The N-acyliminium Pictet-Spengler condensation as a multicomponent combinatorial reaction on solid phase and its application to the synthesis of demethoxyfumitremorgin C analogues

[GRAPHICS] L-Tryptophan immobilized on polystyrene-Wang resin was sequentially reacted with an aldehyde and Fmoc-amino acid chloride, This generates a transient N-acyliminium species which undergoes Pictet-Spengler condensation to give a mixture of cis and trans tetrahydro-beta-carbolines. Removal of the Fmoc protecting group, with concomitant diketopiperazine formation, results in c yclative cleavage of the desired products from the resin.