Abstract
Four new anthraquinone derivatives, namely saliniquinones G−I (1–3) and heraclemycin E (4), were obtained from the Antarctic marine-derived actinomycete Nocardiopsis aegyptia HDN19-252, guided by the Global Natural Products Social (GNPS) molecular networking platform. Their structures, including absolute configurations, were elucidated by extensive NMR, MS, and ECD analyses. Compounds 1 and 2 showed promising inhibitory activity against six tested bacterial strains, including methicillin-resistant coagulase-negative staphylococci (MRCNS), with MIC values ranging from 3.1 to 12.5 μM.
Highlights
Saliniquinones are renowned antibiotics featuring a typical anthraquinone-γ-pyrone skeleton [1] and a side chain with different substituents, such as methyl and allyl groups
A comprehensive examination of EtOAc extract using the Global Natural Product Social Molecular Networking (GNPS) platform [6,7], LC-MS-UV, and MarinLit database indicated that the strain N. aegyptia HDN19-252 has potential saliniquinone derivatives in the metabolite profile
Nocardiopsis aegyptia HDN19-252 was cultured in 1 L Erlenmeyer flasks containing 200 g of culture medium composed of 80 g of rice and 120 g of seawater, pH = 7.0 at 28 ◦C for 25 days on stable fermentation
Summary
Saliniquinones are renowned antibiotics featuring a typical anthraquinone-γ-pyrone skeleton [1] and a side chain with different substituents, such as methyl and allyl groups. The absolute configuration of C-15 was determined as 15S based on the CD data, which showed two negative Cotton effects at 267 nm and 372 nm (Figure S4), similar to those of saliniquinone F [1]. Detailed analysis the ECD curve of 1 and saliniquinone C [1] allowed us to draw the conclusion that the negative Cotton effect around 263 nm and 372 nm indicated an S configuration. The overall pattern of the experimental ECD spectrum was in reasonable agreement with the calculated one of (15S, 17S)-2 (Figure 4), indicating the absolute configuration of C-15 and C-17 in 2 as 15S, 17S. The agreement of the experimental and calculated ECD curves (Figure 5) indicated the 15S and 17S absolute configurations of 3.
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