-4-one (2), cloroacetic acid, and a proper aldehyde. The reaction of 2 with 3-chloropent-2,4-dione in ethanolic potassium hydroxide yielded the S-acetylacetone derivative 4e. The latter compound reacted with hydrazine hydrate and phenyl hydrazine to give 2-pyrazolthio derivatives 8a,b, respectively. Compound 4e also underwent cyclization on boiling with acetic anhydride/pyridine solution to form 2-acetyl-3-methyl thiazolo[3,2-a]cyclohepteno[4,5]thieno[2,3-d] pyrimidine-5-one (9). To support the structure 9, it gave a characteristic reaction for the 2-acetyl group. The 2-methylthio derivatives 4a underwent further alkylation at N₃ to give 6a,b. The purpose of the synthesis of thienopyrimidine derivatives is due to high biological activities. The 4-oxo-thienopyrimidine derivatives acted as inhibitors of adenosine kinase, platelet aggregation, antilukemia, and anticancer activities.     

Synthesis,Characterization and Reactions of 4‐Hydrazino‐2‐methylpyrimidino[4′5′:4,5]thiazolo[3,2‐a]benzimidazole

4‐Hydrazino‐2‐methylpyrimidino[4′,5′:4,5]thiazolo[3,2‐a]benzimidazole ( 4 ) was obtained from hydrazinolysis of the 4‐chloro derivative 3 with hydrazine hydrate. The hydrazino derivative 4 was further cyclized to the corresponding pyrazole 5 , pyrazolone 6 and 5‐methyl‐1,2,4‐triazolo[1″,5″:3′,4′]pyrimidino[5′,6′:5,4]‐thiazolo[3,2‐a]benzimidazole ( 9 ) and 5‐methy‐1,2,4‐triazolo[4″,3″:3′,4′]pyrimidino[5′,6′:5,4]thiazolo‐[3,2‐a]benzimidazole ( 10 ), respectively. The triazolo derivative 10 was isomerized to the triazolo derivative 9 under a variety of reaction conditions.     

Pyrimidinthiones (Part I): Utility of 2-Thioxopyrimidin-6-(1H)ones as Ring Transformer in the Synthesis of Fused Bi- and Tri-Cyclic Heterocyclic Compounds and Their Potential Biological Activities

The pyrimidinethiones have wide biological and pharmaceutical activities, that have attracted considerable interest in recent years especially as antiviral inhibiting production of hepatitis B virus (HBV), and in vitro insulin-mimetic. Activity of the complexes of pyrimidinone derivatives evaluated from 50% inhibitory concentration promoted us to study the transformation of the 2-thioxopyrimidin-6(1H) ones to fused bi- and tri-cyclic heterocyclic compounds having the pyrimidine moieties and screening their biological activity.

The reactivity of 2-mercapto-4-aryl-5-cyanopyrimidin-6(1H)ones (1) towards alkylation by different mono and bifunctional halo-organic compounds has been investigated to give S-monoalkylated products 2, 7 and 9; S- and N-dialkylated products 3, 13 and 14. Treatment of 1 and/or 2 with hydrazine hydrate as a nitrogen nucleophile have been investigated to give 4, treatment of 4 with CS₂ and sodium nitrite in the presence of acetic acid (0°C) produced 1,2,4-triazolopyrimidin-5(1H)one derivatives (5)and tetrazolo[1,5-a]pyrimidin-5(1H)ones (6), respectively. Also cyclization of 7 and 9 gave [1,3]thiazolo[3,2-a]pyrimidin-5(1H)one and [1,3]thiazolo[3,2-a]pyrimidin-3,5-dione derivatives 8 and 10 respectively, treatment of 10 with aromatic aldehyde produces 11 which reacted with guanidine HCl to give pyrimido[4,5-d]thiazolo[3,2-a]pyrimidin-6(1H)one derivative 12. Reaction of 14 with o-phenylenediamine was investigated and gave [1,4]quinoxalino[2,3-b][1,3]thiazolo[3,2-a]pyrimidin-9(1H)one derivative 15.     

