Fig. 4: Chemical preparation of 4 from 13 (isolated from S. albus KR710).
From: Enzymatic spiroketal formation via oxidative rearrangement of pentangular polyketides
Synthesized 4 converts into 12 in aqueous solution at neutral pH, as also observed in the enzyme assays (Fig. 2). Note that the structure of 12 is supported by NMR and IR data, as well as DFT calculations, but a C6-ketohydrate instead of the shown ring-opened compound 12 cannot be ruled out (see Supplementary Fig. 48). Enzymatic steps are indicated with dashed arrows, non-enzymatic chemical steps with bold arrows. A ketoreductase may deter water addition in vivo en route to 1. The stereochemical configuration of 13 and 4/12 is depicted as previously determined for 1 and verified in this work. DMP: Dess–Martin periodinane, DCM: dichloromethane.
