A series of novel 1,2,3,5-tetrahydroimidazo[1,2-a]thieno[2,3-d]-, -[3,2,-d]-, and -[3,4-d]pyrimidin-2-one derivatives has been prepared and tested for the activity of inhibiting platelet aggregation in rats in vitro and ex vivo. These compounds were synthesized through the following reactions: sodium borohydride reduction of 2,4-dichlorothienopyrimidines, followed by ethoxycarbonylmethylation and successive amination. Most of the compounds were found to be potent inhibitors of blood and platelet aggregation. Structure-activity relationships have indicated the essential contribution of the lactam structure and lipophilic substituents on the thiophene ring to the effective interaction of the compounds with a receptor site on the platelet. Among the compounds studied, 1,2,3,5,6,7,8,9-octahydro-[1]benzothieno[2,3-d]imidazo[1,2-a]pyrimidin-2-one (9m) exhibited the most favorable activity.
Extensive works have been made of the preparation of six sets of 2-substituted pyrazine 4-oxide and its isomeric new 1-oxide by unambiguous route, and of the reaction between substituted pyrazine mono-N-oxides and a series of halogenation reagents and acylating agents and of nuclear magnetic resonance (NMR), infrared, and ultraviolet spectral investigations in comparison with isomeric N-oxides.
The mass spectra of pyrazine 4‐ and 1‐oxides, their di‐N‐oxides and corresponding pyrazines have been determined. The fragmentations induced by electron impact were examined by means of deuterium labeling and high‐resolution measurements. The most pronounced feature of the spectra was the appearance of M‐16 ion peaks. In the case of the methyl and methoxy derivatives of 1‐oxides, the intensity ratio of M‐17/M‐16 was larger than in the 4‐oxides.
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