Oxygenated Theonellastrols: Interpretation of Unusual Chemical Behaviors Using Quantum Mechanical Calculations and Stereochemical Reassignment of 7α-Hydroxytheonellasterol |
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| Authors: | A-Young Shin Hyi-Seung Lee Yeon-Ju Lee Jong Seok Lee Arang Son Changhoon Choi Jihoon Lee |
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| Institution: | 1.Korea Institute of Ocean Science & Technology (KIOST), Busan 49111, Korea; (A-Y.S.); (H.-S.L.); (Y.-J.L.); (J.S.L.);2.Department of Marine Biotechnology, University of Science & Technology, Daejeon 34113, Korea;3.Department of Radiation Oncology, Samsung Medical Center, Seoul 06351, Korea; (A.S.); (C.C.) |
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| Abstract: | A total of eight new oxygenated 4-exo-methylene sterols, 1–8, together with one artifact 9 and six known sterols 11–16, were isolated from the marine sponge Theonella swinhoei collected from the Bohol province in Philippines. Structures of sterols 1–8 were determined from 1D and 2D NMR data. Among the sterols, 8α-hydroxytheonellasterol (4) spontaneously underwent an allylic 1,3-hydroxyl shift to produce 15α-hydroxytheonellasterol (9) as an artifact; this was rationalized by quantum mechanical calculations of the transition state. In addition, the 1,2-epoxy alcohol subunit of 8α-hydroxy-14,15-β-epoxytheonellasterol (5) was assigned using the Gauge-Independent Atomic Orbital (GIAO) NMR chemical shift calculations and subsequent DP4+ analysis. Finally, comparison of the 13C chemical shifts of isolated 7α-hydroxytheonellasterol (6) with the reported values revealed significant discrepancies at C-6, C-7, C-8, and C-14, leading to reassignment of the C-7 stereochemistry in the known structure. |
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| Keywords: | Theonella swinhoei marine natural product oxygenated theonellasterol GIAO NMR chemical shift calculation anti-inflammatory activity |
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