Isolation, stereochemical study, and racemization of (±)‐pratenone A, the first naturally occurring 3‐(1‐naphthyl)‐2‐benzofuran‐1(3H)‐one polyketide from a marine‐derived actinobacterium

Abstract

(±)‐Pratenone A (1), the first representative of natural 3‐(1‐naphthyl)‐2‐benzofuran‐1(3H)‐one polyketides, was isolated from a marine‐derived Streptomyces pratensis strain KCB‐132 together with three other new analogues (2−4). Its structure was assigned by spectroscopic analysis, and the absolute configurations of the two enantiomers separated by high‐performance liquid chromatography were determined by single‐crystal X‐ray diffraction and electronic circular dichroism calculations. The solvent‐induced racemization of 1 and a proposed biogenetic pathway to 1−4 from the co‐isolated angucyclinone precursor, as well as their biological activity, are also discussed.

Recently Discovered Secondary Metabolites from Streptomyces Species

“…Five Streptomyces-derived secondary metabolites containing modified benzofurans were isolated in 2020 from S. pratensis strain KCB-132: (±)-pratenone A (68 and 69), and furamycins I-III (70-72, Figure 19) [40]. The core of these compounds is a benzofuranone ring system linked to naphthalene.…”

“…Furamycin III showed moderate activity against pancreatic cancer cells (IC 50 26.0 µg mL −1 ) and hepatocellular carcinoma (IC 50 42.7 µg mL −1 ) in vitro. Only pratenone A displayed antibacterial activity against S. aureus (MIC 8 µg mL −1 ) [40].…”

“…Furamycin III showed moderate activity against pancreatic cancer cells (IC50 26.0 μg mL −1 ) and hepatocellular carcinoma (IC50 42.7 μg mL −1 ) in vitro. Only pratenone A displayed antibacterial activity against S. aureus (MIC 8 μg mL −1 ) [40]. The final furanic compound reported was 2-alkyl-4-hydroxymethylfuran carboxamide (AHFA, 73), isolated from a soil-derived Streptomyces sp.…”

“…Figure13. The structure of 580-H1(38), 580-H2(39), (2S,2′′S)-6-lavandulyl-7,4′-dimethoxy-5,2′-dihydroxylflavanone(40), (2S,2′′S)-6-lavandulyl-5,7,2′,4′-tetrahydroxylflavanone(41), and (2′′S)-5′-lavandulyl-2′-methoxy-2,4,4′,6′-tetrahydroxylchalcone(42) [29,30].Flavonoids possess a generic structure in which two aromatic rings (A and B) are connected by a heterocyclic pyran. Investigations into bacterial endophytes of the sea sponge Halichondria panicea led to the discovery of Streptomyces sp.…”

“…Figure19. The structures of (±)-pratenone A (68, 69), furamycin I (70), furamycin II (71), furamycin III (72), 2-alkyl-4-hydroxymethylfuran carboxamide (AHFA, 73), and methylenomycin furan (MMF, 74)[40,41].…”