Abstract
One new bicyclic lactam, cladosporilactam A (1), and six known 12-membered macrolides (2–7) were isolated from a gorgonian-derived Cladosporium sp. fungus collected from the South China Sea. Their complete structural assignments were elucidated by comprehensive spectroscopic investigation. Quantum chemistry calculations were used in support of the structural determination of 1. The absolute configuration of 1 was determined by calculation of its optical rotation. Cladosporilactam A (1) was the first example of 7-oxabicyclic[6.3.0]lactam obtained from a natural source. Compound 1 exhibited promising cytotoxic activity against cervical cancer HeLa cell line with an IC50 value of 0.76 μM.
Highlights
Marine fungi are known for their ability to sequester novel natural products with unique chemical scaffolds possessing a variety of potent biological activities [1]
The individual deviations, |Δδ|, between the predicted and experimental 13C chemical shifts for 1 were less than 5.1 ppm (Table 1), suggesting the δC of 1 matched the calculated δC very well. These results demonstrate that the calculations may be sufficient to confirm the framework for 1
The optical rotations were measured on a JASCO P-1020 digital polarimeter (JASCO Corporation, Tokyo, Japan)
Summary
Marine fungi are known for their ability to sequester novel natural products with unique chemical scaffolds possessing a variety of potent biological activities [1]. The marine-derived Cladosporium fungi have been known to produce various secondary metabolites with novel structures and interesting biological activities such as cytotoxic sporiolides A and B [2], antibacterial Sumiki’s acid (5-hydroxymethylfuran-2-carboxylic acid) [3], and antifouling 3-phenyl-2-propenoic acid [4]. During our ongoing search for structurally novel and bioactive natural products from gorgonians and their symbiotic microorganisms in the South China Sea [5,6,7,8,9,10], we investigated the metabolites of 14 fungal strains cultured from the gorgonian Anthogorgia ochracea by integrated chemical and bioassay screening. We report the isolation, structure elucidation, and bioactivities of these compounds
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