Chemoenzymatic synthesis of the C10-C23 segment of dictyostatin

[reaction: see text] Employing enzymatic desymmetrization and resolution, respectively, the two aldehydes 8 and 20 were prepared. The precursor to aldehyde 8, meso-2,4-dimethylglutaric anhydride 3, could be obtained by base treatment of the diastereomeric mixture. Aldehyde 8 was extended to alkyne 10 by a Marshall reaction introducing four carbon atoms. Lithiation of the derived iodide 15 and trapping of the anion with amide 22 gave ketone 23. This compound led to the C10-C23 fragment 27 of dictyostatin.