Mccrearamycins A-D, Geldanamycin-Derived Cyclopentenone Macrolactams from an Eastern Kentucky Abandoned Coal Mine Microbe

Abstract

Four cyclopentenone-containing ansamycin polyketides (mccrearamycins A-D), and six new geldanamycins (Gdms B-G, including new linear and mycothiol conjugates), were characterized as metabolites of Streptomyces sp. AD-23-14 isolated from the Rock Creek underground coal mine acid drainage site. Biomimetic chemical conversion studies using both simple synthetic models and Gdm D confirmed that the mccrearamycin cyclopentenone derives from benzilic acid rearrangement of 19-hydroxy Gdm, and thereby provides a new synthetic derivatization strategy and implicates a potential unique biocatalyst in mccrearamycin cyclopentenone formation. In addition to standard Hsp90α binding and cell line cytotoxicity assays, this study also highlights the first assessment of Hsp90α modulators in a new axolotl embryo tail regeneration (ETR) assay as a potential new whole animal assay for Hsp90 modulator discovery.

Keywords: Hsp90; ansamycin; axolotl; biomimetic synthesis; regeneration.

Figure 1

A) Chemical structures of representative Gdm-type ansamycins and B) new compounds isolated from Streptomyces sp. AD-23-14. The unique cyclopentenone ring structure of mccrearamycins A–D is highlighted in red.

Figure 2

The impact of [Gdm] on axolotl embryo tail regeneration as determined by the ETR assay (*p <0.005, **p <0.0001, n =4; #: 3 axolotls were dead at day 7; A: DMSO control; B: 0.1 μM; C: 1 μM; D: 2.5 μM; E: 5 μM; F: 10 μM).

Scheme 1

Proposed metal (M²⁺)-mediated benzilic acid rearrangement of the Gdm hydroxyquinone to afford the mccrearamycin cyclopentenone.

Scheme 2

Synthesis of templates 21 and 22.