Amino acids and peptides—II

N-Formyl-dl-tryptophylglycine ester was cyclized to form 3,4-dihydro-β-carboline derivative (II) by means of polyphosphate ester (PPE). In contrast with this, N-acylglycyl-tryptamine (IIIa, b) or -dl-tryptophan ester (IIIc) underwent two-fold cyclodehydration to yield 5H-imidazo[1′.5′:1.2]pyrido[3.4-b]indole derivatives (V), probably by way of 3,4-dihydro-β-carboline-type intermediate (IV).