Inhibition of HSP90 with Pochoximes: SAR and Structure‐Based Insights

The pochoximes, based on the radicicol pharmacophore, are potent inhibitors of heat shock protein 90 (HSP90) that retain their activity in vivo. Herein we report an extended library that broadly explores the structure–activity relationship (SAR) of the pochoximes with four points of diversity. Several modifications were identified that afford improved cellular efficacy, new opportunities for conjugation, and further diversifications. Cocrystal structures of pochoximes A and B with HSP90 show that pochoximes bind to a different conformation of HSP90 than radicicol and provide a rationale for the enhanced affinity of the pochoximes relative to radicicol and the pochonins.     

Potent Inhibition of Acid Sphingomyelinase by Phosphoinositide Analogues

The different mammalian sphingomyelinases are involved in cell regulation, apoptosis and inflammatory events. Recent reports suggest pharmacological potential especially for inhibitors of the acid sphingomyelinase. Phosphatidyl inositol‐3,5bisphosphate (PtdIns3,5P₂) is the most potent selective acid sphingomyelinase inhibitor known to date. In the present study, we synthesized analogues of PtdIns3,5P₂ for initial structure–activity‐relationship (SAR) studies. We identified an inhibitor that is easy to synthesize, that has superior chemical and biophysical properties when compared to PtdIns3,5P₂ and that should be stable against virtually all phospholipases. Last but not least, the new inhibitor partially protected cells from dexamethasone‐induced cell death.     

Biosynthetic Gene Cluster of Cetoniacytone A,an Unusual Aminocyclitol from the Endosymbiotic Bacterium Actinomyces sp. Lu 9419

A gene cluster responsible for the biosynthesis of the antitumor agent cetoniacytone A was identified in Actinomyces sp. strain Lu 9419, an endosymbiotic bacterium isolated from the intestines of the rose chafer beetle (Cetonia aurata). The nucleotide sequence analysis of the 46 kb DNA region revealed the presence of 31 complete ORFs, including genes predicted to encode a 2‐epi‐5‐epi‐valiolone synthase (CetA), a glyoxalase/bleomycin resistance protein (CetB), an acyltransferase (CetD), an FAD‐dependent dehydrogenase (CetF2), two oxidoreductases (CetF1 and CetG), two aminotransferases (CetH and CetM), and a pyranose oxidase (CetL). CetA has previously been demonstrated to catalyze the cyclization of sedoheptulose 7‐phosphate to the cyclic intermediate, 2‐epi‐5‐epi‐valiolone. In this report, the glyoxalase/bleomycin resistance protein homolog CetB was identified as a 2‐epi‐5‐epi‐valiolone epimerase (EVE), a new member of the vicinal oxygen chelate (VOC) superfamily. The 24 kDa recombinant histidine‐tagged CetB was found to form a homodimer; each monomer contains two βαβββ scaffolds that form a metal binding site with two histidine and two glutamic acid residues. A BLAST search using the newly isolated cet biosynthetic genes revealed an analogous suite of genes in the genome of Frankia alni ACN14a, suggesting that this plant symbiotic nitrogen‐fixing bacterium is capable of producing a secondary metabolite related to the cetoniacytones.     

Combinatorial Mutasynthesis of Scrambled Beauvericins,Cyclooligomer Depsipeptide Cell Migration Inhibitors from Beauveria bassiana

Fungal cyclooligomer depsipeptides such as beauvericin, bassianolide, and enniatins display antibiotic, antifungal, insecticidal, broad‐spectrum cancer cell antiproliferative, and cell migration inhibitory activities. We have identified a gene encoding a novel enzyme, ketoisovalerate reductase (KIVR), which is the sole provider of D ‐hydroxyisovalerate (D ‐Hiv), a common precursor for cyclooligomer depsipeptide biosynthesis in Beauveria bassiana. KIVR and related hypothetical oxidoreductases encoded in fungal genomes are similar to ketopantoate reductases but not to D ‐hydroxycarboxylate dehydrogenases. We demonstrate that a KIVR knockout B. bassiana strain can be used for the efficient mutasynthesis of unnatural beauvericin congeners. Simultaneous feeding of precursor analogues enabled the combinatorial mutasynthesis of scrambled beauvericins, some assembled entirely from unnatural precursors. The effects of the introduced structural changes on the antiproliferative and cell migration inhibitory activities of these analogues were evaluated.