Abstract
Simplextone E (1), a new metabolite of polyketide origin, was isolated with eight known analogues (2–9) from the South China Sea sponge Plakortis sp. The relative configuration of the new compound was elucidated by a detailed analysis of the spectroscopic data and quantum mechanical calculation of NMR chemical shifts, aided by the newly reported DP4+ approach. Its absolute configuration was determined by the TDDFT/ECD calculation. Simplextone E (1) is proven to be one of the isomers of simplextone D. The absolute configuration at C-8 in alkyl chain of plakortone Q (2) was also assigned based on the NMR calculation. In the preliminary in vitro bioassay, compounds 6 and 7 showed a selective growth inhibitory activity against HCT-116 human colon cancer cells with IC50 values of 8.3 ± 2.4 and 8.4 ± 2.3 μM, corresponding to that of the positive control, adriamycin (IC50 4.1 μM). The two compounds also showed selective activities towards MCF-7 human breast cancer and K562 human erythroleukemia cells while compound 3 only displayed weak activity against K562 cells.
Highlights
Sponges of the genus Plakortis are known to produce structurally diverse and pharmacologically active polyketides [1]
Results and Freshly collectedspecimens specimens of of Plakortis immediately frozen at −20at°C−and this sp.were were immediately frozen
Produced in the quantum mechanical (QM) step of computation of the NMR chemical shift data, and they were submitted to another round of geometry optimization at the density functional level (DFT) in CH3CN IEFPCM
Summary
Sponges of the genus Plakortis are known to produce structurally diverse and pharmacologically active polyketides [1]. This family of polyketides are commonly characterized with a cyclic peroxide [2,3,4,5,6], a penta-lactone [7,8,9,10,11,12,13], or a furano ring [14,15,16] as core structure, and a flexible alkyl chain. 6‐desmethyl‐6‐ethylspongosoritin A (9) [40,41] The structures of these compounds were elucidated by extensive spectroscopic analysis and compared with the reported data.
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