Syntheses of some new azolopyrido‐[4′,3′:4,5]thieno[2,3‐d]pyrimidines

Diethyl 2‐[(ethoxythioxomethyl)amino]‐4,5,6,7‐tetrahydrothieno[2,3‐c]‐pyridine‐3,6‐dicarboxylate 2 , prepared from diethyl 2‐isothiocyanato‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3,6‐dicarboxylate 1 by boiling in anhydrous ethanol, was converted into pyrido[4′,3′:4,5]thieno[2,3‐d]pyrimidine derivatives 3, 4 by treatment with hydrazine hydrate. The tetracyclic systems imidazo[1,2‐a]pyrido‐[4′,3′:4,5]thieno[2,3‐d]pyrimidine 9 and pyrido[4′,3′:4,5]thieno[2,3‐d][1,3]thiazolo‐[3,2‐a]pyrimidine 10 were synthesized by the reaction of 2 with 1,2‐diaminoethane and aminoethanethiol, respectively. The hydrazino derivative 4 underwent cyclization reactions with orthoesters and nitrous acid to give the corresponding pyrido[4′,3′:4,5]thieno[2,3‐d][1,2,4]triazolo[1,5‐a]pyrimidines 5, 6 and pyrido[4′,3′:4,5]thieno[3,2‐e][1,2,3,4]tetrazolo[1,5‐a]pyrimidine 8 , respectively. Moreover, reactions of 3 with cyanogen bromide, N‐carbethoxyhydrazine, carbon disulfide, and ethylchloroformate resulted in the formation of the new pyrido[4′,3′:4,5]thieno[2,3‐d][1,3,4]thiadiazolo[3,2‐a]pyrimidine derivatives 12–15 . © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:280–286, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10030     

1,3-Disubstitutedpyrazole-4-caboxaldehyde in Heterocyclic Synthesis: A Novel Synthesis of Pyridine-2(1H)-thione and Fused Nitrogen and/or Sulfur Heterocyclic Derivatives

Pyridine-2(1H)-thione 5 was synthesized from the reaction of 3-[3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl]-1-phenylpropenone (3) and cynothioacetamide (4). Compound 5 reacted with halogented compounds 6a–e to give 2-S-alkylpyridine derivatives 7a–e, which could be in turn cyclized into the corresponding thieno[2,3-b]-pyridine derivatives 8a–e. Compound 8a reacted with hydrazine hydrate to give 9. The latter compound reacted with acetic anhydride (10a), formic acid (10b), acetic acid, ethyl acetoacetate, and pentane-2,4-dione to give the corresponding pyrido[3′,2′:4,5]thieno-[3,2-d]pyrimidine 13a,b, pyrazolo[3′,4′:4,5]thieno[3,2-d]pyridine 14 and thieno[2,3-b]-pyridine derivatives 18 and 20, respectively. Alternatively, 8c reacted with 10a,b and nitrous acid to afford the corresponding pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidine 24a,b and pyrido[3′,2′:4,5]thieno[3,2-d][1,2,3]triazine 26 derivatives, respectively. Finally compound 5 reacted with methyl iodide to give 2-methylthiopyridine derivative 27, which could be reacted with hydrazine hydrate to yield the corresponding pyrazolo[3,4-b]-pyridine derivative 29.     

New data on the alkylation of cyclic thioureas with á-halocarboxylic acids and their esters. 2. Alkylation of tetrahydropyrimidine-2(1h)-thione and 5,5-dimethyltetrahydropyrimidine-2(1h)-thione

In the absence of bases all the attempted variations for the alkylation of tetrahydropyrimidine-2(1H)-thione with á-halocarboxylic acids gave only the bicyclic product-2-R-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidin-3(2H)-one hydrohalide. However the hydrohalide of the “ open” S-ethoxycarbonyl derivative of propyleneisothiourea can be obtained by treatment of tetrahydropyrimidine-2(1H)-thione with ethyl chloro-or bromoacetate in anhydrous acetone at room temperature. Alkylation of 5,5-dimethyltetrahydro-2(1H)-pyrimidinethione with chloro-or bromoacetic acid in anhydrous acetone at room temperature gave the hydrohalide of the “open” S-carboxymethyl derivative of dimethylpropyleneisothiourea. All remaining variations for the alkylation of this substrate with á-halocarboxylic acids or their esters gave only the corresponding bicyclic compounds-the hydrohalide of 2-R-6,6-dimethyl-6,7-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidin-3(2H)-one-independently of the reaction conditions. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 593–604, April, 2006.     

