Total Synthesis of the Cyclic Depsipeptide Vioprolide†D via its (Z)-Diastereoisomer.

The first total synthesis of vioprolide D was accomplished in an overall yield of 2.0 % starting from methyl (2S)-3-benzyloxy-2-hydroxypropanoate (16 steps in the longest linear sequence). The cyclic depsipeptide was assembled from two building blocks of similar size and complexity in a modular, highly convergent approach. Peptide bond formation at the C-terminal dehydrobutyrine amino acid of the northern fragment was possible via its (Z)-diastereoisomer. After macrolactamization and formation of the thiazoline ring, the (Z)-double bond of the dehydrobutyrine unit was isomerized to the (E)-double bond of the natural product. The cytotoxicity of vioprolide D is significantly higher than that of its (Z)-diastereoisomer.

Biosynthesis and Heterologous Production of Vioprolides: Rational Biosynthetic Engineering and Unprecedented 4-Methylazetidinecarboxylic Acid Formation.

Vioprolides are a promising class of anticancer and antifungal lead compounds produced by the myxobacterium Cystobacter violaceus Cb vi35. Previously nothing had been reported about their biosynthesis, including the origin of the unusual 4-methylazetidinecarboxylic acid (MAZ) moiety. We describe the vioprolide biosynthetic gene cluster and solve the production obstacle by expression in three heterologous hosts. Starting from unstable production in the wild type at the single-digit mg L-1 scale, we developed a stable host that eventually allowed for yields of up to half a gram per liter in fermenters. Gene inactivations coupled with isotope feeding studies identified an S-adenosylmethionine (SAM)-dependent enzyme and a methyltransferase as being responsible for the generation of the MAZ building block by a proposed mechanism unprecedented in bacteria. Furthermore, nonnatural vioprolide derivatives were generated via rational genetic engineering.

Synthesis and biological evaluation of vioprolide B and its dehydrobutyrine-glycine analogue.

Herein, we describe the total synthesis of the depsipeptide vioprolide B and of an analogue, in which the (E)-dehydrobutyrine amino acid was replaced by glycine. The compounds were studied in biological assays which revealed cytotoxicity solely for vioprolide B presumably by covalent binding to cysteine residues of elongation factor eEF1A1 and of chromatin assembly factor CHAF1A.