Thieno[2,3-d]thiazoles were prepared by reaction of 4-chlorothiazole-5carbaldehydes or 4-chlorothiazole-5-carbonittiles with either ethyl 2-mercaptoacetate or 2mercaptoacetamide. The 6-aminothieno[2.3-&hiazole-5-carboxamides obtained were converted into the corresponding thiazolo[4',5';4,5]thieno[3,2-~pyrimidin5(6E?)-one by treatment with triethyl orthoformate in acetic anhydride. With phosphoryl chloride these gave the 5-chloroderivative, which underwent displacement of the chlorine-atom when allowed to react with various amines. Reductive dechlorination of 5-chlorothiazolo[4',5';4,5]thieno[3,2-& pyrimidine gave the parent heterocycle.
Leonard's group2 have synthesised "stretched (or extended) purines" as dimensional probes of enzyme-co-enzyme binding sites. "fin"-extended purines am active, providing that the pyrimidme and imidazole rings are separated by only one other ring (the "spacer unit"), whilst "angular''-extended purines are inactive. As far as we are aware "stretched put&s" in which the "spacer unit" is a heterocyclic ring have not been extensively investigated. Indeed, Leonard2 considers that systems in which the "spacer unit" is a thiophene ring am "good candidates for an analysis of deaminase and oxidase activities". Such systems are neither "linear" nor fully "angular" but "bent" in shape. With this background in mind and because purine analogues are of interest also as potential anticancer and antiviral agents, several years ago we set ourselves the target of synthesising molecules with the general structure 1 (X = CH or N)_3 Progress to date has resulted in the synthesis of several 4-bromoimidazole-5-carbaldehyde& and their conversion into thieno[2,3-d]imidazoles.e We have experienced difficulties in s. ATHMANI and B. bDON
converting these compounds into the target molecules 1 (X = CH). However, in a parallel investigation, which we now describe, we have succeeded in synthesising the novel thiaxole analogues 2 -12.