Design, synthesis, and cytotoxicity of stabilized mycolactone analogs

Asymmetric Synthesis of the C15⁻C32 Fragment of Alotamide and Determination of the Relative Stereochemistry

Alotamide is a cyclic depsipetide isolated from a marine cyanobacterium and possesses a unique activation of calcium influx in murine cerebrocortical neurons (EC₅₀ 4.18 µM). Due to its limited source, the three stereocenters (C19, C28, and C30) in its polyketide fragment remain undetermined. In this study, the first asymmetric synthesis of its polyketide fragment was achieved. Four relative possible diastereomers were constructed with a boron-mediated enantioselective aldol reaction and Julia⁻Kocienski olefination as the key steps. Comparison of ¹³C NMR spectra revealed the relative structure of fragment C15⁻C32 of alotamide.

Modular total syntheses of mycolactone A/B and its [2H]-isotopologue

A modular total synthesis of mycolactone A/B, the exotoxin produced by Mycobacterium ulcerans, has been achieved through the orchestration of several Pd-catalyzed key steps. While this route leads to a mixture of the natural product and its C12 epimer (4 : 1 ratio), this was inconsequential from the biological activity standpoint. Compared to the previously reported routes, this synthetic blueprint allows the late-stage modification of the toxin, as exemplified by the preparation of [22,22,22-²H₃]-mycolactone A/B.

The chemistry and biology of mycolactones

Mycolactones are a group of macrolides excreted by the human pathogen Mycobacterium ulcerans, which exhibit cytotoxic, immunosuppressive and analgesic properties. As the virulence factor of M. ulcerans, mycolactones are central to the pathogenesis of the neglected disease Buruli ulcer, a chronic and debilitating medical condition characterized by necrotic skin ulcers. Due to their complex structure and fascinating biology, mycolactones have inspired various total synthesis endeavors and structure-activity relationship studies. Although this review intends to cover all synthesis efforts in the field, special emphasis is given to the comparison of conceptually different approaches and to the discussion of more recent contributions. Furthermore, a detailed discussion of molecular targets and structure-activity relationships is provided.

Synthetic strategies towards mycolactone A/B, an exotoxin secreted by Mycobacterium ulcerans

Pitfalls and dead-ends pave the way to mycolactone A/B. This full account reports synthetic efforts towards this natural product that eventually culminated in a de novo total synthesis.