Scheme 3. Cyclization scan of oligomers having Trp(5-Br) shifted along the chain (P1 → P4). Pyrroloindoline formation is sensitive to sequence composition and ring size, but favored by 5-bromotryptophan. No pyrroloindoline is formed from P1 isomer 12, whereas P2 and P3 variants 13 and 14 lead to pyrroloindolines 17e and 18c, respectively, as major products. Internal C3 alkylation of the P4 variant leads instead to cyclization of the terminal carboxamide to exo-pyridoindoline 19b. Reaction conditions as in Scheme 2. * Denotes non-isomeric impurity. For detailed product isomer distribution see ESI Fig. S4–S7.† .
