Total synthesis of herbimycin A

Brønsted acid- and Ni(II)-catalyzed C-H oxidation/rearrangement of cyclotriveratrylenes (CTVs) to cyclic and acyclic quinones as potential anti-cancer agents

This paper describes a simple and practical protocol for the direct synthesis of acyclic and cyclic quinone derivatives via an acid-promoted nickel(II)-catalyzed inner rim C-H oxidation of cyclotriveratrylene (CTV) and its analogues. The cyclic quinone derivatives resulted from trimethoxy-cyclotriveratrylene (TCTV) through C-C bond formation via intramolecular ipso substitution followed by subsequent anionic rearrangement containing stereo-vicinal quaternary centers. The DFT calculations strongly support the experimental findings and reveal the role of Brønsted acids in the C-H bond activation of CTV. All the newly synthesized compounds were screened for their in vitro anti-cancer activity using colorimetric SRB assay analysis. Among them, compounds 3a, 3d, 3h, 4a, 4b, 4c and 4e exhibited moderate anticancer activity against A549, HCT-116, PC-3, MDA-MB-231, HEK-293 and SW620 human cancer cell lines.

Total synthesis of proposed elgonene C and its (4R,5R)-diastereomer

The total synthesis of the proposed elgonene C (1) and its (4R,5R)-diastereomer (1a) has been achieved using a second-generation oxazaborolidinium ion-catalysed Diels-Alder reaction, Sharpless asymmetric dihydroxylation, and a Ni-catalysed cross-carboxyl coupling reaction via redox-active ester (RAE) formation as key reactions. The spectral and analytical data for our synthetic compounds 1 and 1a do not match the isolation data provided by Stadler et al. which indicates that structural revision is required for the proposed elgonene C.

Total Synthesis of Geldanamycin

The total synthesis of geldanamycin, a well-known polyketide that exhibited potent anticancer activity by inhibiting Hsp90, was finished in 26 long linear steps with 2.65% overall yield. High convergency of the synthesis was achieved by the disconnection between C12 and C13 that gives C5-C12 and C13-C21 fragments as major building blocks. The use of an alkynyl ketone as the precursor of the C5-C12 fragment enabled a reagent-controlled establishment of C7 chirality and a highly flexible substituent exchange at C8, making the synthetic route suitable for deep-seated structural modifications on geldanamycin.

C15-methoxyphenylated 18-deoxy-herbimycin A analogues, their in vitro anticancer activity and heat shock protein 90 binding affinity

Benzoquinone ansamycins are important leads for the discovery of novel inhibitors of heat shock protein 90 (Hsp90), a promising target of cancer chemotherapeutics. Intrinsic hepatotoxicity caused by the benzoquinone moiety appeared to be a serious limitation to the development of these compounds. To solve this problem by rational structure optimization, a short series of C18-deoxy analogues of herbimycin A were designed based on putative interactions between the compound and the protein. Chemical synthesis of the target molecules were attempted by following the established synthetic route to the natural product, but resulted in the isolation of four serendipitous C15 phenylated final products. In vitro antiproliferative activity and Hsp90 binding affinity of the compounds were determined, suggesting the C18-oxygen of herbimycin A is removable and bulky lipophilic groups can be accommodated at C15 without loss of activity.