Synthesis and Reactions of 3‐Methylthiazolo[3,2‐a]Benzimidazole‐2‐Carboxylic Acid Hydrazide: Synthesis of Some New Pyrazole, 1,3‐Thiazoline, 1,2,4‐Triazole and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐Thiadiazine Derivatives Pendant to Thiazolo[3,2‐a]Benzimidazole Moiety

The reaction of 3‐methylthiazolo[3,2‐a]benzimidazole‐2‐carboxylic acid ethyl ester (1) with hydrazine hydrate gives the hydrazide 2 which reacts with CS₂/KOH to afford the potassium salt 3. Treatment of 3 with l‐aryl‐2‐bromoethanones 4a,b afforded the 1,3‐thiazoline derivatives 6a,b, respectively, while the reaction of 3 with hydrazine hydrate afforded 1,2,4‐triazole‐3‐thione derivative 9. The reaction of 9 with l‐aryl‐2‐bromoethanones 4a,b and with hydrazonyl chlorides 11a,b gave the 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazine derivatives 10a,b and 12a,b, respectively. Treatment of hydrazide 2 with phenyl isothiocyanate in refluxing benzene gave the thiosemicarbazide derivative 16. The latter reaction gave 1,3,4‐oxadiazole derivative 17 when benzene was replaced by DMF. Cyclization of the thiosemicarbazide derivative 16 with NaOH resulted in the formation of the 1,2,4‐triazole‐3‐thione derivative 18.     

噻唑并嘧啶类化合物的合成研究进展

综述了在医药和农药领域具有广泛用途的噻唑并嘧啶类化合物近二十年来合成方法上的研究进展. 结合本研究组在这一领域的工作介绍了噻唑并嘧啶类化合物的三种主要结构类型: 噻唑并[3,2-a]嘧啶、噻唑并[4,5-d]嘧啶、噻唑并[5,4-d]嘧啶类化合物的相关合成方法及新进展.     

Synthesis and Antibacterial Evaluation of Some New Thiazole‐Based Polyheterocyclic Ring Systems

2‐Cyanoacetamido‐thiazole ( 1 ) was employed as a key for the construction of 6‐cyano‐7‐oxo‐7H‐thiazolo[3,2‐a]pyrimidine ( 4 ) which underwent reaction with hydrazine, malononitrile, ethyl cyanoacetate, and/or various 1,3‐bi‐nuclophilic reagents furnished the corresponding tri‐heterocyclic and tetra‐heterocyclic ring systems 5 – 12 . In addition, the reactions of 1 with various types of arylidene‐malononitriles and/or ethyl 3‐aryl‐2‐cyanoacrylates yielded the corresponding 1‐thiazolyl‐pyridine derivatives 16 and 20 , respectively. Furthermore, treatment of the precursor 1 with carbon disulfide and methyl iodide afforded the ketene dithioacetal derivative 21 which cyclized upon heating with hydrazine and/or 2‐aminobenzimidazole into the corresponding derivatives of N‐(thiazol‐2‐yl)‐1H‐pyrazole‐4‐carboxamide 22 and N‐(thiazol‐2‐yl)benzimidazo[1,2‐a]‐pyrimidine‐3‐carboxamide 23 . The antibacterial properties of these thiazole‐based heterocycles were examined against panel of two bacterial strains.     

One-Pot Synthesis of Novel Spiro Pyrano[2,3-d][1,3]thiazolo[3,2-a]pyrimidine Derivatives

In a one-pot synthesis, 1′-methyl-2,3″-dioxo-5″-aryl-1,2,5a″,7″,8″,9a″-hexahydro-5″H,6″H-dispiro[indole-3,2′-pyrrolidine-3′,2″-pyrano[2,3-d][1,3]thiazolo[3,2-a]pyrimidine]-4′-carboxylic acid methyl ester was prepared via the sequential reaction of 4-aryl-octahydro-pyrano[2,3-d]pyrimidine-2-thione, dimethyl acetylenedicarboxylate (DMAD), and a mixture of isatin and sarcosine. All the novel spiro compounds, in moderate yields, were characterized thoroughly by infrared, NMR, mass spectromentry, and elemental analysis together with x-ray crystallographic analysis.     

Reactions with the Arylhydrazones of α-Cyanoketones: The Structure of 2-Arylhydrazono-3-ketimino-nitriles

Analysis of the IR., UV., and polarographic data of a variety of 2-arylhydrazono-3-ketimino-nitriles indicated that these derivatives exist mainly in the intramolecularly chelated hydrazone structure 1 . Compounds 1 reacted with hydrazine hydrate to yield the corresponding 5-amino-4-arylazopyrazoles ( 3 ). Compounds 3a reacted with acetylacetone, ethyl acetoacetate, and diethyl malonate to yield the pyrazolo[1, 5-a]pyrimidine derivatives 4, 5 , and 7 respectively. Compound 3a also reacted with benzoylisothiocyanate to yield the pyrazolyl thiourea derivative 8 .     

