Several simple alkyl and aralkyl derivatives of mesoionic thiazolopyrimidines (1) and mesoionic 1, 3, 4-thiadiazolopyrimidines (2) were found to meas theophylline-like activity as inhibitors of cyclic-AMP phosphodiesterase (PDE). Reduction of the C2-C3 double bond of 1 or replacement of the sulfur atom of 1 or 2 with an N-methyl group nearly abolishes activity. Optimal activity appears to be associated with a hydrophobic substituent at the NB ...
