Identification by Genome Mining of a Type I Polyketide Gene Cluster from Streptomyces argillaceus Involved in the Biosynthesis of Pyridine and Piperidine Alkaloids Argimycins P

Abstract

Genome mining of the mithramycin producer Streptomyces argillaceus ATCC 12956 revealed 31 gene clusters for the biosynthesis of secondary metabolites, and allowed to predict the encoded products for 11 of these clusters. Cluster 18 (renamed cluster arp) corresponded to a type I polyketide gene cluster related to the previously described coelimycin P1 and streptazone gene clusters. The arp cluster consists of fourteen genes, including genes coding for putative regulatory proteins (a SARP-like transcriptional activator and a TetR-like transcriptional repressor), genes coding for structural proteins (three PKSs, one aminotransferase, two dehydrogenases, two cyclases, one imine reductase, a type II thioesterase, and a flavin reductase), and one gene coding for a hypothetical protein. Identification of encoded compounds by this cluster was achieved by combining several strategies: (i) inactivation of the type I PKS gene arpPIII; (ii) inactivation of the putative TetR-transcriptional repressor arpRII; (iii) cultivation of strains in different production media; and (iv) using engineered strains with higher intracellular concentration of malonyl-CoA. This has allowed identifying six new alkaloid compounds named argimycins P, which were purified and structurally characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. Some argimycins P showed a piperidine ring with a polyene side chain (argimycin PIX); others contain also a fused five-membered ring (argimycins PIV-PVI). Argimycins PI-PII showed a pyridine ring instead, and an additional N-acetylcysteinyl moiety. These compounds seem to play a negative role in growth and colony differentiation in S. argillaceus, and some of them show weak antibiotic activity. A pathway for the biosynthesis of argimycins P is proposed, based on the analysis of proposed enzyme functions and on the structure of compounds encoded by the arp cluster.

From synthetic control to natural products: a focus on N‐heterocycles

“…53 The best enzyme for the racemic resolution was supported lipase from Candida antarctica, which preferentially catalysed acylation of the alcohol with a 3S absolute configuration to provide (+)-3 in 38% yield and 99% enantiomeric excess (e.e.). RuCl 3 (2R,3R)-(−)-5 has also been prepared after acetylation of alcohol (−)-2 using the same approach. Synthesis of cis of 4-hydroxypipecolic acid 13 (and its enantiomer) was similarly carried out by using an efficient chemoenzymatic preparation of a suitable intermediate (Scheme 2).…”

“…111 In this approach, in the presence of a Au(I) catalyst, moiety at position 3 undergo a tandem process that forms pentannulated heterocycles 120 under remarkably mild conditions. 112 Key steps in the process entail the Au(I)-catalysed [3,3]-sigmatropic rearrangement of the propargylic acetate, which generates the requisite pentadienyl cation 119, and Nazarov cyclization of the latter. The synthesis of bruceolline H and I entailed (Scheme 23) Sonogashira coupling of suitably protected iodoindole 124, prepared from commercial 121, to obtain propargylic acetate derivative 126.…”

“…The synthesis of bruceolline H and I entailed (Scheme 23) Sonogashira coupling of suitably protected iodoindole 124, prepared from commercial 121, to obtain propargylic acetate derivative 126. 113 In the presence of the electron-poor [(4-CF 3 C 6 H 4 ) 3 PAu]SbF 6 Au(I) catalyst, this acetate rearranged to generate the required pentadienyl cation with the proper electronic arrangement for Nazarov cyclization. This step provided the cyclopentafused indole 127 in an excellent 82% yield.…”

“…Piperidine and pyrrolidine alkaloids are a major group of natural products isolated from plants or microbes that have been shown to have interesting and diverse bioactivities. [1][2][3] Numerous pharmaceuticals and lead compounds, either synthesized or naturally occurring, contain one or more piperidine units and different patterns of substitution on the heterocycle ring. These alkaloids have been subjected to synthetic studies that have led to the development of new chemosynthetic and biomimetic synthetic methods.…”

Uncovering the unexplored diversity of thioamidated ribosomal peptides in Actinobacteria using the RiPPER genome mining tool

“…Given the absence of a specific protease in the gene cluster, it is plausible that endogenous peptidases are responsible for the liberation of the non-degradable thioamidated APR and GPR tripeptides, which later undergo an Nterminal acetylation catalyzed by an endogenous N-acetyltransferase, as previously reported for other metabolites containing primary amines. 56,57 The timing of VarO-catalyzed dehydrogenation is unclear and could happen directly on the precursor peptide or after proteolysis. Small amounts of thiovarsolins A and B are produced by S. varsoviensis, but the lack of a function for varS and varL suggests that the described thiovarsolins might not be the final products of these pathways.…”