Stefan Verseck

An Enzyme Module System for the Synthesis of dTDP-activated Deoxysugars from dTMP and Sucrose

A flexible enzyme module system is presented that allows preparative access to important dTDP‐activated deoxyhexoses from dTMP and sucrose. The strategic combination of the recombinant enzymes dTMP‐kinase and sucrose synthase (SuSy), and the enzymes RmlB (4,6‐dehydratase), RmlC (3,5‐epimerase) and RmlD (4‐ketoreductase) from the biosynthetic pathway of dTDP‐β‐L‐rhamnose was optimized. The SuSy module (dTMP‐kinase, SuSy, ±RmlB) yielded the precursor dTDP‐α‐D‐glucose (2) or the biosynthetic intermediate dTDP‐6‐deoxy‐4‐keto‐α‐D‐glucose (3) on a 0.2–0.6 g scale with overall yields of 62 % and 72 %, respectively. A two‐step strategy in which the SuSy module was followed by the deoxysugar module (RmlC and RmlD) resulted in the synthesis of dTDP‐β‐L‐rhamnose (4; 24.1 μmol, overall yield: 35.9 %). Substitution of RmlC by DnmU from the dTDP‐β‐L‐daunosamine pathway of Streptomyces peucetius in this module demonstrated that DnmU acts in vitro as a 3,5‐epimerase with 3 as substrate to yield 4 (32.2 μmol, overall yield: 44.7 %). Chemical reduction of 3 with NaBH4 gave a mixture of the C‐4 epimers dTDP‐α‐D‐quinovose (6) and dTDP‐α‐D‐fucose (7) in a ratio of 2:1. In summary, the modular character of the presented enzyme system provides valuable compounds for the biochemical characterization of deoxysugar pathways playing a major role in microbial producers of antibiotic and antitumour agents.