Stereochemical issues related to the synthesis and reactivity of pyrazino[20 ,10 -5,1]pyrrolo[2,3-b]indole-1,4-diones

Abstract

The cyclization of all four diastereoisomers of cyclo-(Trp-Ala) to the corresponding 3,5a,6,10b,11,11ahexahydro-2H-pyrazino[20 ,10 -5,1]pyrrolo[2,3-b]indoles is studied from the stereochemical point of view. Epimerization of the tryptophan stereocenter during the cyclization and during acylation reactions of the N-2 atom of the tetracyclic derivatives is discussed.