Bioreduction of Aryl Azides during Mutasynthesis of New Ansamitocins

Abstract

Supplementing a culture of a mutant strain of Actinosynnema pretiosum that is unable to biosynthesize aminohydroxy benzoic acid (AHBA), with 3-azido-5-hydroxy-benzoic acid and 3-azido-5-amino-benzoic acid, unexpectedly yielded anilino ansamitocins instead of the expected azido derivatives. This is the first example of the bioreduction of organic azides. The unique nature of these results was demonstrated when 3-azido-5-amino-benzoic acid was fed to the corresponding AHBA blocked mutant of Streptomyces hygroscopicus, the geldanamycin producer. This mutasynthetic experiment yielded the fully processed azido derivative of geldanamycin.

Evaluation of the Synthetic Potential of an AHBA Knockout Mutant of the Rifamycin Producer Amycolatopsis mediterranei

“…During our investigation of mutasynthetic options with ansamycin antibiotics, we reported on a unique and unprecedented reductive property of the geldanamycin producer S. hygroscopicus towards aryl azides. Selected examples were transformed into the corresponding anilines 19. We have now found that A. mediterranei is the second microbial source able to reduce the bioorthogonal functional azido group (Scheme ).…”

“…Selected examples were transformed into the corresponding anilines. [19] We have now found that A. mediterranei is the second microbial source able to reduce the bioorthogonal functionala zido group (Scheme 3).…”

“…The rifamycinso nly form after reduction of the aryl azide and formation of the pyranone 49 strongly indicates that reductionoft he azido group takes place prior to PKS processing, which would be in line with our studies on the geldanamycin producer S. hygroscopicus. [19,20] Secondly,3-hydroxy-5-nitrobenzoic acid 48 was also converted into rifamycin S 1b in trace amounts, which is the first example of an itroarene being reduced by one of the ansamycin producersino ur hands. A. mediterranei exertedamore impressive reductivepowertowards nitro groups when it was supplemented with 3,5-dinitrobenzoic acid 50.A niline 52 was isolated in asimilarly excellent yield as when 3-amino-5-nitrobenzoic acid 51 was fed to the AHBA(À)m utant strain.…”

Tagging and Enriching Proteins Enables Cell-Specific Proteomics

“…These components are relatively small, and so metabolic precursors modified with azides and alkynes may be tolerated by the natural biosynthetic machinery of cells. However, certain azides are prone to reduction in the cellular milieu ( Mancuso et al., 2013 ), and the reaction between azides and linear alkynes depends on copper (I) catalysis, which requires optimization to avoid damage to biomolecules ( Hong et al., 2009 ). Strain-promoted reactions between azides and strained alkynes remove the copper dependence ( Agard et al., 2004 ).…”

Heat Shock Proteins Revisited: Using a Mutasynthetically Generated Reblastatin Library to Compare the Inhibition of Human and Leishmania Hsp90s

“…The processing of 3,5‐diaminobenzoic acid ( 8 ) is especially remarkable because this mutasynthon can easily form ammonium salts, which would hamper transfer through the membrane of S. hygroscopicus . Indeed, in related cases such as mutasynthetic experiments conducted with the AHBA(−) mutant strain of the ansamitocin producer Actinosynnema pretiosum , feeding of 8 did not yield any mutaproduct …”