Practical synthesis and cytotoxic evaluation of the pyrazino[1,2-b]-isoquinoline ring system

Abstract

A practical three-step protocol for the synthesis of pyrazino[1,2-b]isoquinolines is reported. This approach includes a one-pot parallel cyclization/cyclization parallel process followed by a non-common 6-endo Heck cyclization that transformed previously constructed Ugi adducts into diversely decorated tricyclic systems. Compounds bearing a t-butyl or 2,6-dimethylphenyl substituent showed significant cytotoxic activity. The most active analogue (6p) showed significant activity against HCT-15 and K562 (IC₅₀ = 41.8 ± 3.3 and 57.7 ± 2.1 μM, respectively) with no cytotoxicity against human gingival fibroblasts.