Synthesis of Novel Pyridothienopyrimidines,Pyridothienopyrimidothiazines, Pyridothienopyrimidobenzthiazoles and Triazolopyridothienopyrimidines

The reaction of 3‐amino‐4,6‐dimethylthieno[2,3‐b]pyridine‐2‐carboxamide (1a) or its N‐aryl derivatives 1b‐d with carbon disulphide gave the pyridothienopyrimidines 2a‐d , whilst when the same reaction was carried out using N¹‐arylidene‐3‐amino‐4,6‐dimethylthieno[2,3‐b]pyridine‐2‐carbohydrazides (1e‐h) , pyridothienothiazine 3 was obtained. Also, refluxing of 1b‐d with acetic anhydride afforded oxazinone derivative 4 . Compounds 2a and 2b‐d were also obtained by the treatment of thiazine 3 with ammonium acetate or aromatic amines, respectively. When compound 2a was allowed to react with arylidene malononitriles or ethyl α‐cyanocinnamate, novel pyrido[3″,2″:4′,5′]thieno[3′,2′:4,5]pyrimido[2,1‐b][1,3] thiazines 5a‐c were obtained. Treatment of 2b‐d with bromine in acetic acid furnished the disulphide derivatives 6a‐c . U.V. irradiation of 2b‐d resulted in the formation of pyrido[3″,2″:4′,5′]thieno[3′,2′:4,5]pyrimido[2,1‐b]benzthiazoles 7a‐c . The reaction of 2a‐d with some halocarbonyl compounds afforded the corresponding S‐substituted thiopyrido thienopyrimidines 8a‐j . Compound 8b was readily cyclized into the corresponding thiazolo[3″,2″‐a]‐pyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine 9 upon treatment with conc. sulphuric acid. Heating of 2a,b with hydrazine hydrate in pyridine afforded the hydrazino derivatives 11a,b . Reaction of ester 8c with hydrazine hydrate in ethanol gave acethydrazide 10 . Compounds 10 and 11a,b were used as versatile synthons for other new pyridothienopyrimidines 12–15 as well as [1,2,4] triazolopyridothienopyrimidines 16–19.     

Selective cyclization of S-substituted pyrimidinethione: Synthesis and antimicrobial evaluation of novel polysubstituted thiazolopyrimidine and thiazolodipyrimidine derivatives

The synthetic strategy is based on alkylation of 4-aryl-N-(4-chlorophenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxamide derivatives IV a–g , with some alkyl halides and α-haloketones, namely, methyl iodide, chloroacetonitrile, and phenacyl bromide to give the corresponding S-substituted derivatives Va–c . Treatment of IVa–c with ethyl bromoacetate in ethanol under reflux in the presence of potassium hydroxide solution led to the formation of N-(4-chlorophenyl)-7-methyl-3-oxo-5-(aryl)-2,3-dihydro-5H-thiazolo[3,2-a]pyrimidine-6-carboxamide derivative VIII a–c in a single-step synthesis. On the other hand, compound IVa reacted with α-halo carbonitriles, namely, chloro acetonitrile, and monobromo malononitrile, to produce directly thiazolo[3,2-a]pyrimidine derivatives Xa and Xb , respectively, Compound Xb also reacted with each of formic acid, formamide, and ammonium thiocyanate to form thiazolodipyrimidine derivatives XI–XIII , respectively. Compound VIIIa–c coupled with arenediazonium salts in pyridine to give the corresponding 2-arylhydrazo derivatives XVIa–e . Compounds IV a–g and VIIIa–c were resynthesized under microwave irradiation. Some of the newly synthesized compounds were tested for their antimicrobial activities.     

新型噻唑并[3,2-a]嘧啶类化合物的合成

5-乙氧羰基-4-芳基-6-甲基-3,4-二氢嘧啶-2-酮与丁炔二酸二甲酯反应, 合成了系列新的噻唑并[3,2-a]嘧啶类化合物, 反应具有时间短、收率高、后处理简单等优点. 采用NMR (1H, 13C, COSY, HSQC和HMBC), IR等多种谱学技术, 结合元素分析对产物进行详细表征, 通过对目标产物的1,3-偶极环加成的衍生化产物进行X射线单晶衍射而确定目标产物的结构.     

