Retro-aza-Michael reaction of an o-aminophenol adduct in protic solvents inspired by natural products

Mechanistic study of the retro-aza-Michael reaction in saccharothriolide L: identification of 2-amino-4-methylphenol as an effective protecting tool for the Michael acceptor

Saccharothriolide L (1), a derivative of saccharothriolides (STLs) produced by the rare actinomycete Saccharotrix sp. A1506, was synthesized through the precursor-directed in situ synthesis (PDSS) method. The structure of 1 was determined by 1D and 2D NMR and HR-ESI-MS data analyses. A comparison of the rate of the retro-aza-Michael reaction between saccharothriolide L (1) and saccharothriolide B (2) indicated that the 2-amino-4-methylphenol group in 1 might be an effective masking tool for highly reactive, bioactive α, β-unsaturated carbonyl compounds.

Tumescenamide C, a cyclic lipodepsipeptide from Streptomyces sp. KUSC_F05, exerts antimicrobial activity against the scab-forming actinomycete Streptomyces scabiei

The antimicrobial activity of tumescenamide C against the scab-forming S. scabiei NBRC13768 was confirmed with a potent IC50 value (1.5 μg/mL). Three tumescenamide C-resistant S. scabiei strains were generated to compare their gene variants. All three resistant strains contained nonsynonymous variants in genes related to cellobiose/cellotriose transport system components; cebF1, cebF2, and cebG2, which are responsible for the production of the phytotoxin thaxtomin A. Decrease in thaxtomin A production and the virulence of the three resistant strains were revealed by the LC/MS analysis and necrosis assay, respectively. Although the nonsynonymous variants were insufficient for identifying the molecular target of tumescenamide C, the cell wall component wall teichoic acid (WTA) was observed to bind significantly to tumescenamide C. Moreover, changes in the WTA contents were detected in the tumescenamide C-resistant strains. These results imply that tumescenamide C targets the cell wall system to exert antimicrobial effects on S. scabiei.

Formation and Repair of an Interstrand DNA Cross-Link Arising from a Common Endogenous Lesion

Interstrand DNA cross-links (ICLs) are cytotoxic because they block the strand separation required for read-out and replication of the genetic information in duplex DNA. The unavoidable formation of ICLs in cellular DNA may contribute to aging, neurodegeneration, and cancer. Here, we describe the formation and properties of a structurally complex ICL derived from an apurinic/apyrimidinic (AP) site, which is one of the most common endogenous lesions in cellular DNA. The results characterize a cross-link arising from aza-Michael addition of the N²-amino group of a guanine residue to the electrophilic sugar remnant generated by spermine-mediated strand cleavage at an AP site in duplex DNA. An α,β-unsaturated iminium ion is the critical intermediate involved in ICL formation. Studies employing the bacteriophage φ29 polymerase provided evidence that this ICL can block critical DNA transactions that require strand separation. The results of biochemical studies suggest that this complex strand break/ICL might be repaired by a simple mechanism in which the 3'-exonuclease action of the enzyme apurinic/apyrimidinic endonuclease (APE1) unhooks the cross-link to initiate repair via the single-strand break repair pathway.

Identification and Total Synthesis of an Unstable Anticancer Macrolide Presaccharothriolide Z Produced by Saccharothrix sp. A1506

Saccharothriolides A-F are 10-membered microbial macrolides proposed to be generated from their precursors presaccharothriolides X-Z. Previously, we isolated presaccharothriolide X, and its unique natural prodrug-like properties have intrigued us. However, the other congeners were not detected. Herein, we detected presaccharothriolide Z using our highly sensitive labeling reagent. Moreover, chemical synthesis of presaccharothriolide Z, the first total synthesis of saccharothriolide-class macrolides, was achieved, and the structure and biological activity of presaccharothriolide Z were determined.