SYNTHESES OF MONOCYCLIC AND BICYCLIC PEPTIDES OF TRYPTATHIONINE AND GLYCINE

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Abstract
L-3a-Hydroxy-1.2.3.3a.8.8a-hexahydropyrrolo[2,3-b-]-indole-2-carboxylic acid (Hpi), obtained from L-tryptophan by oxidation with peroxyacetic acid, after introduction of the Boc-residue at N-1, is coupled with various glycine peptides of S-trityl-L-cysteine to give the Hpi-peptides 6(a-f). By treatment with absolute trifluoroacetic acid these peptides are converted by an intramolecular thiolysis to the monocyclic thioethers 7(a-f). Two of them may be subjected to a 2nd cyclization by the mixed anhydride method yielding the bicyclic tryptathionine heptapeptide 8e and octapeptide 8f. In their structures the bicyclic molecules resemble the mushroom phallotoxins and amatoxins, respectively. They show CD [circular dichroism] spectra closely related to the naturally occurring bicyclic peptides indicating conformational similarities. The CD spectra of the other cyclic peptides synthesized were also presented and discussed.