SYNTHESIS AND REACTIONS OF SOME NEW THIENO[2,3-b]-PYRIDINES AND THE ANTIMICROBIAL EFFECTS

Abstract

3,5-Dicyano-6-mercapto-4-phenylpyridin-2(1H)-one (1) was reacted with ethyl chloroacetate to give compound (II) which on reaction with hydrazine hydrate gave the corresponding hydrazide derivative (III). Acylation of (III) with acetic acid, phenylisocyanate, or phenylisothiocyanate gave different monoacyl derivatives (IV-VI). Condensation of III with aromatic aldehydes and acetylacetone gave compounds VII_a-c, VIII respectively. Compound I was reacted with chloroanilides, bromoacetone and phenacyl bromide to yield the IX-XI; these and compound II gave thieno[2,3-b]-pyridines (XU-XV) on treatment with sodium ethoxide solution. Reaction of XII with acetic anhydride gave the diacetyl derivative XVI. Hydrolysis of compound XII with sodium hydroxide gave the corresponding acid (XVII) which on treatment with acetic anhydride gave the oxazine derivative (XVIII). Reaction of oxazine compound XVIII with ammonium acetate and hydrazine hydrate gave pyrido[3′,2′:4,5] thieno[3,2-d]pyrimidin-4.7-dione derivative (XIX) and (XX) respectively. The N-amino derivative (XX) was reacted with 4-nitrobenzaldehyde to give the corresponding azomethine (XXI).

Significant in vitro gram-positive and gram negative antibacterial activities as well as anti-fungal effect were observed for some members of the series.     

Molecular modeling and cyclization reactions of 2-(4-oxothiazolidine-2-ylidene) acetonitrile

Diazotization of 2-(4-oxothiazolidine-2-ylidene) acetonitrile 1 with aryl diazonium chloride derivatives afforded 4-thiazolidinones 2a, b, whereas 3a, b derivatives produced through reaction of arylcarbonohydrazonoyl dicyanide with thioglycolic acid. Cyclization of 2a with aromatic aldehydes and malononitrile gave the expected substituted thiazolo [3,2-a] pyridines 4a, b. The reaction of 1 with anthraldehyde (1:1 molar ratio) gave the expected 4,5-dihydro-4-oxothiazole derivatives 5 which condensed with other mole p-chlorobenzaldehyde and gave the corresponding bisarylidine derivative 6. Thiazolo [3,2-a] pyridine enaminonitrile derivative 7 produced through addition of malononitrile to bisarylidine 6. Also, compound 7 reacted with other mole of malononitrile and furnished thiazolo [3,2-a] pyridine 12, furthermore, compound 7 refluxed with phenyl hydrazine, thiourea, and formic acid, to form the corresponding thiazolo [3,2-a] pyridines 13, 15 and 17, respectively. Also, compound 1 reacted with phNCS in presence of KOH and afforded 19. The molecular modeling of the synthesized compounds has been drawn and their molecular parameters were calculated. Also, valuable information is obtained from calculation of the molecular parameters including electronegativity, net dipole moment of the compounds, total energy, electronic energy, binding energy, electrophilicity index, HOMO and LUMO energy.     

MgO nanopowders catalyzed synthesis of pyrano[4,3-d]thiazolo[3,2-a]pyrimidine derivatives

A cubic phase of pure MgO nanopowders was prepared in an aqueous solution containing freshly squeezed orange juice with pulp and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FT-IR) spectroscopic techniques. The catalytic potential of MgO nanopowders was evaluated in preparation of pyrano[4,3-d]thiazolo[3,2-a]pyrimidine and chromeno[4,3-d]thiazolo[3,2-a]pyrimidines derivatives using the three simple methods including thermal, ultrasonic irradiation, and high-speed ball milling (HSBM) technique under solvent-free conditions. All products were successfully formed in high yields.     

Synthesis of some novel pyrazolo[1,5-a]pyrimidine derivatives and their application as disperse dyes

A series of novel monoazo-disperse dyes containing pyrazolo[1,5-a]pyrimidine structures were synthesized starting with the coupling reaction between ethyl cyanoacetate and 4-hydroxybenzenediazonium chloride, followed by treatment of the resulting hydrazone product with hydrazine hydrate. The pyrazolohydrazone 6 is then treated with either 2,4-pentandione and enaminonitrile or aryl-substituted enaminoketones to give the target pyrazolo[1,5-a]pyrimidine dyes 7 and 15a-d. Structural assignments to the dyes were made using NMR spectroscopic methods. A new high temperature method, using microwave heating, was employed to apply these dyes to polyester fibers. Most of the dyed fabrics tested displayed moderate light fastness and excellent washing fastness properties.     

A novel heterocyclic compound. Synthesis and reactivities of an oxazolo[3,2-a]thieno[3,2-d]-pyrimidine derivative

A practical preparation of 2,3-dihydro-5H-oxazolo[3,2-a]thieno[3,2-d]pyrimidin-5-one (2) from methyl 3-aminothiophene-2-carboxylate in two steps was developed. The addition reactions of various nucleophiles to 2 were investigated and oxazole-ring-opened compounds were produced (5, 6, 12, 13 and 14). Desulfurization reaction of 2 with Raney Ni gave an oxazolo[3,2-a]pyrimidine derivative (15). It was found that 2 showed potent anti-gastric secretion activity.