Synthesis of new pyrimido[4,5-d]pyrimidine derivatives from 5-acetyl-6-methyl-4-methylsulfanylpyrimidine-2(1H)-thiones and guanidine

Abstract

Reactions of 5 acetyl 1 aryl(alkyl) 6 methyl 4 methylsulfanylpyrimidine 2(1H) thiones (prepared from diacetylketene N,S acetal) with guanidine afforded 3 alkyl and 3 aryl 7 amino 5 methyl 4 methylidene 3,4 dihydropyrimido[4,5 d]pyrimidine 2(1H) thiones. By products of these reactions (5 acetyl 1 alkyl(aryl) 6 methyl 2 thiouracils) can also be ob tained from the starting pyrimidinethiones and EtONa in EtOH. Pyrimidopyrimidinethiones can react with MeOH at the methylidene group in the presence of MeONa.Key words: diacetylketene N,S acetal, isothiocyanates, 5 acetyl 6 methyl 4 methyl sulfanylpyrimidine 2(1H) thiones, guanidine, condensation, 7 amino 5 methyl 4 meth ylidene 3,4 dihydropyrimido[4,5 d]pyrimidine 2(1H) thiones, 4 alkoxy 7 amino 4,5 dimeth yl 3,4 dihydropyrimido[4,5 d]pyrimidine 2(1H) thiones, 5 acetyl 1 aryl(alkyl) 6 methyl 2 thiouracils.Pyrimido [4,5 d]pyrimidines, which are structurally re lated to pteridines and purines, are of biological interest because of a variety of their pharmacological activity in cluding bronchodilating, 1 antimicrobial, 2,3 antiallergic, 4 antihypertensive effects. 5 In addition, they are phosphod iesterase 1 and dihydrofolate reductase 6 inhibitors.As a next step in our searching for synthetic routes to pyrimido[4,5 d]pyrimidines, 7-12 here we obtained new de rivatives of this heterocyclic system, viz., 3 alkyl and 3 aryl 7 amino 5 methyl 4 methylidene 3,4 dihydrop yrimido[4,5 d]pyrimidine 2(1H) thiones and 4 alkoxy 7 amino 4,5 dimethyl 3,4 dihydropyrimido[4,5 d]pyrimid ine 2(1H) thiones.Earlier, 10 we have demonstrated that diacetylketene N,S acetal 1 prepared from acetylacetone and methyl thio cyanate in the presence of Ni(acac) 2 13 reacts with phenyl isothiocyanate to give 5 acetyl 4 methylsulfanylpyrimid ine 2 thione 2a (Scheme 1). When the MeS group is re placed by an amino group, compound 2a can be used in reactions with dimethylformamide dimethyl acetal (or di ethyl oxalate) and isocyanates to obtain the bicyclic sys tems pyrimido[4,5 d]pyrimidine and pyrido[2,3 d]pyr imidine, respectively. However, we found it interesting to study the possibility of employing bifunctional nucleo philes for a single step synthesis of fused heterocycles from such pyrimidinethiones.In the present work, we studied reactions of pyr imidinethione 2a and similarly prepared thiones 2b,c with guanidine.We found that reactions of pyrimidinethiones 2a,b with guanidine acetate in boiling n butanol in the presence of MeONa give pyrimidopyrimidinethiones 3a,b in 46 and 36% yields, respectively, and 5 acetylthiouracils 4a,b as by products (see Scheme 1). It should be noted that the pyrimidine ring undergoes reconstruction during the reac tion, and compounds 3a,b containing the exocyclic meth ylidene group, instead of the expected products 5a,b, were obtained.Under similar conditions, pyrimidinethione 2c reacts with guanidine to produce compounds 3c and 4c and, unexpectedly, pyrimidopyrimidinethione 6c. Note that the yield of the latter is higher than that of 3c. Obviously, compound 6c is formed b...