The structure-inhibitory activity relationships were studied in analogous alkaloids from Picrasma quassioides and Ailanthus altissima, and their derivatives. Altogether, 53β- carboline, 18 canthinone and 7 dimeric alkaloids were tested for cyclic adenosine monophosphate (cAMP) phosphodiesterase inhibition. Major alkaloids (10, 63 and 74) among the three groups of congeners in Picrasma quassioides and Ailanthus altissima ...