Combined Muta‐ and Semisynthesis: A Powerful Synthetic Hybrid Approach to Access Target Specific Antitumor Agents Based on Ansamitocin P3

Abstract

Access of four new tumor specific folic acid/ansamitocin conjugates is reported that relies on a synthetic strategy based on the combination of mutasynthesis and semisynthesis. Two bromo-ansamitocin derivatives were prepared by mutasynthesis or by a modified fermentation protocol, respectively, that served as starting point for the semisynthetic introduction of an allyl amine linker under Stille conditions. A sequence of standard coupling steps introduced the pteroic acid/glutamic acid/cysteine unit to the modified ansamitocins. All new derivatives, including those that are expected to be generated after internalization of the folic acid/ansamitocin conjugates into the cancer cell and reductive cleavage of the disulfide linkage showed good to strong antiproliferative activity (IC(50) <10 nM) for different cancer cell lines. Finally, the four conjugates were exposed to two cancer cell lines [cervix carcinoma, KB-3-1 (FR+) and lung carcinoma, A-459 (FR-)], the latter devoid of the membrane-bound folic acid receptor (FR-). All four conjugates showed strong antiproliferative activity for the FR+ cancer cell line but were inactive against the FR- cell line. The synthetic strategy pursued is based on the combination of mutasynthesis and semisynthesis and proved to be powerful for accessing new ansamitocin derivatives that are difficult to prepare by total synthesis.

Ansamitocin P3 Depolymerizes Microtubules and Induces Apoptosis by Binding to Tubulin at the Vinblastine Site

“…Consistent with previous studies [5], [12], [49], ansamitocin P3 was found to potently inhibit proliferation of MCF-7 cells with an IC 50 of 20±2 pM. Maytansine has been reported to have an IC 50 of 710 pM in MCF-7 cells [10] indicating that ansamitocin P3 is more potent than its parent molecule, maytansine.…”

Ansamitocin Libraries by Combining Mutasynthesis with Chemical Synthesis; A New Version of Total Synthesis

“…32 The bromo functionality facilitates palladium-catalyzed debromination to afford AP3 derivative 27, which shows similar antiproliferative activity to that of ansamitocin P3 (3). Remarkably, 3-aminobenzoic acid was not efficiently biotransformed into AP3 derivative 27.…”

Preparation of new alkyne-modified ansamitocins by mutasynthesis

“…We extended these studies by combining mutasynthesis and semisynthesis and thus accessed four new tumor specific folic acid/ansamitocin conjugates [28] (Scheme 2). Bromo-ansamitocin 6 was obtained by mutasynthesis and was synthetically modified to the complex folic acid/drug conjugate 7 .…”