Chun-Xiao Xu

Enantioselective Total Synthesis of Peloruside A: A Potent Microtubule Stabilizer

An enantioselective total synthesis of (+)-peloruside A (1) is described. Peloruside A (1) is a potent microtubule stabilizer with significant clinical potential. The synthesis is convergent and involves the assembly of C1-C10 segment 2 and C11-C24 segment 3 by a novel aldol protocol followed by Yamaguchi macrolactonization of the resulting seco-acid, selective methylation of hemi-ketal and removal of the protecting groups to peloruside A.

Peloruside B, A Potent Antitumor Macrolide from the New Zealand Marine Sponge Mycale hentscheli: Isolation, Structure, Total Synthesis, and Bioactivity

Peloruside B (2), a natural congener of peloruside A (1), was isolated in sub-milligram quantities from the New Zealand marine sponge Mycale hentscheli. Peloruside B promotes microtubule polymerization and arrests cells in the G(2)/M phase of mitosis similar to paclitaxel, and its bioactivity was comparable to that of peloruside A. NMR-directed isolation, structure elucidation, structure confirmation by total synthesis, and bioactivity of peloruside B are described in this article. The synthesis features Sharpless dihydroxylation, Browns asymmetric allylboration reaction, reductive aldol coupling, Yamaguchi macrolactonization, and selective methylation.

Novel P2 tris-tetrahydrofuran group in antiviral compound 1 (GRL-0519) fills the S2 binding pocket of selected mutants of HIV-1 protease.

GRL-0519 (1) is a potent antiviral inhibitor of HIV-1 protease (PR) possessing tris-tetrahydrofuran (tris-THF) at P2. The high resolution X-ray crystal structures of inhibitor 1 in complexes with single substitution mutants PR(R8Q), PR(D30N), PR(I50V), PR(I54M), and PR(V82A) were analyzed in relation to kinetic data. The smaller valine side chain in PR(I50V) eliminated hydrophobic interactions with inhibitor and the other subunit consistent with 60-fold worse inhibition. Asn30 in PR(D30N) showed altered interactions with neighboring residues and 18-fold worse inhibition. Mutations V82A and I54M showed compensating structural changes consistent with 6-7-fold lower inhibition. Gln8 in PR(R8Q) replaced the ionic interactions of wild type Arg8 with hydrogen bond interactions without changing the inhibition significantly. The carbonyl oxygen of Gly48 showed two alternative conformations in all structures likely due to the snug fit of the large tris-THF group in the S2 subsite in agreement with high antiviral efficacy of 1 on resistant virus.

A Convergent Synthesis of the Proposed Structure of Antitumor Depsipeptide, Stereocalpin A

The total synthesis of the proposed structure of anticancer agent stereocalpin A is described. The synthesis features a diastereoselective synthesis of a 5-hydroxy-2,4-dimethyl-3-oxooctanoic acid unit with asymmetric anti- and syn-aldol reactions as the key steps. Initial cycloamidation led to complete epimerization at the C-11 stereocenter due to unique steric constraints in the 12-membered depsipeptide ring. A late-stage methylation strategy led to the synthesis of the proposed structure of stereocalpin A.

TiCl4-Promoted Tandem Carbonyl or Imine Addition and Friedel–Crafts Cyclization: Synthesis of Benzo-Fused Oxabicyclooctanes and Nonanes

A new and convenient synthesis of benzo-fused 8-oxabicyclo[3.2.1]octane and 9-oxabicyclo[4.2.1]nonane derivatives are described. The reaction involved a TiCl(4)-mediated tandem carbonyl or imine addition followed by a Friedel-Crafts cyclization to provide these functionalized derivatives in good to excellent yields and high diastereoselectivity.