Elucidation of oxygenation steps during oviedomycin biosynthesis and generation of derivatives with increased antitumor activity

Abstract

Eight different angucyclinones have been produced in Streptomyces albus by combining three oxygenase genes together with the polyketide synthase and cyclases genes from the oviedomycin biosynthetic gene cluster from Streptomyces antibioticus ATCC 11891. Four of these compounds were fully characterized for the first time. Three of these angucyclinones-prejadomycin-2-carboxylate (2), 4a,12b-dehydro-UWM6 (5), and prejadomycin (3)-show a significant increase in their in vitro antitumor activity relative to oviedomycin (1). A hypothesis for the sequence of tailoring events catalyzed by these three oxygenases during oviedomycin biosynthesis is proposed. In this hypothesis OvmOII acts as a bifunctional oxygenase/dehydratase.

Figure 1

Genetic organization of the oviedomycin (ovm) biosynthetic gene cluster; ovm genes are shown in gray. Functions for the corresponding enzymes are oxygenases (OvmOI, OvmOII, and OvmOIII), cyclase (OvmC), keto-acyl synthase α (OvmP), keto-acyl synthase β (OvmK), acyl carrier protein (OvmS), C9-ketoreductase (OvmT), aromatase (OvmA), and 4'-phosphopantetheinyl transferase (OvmF). Below: plasmids used in this work, showing the different gene compositions.

Figure 2

HPLC chromatograms from cell culture extracts of Streptomyces albus strains containing plasmids A) pEM4A, B) pFL1028, C) pFL1031, D) pFL1033, E) pFL1030, F) pFL1146, and G) pFL1223.

Scheme 1

Proposed biosynthetic pathway for oviedomycin; all numbered compounds were isolated and characterized. It is proposed that compounds 7, 8, and 9 are shunt products.

Scheme 2

Prejadomycin-2-carboxylate (2) exists as a tautomeric mixture (data for the minor tautomer 2b are not listed in Table S1 in the Supporting Information).