The multiple multicomponent approach to natural product mimics: tubugis, N-substituted anticancer peptides with picomolar activity

The synthesis of a new generation of highly cytotoxic tubulysin analogues (i.e., tubugis) is described. In the key step, the rare, unstable, and synthetically difficult to introduce tertiary amide-N,O-acetal moiety required for high potency in natural tubulysins is replaced by a dipeptoid element formed in an Ugi four-component reaction. Two of the four components required are themselves produced by other multicomponent reactions (MCRs). Thus, the tubugis represent the first examples of the synthesis of natural-product-inspired compounds using three intertwined isonitrile MCRs.

First total synthesis of tubulysin B

The first total synthesis of tubulysin B is described. The aziridine route to tubuphenylalanine (Tup) of the tubulysin D/U-series could not be transferred to the synthesis of tubutyrosine (blue moiety). Therefore, tubutyrosine (Tut) was synthesized by a Wittig olefination/diastereoselective catalytic reduction sequence. Interestingly, the C-2 epimer of tubulysin B has a cytotoxic activity almost identical to the natural diastereomer.