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Paper | Special issue | Vol 47, No. 1, 1998, pp.391-396
Published online, 1st January, 1970
DOI: 10.3987/COM-97-S(N)46
Conformational Analysis of Thiosegetalins by Distance Geometry Calculation

Hiroshi Morita, Young Sook Yun, Koichi Takeya, and Hideji Itokawa*

*Department of Pharmacognosy, School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan


Three-dimensional structures in DMSO-d6 of cyclic thiopeptides, thiosegetalins A2, B1 and B2, prepared from segetalins A and B, were determined by distance geometry calculation and restrained energy minimization from NMR data. The backbone structure of thiosegetalin A2, consisting of two β-turns, a β II turn at Trp5-Ala6 and a β VI turn at Val2-Pro3, retains the backbone conformation of segetalin A, both of which showed estrogen-like activity. Whereas, the backbone conformations of cyclic pentapeptides, thiosegetalins B1 and B2 were different from that of the parent compound, segetalin B. The backbone conformations are important for segetalins to show estrogenic activity. Though thionation is a minimal variation of isosteric replacement, it is a useful conformational modification of cyclic peptides.