Substituted derivatives of the hydroxy group at the 2'-or 7'-position in griseolic acid (1) were synthesized by selective substitution in order to study the relationship between structure and inhibitory activity against adenosine 3', 5'-cyclic monophosphate (cAMP) or guanosine 3', 5 '-cyclic monophosphate (cGMP) phosphodiesterase (PDE). All of the derivatives which had a configurationally inverted substituent at the 2'-position instead of the hydroxy group were almost equal to natural griseolic acid in cAMP PDE inhibitory activity, except when the substituent was an amino group. On the other hand, substitution of 7'-OH with inversion tended to reduce the inhibitory activity a little.