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Publikation
Four new 11‐mer peptaibols, named albupeptins A–D (1–4), were isolated from cultures of the fungus Gliocladium album. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopy, as well as ESI‐HRMSn analysis. The sequence of albupeptin A (1) was thus identified as Ac‐Aib1‐Aib2‐Val3‐Leu4‐Aib5‐Pro6‐Iva7‐Leu8‐Gln9‐Aib10‐Leuol11. Albupeptins B (2) and C (3) feature an exchange of Aib5 by Iva5 and of Aib1 by Iva1, respectively, and albupeptin D (4) contains both Iva1 and Iva5 residues. The stereochemistry of the isolated peptaibols 1–4 was unambiguously assigned by 1H NMR chemical shift analysis in conjunction with solid‐phase peptide synthesis. By using this approach, the absolute configuration of the Iva residues in albupeptins A (1) and C (3) was determined to be D, whereas albupeptins B (2) and D (4) feature an additional Iva5 residue with an L configuration. Thus, albupeptins B (2) and D (4) belong to the rare class of peptaibols that have both stereoisomers of Iva in the same sequence.
Publikation
Two novel alkaloidal glucosides derived from the recently discovered antidesmone (1 ), together with four known megastigmane and three lignan glucosides, two of which had not previously been described, were isolated from 1‐butanol extracts of Antidesma membranaceum (Euphorbiaceae). The structural elucidation of (17RS )‐17‐(β‐D ‐glucopyranosyloxy)antidesmone (2 ) and (17RS )‐8‐deoxo‐17‐(β‐D ‐glucopyranosyloxy)antidesmone (3 ) is based on 1H, 13C, COSY, NOESY, HMQC and HMBC NMR spectra, together with LC/ESI‐CIDMS and CD data. Determination of the absolute configuration at C‐17 was accomplished by comparison with 1H NMR spectroscopic data for alk‐2‐yl β‐D ‐glucopyranosides, an approach that also proved useful for the megastigmane glucosides blumenyl C β‐D ‐glucopyranoside (4 ), 3‐oxo‐α‐ionyl β‐D ‐glucopyranoside (5 ), blumenyl B β‐D ‐glucopyranoside (6 ) and blumenyl A β‐D ‐glucopyranoside (7 ). The lignan glucosides lyoniresin‐4‐yl β‐D ‐glucopyranoside (8 ), 4′‐O‐methyllyoniresin‐4‐yl β‐D ‐glucopyranoside (9 ) and secoisolariciresin‐4‐yl β‐D ‐glucopyranoside (10 ), featuring an unusual glucosylation position, were investigated with the aid of 1H and 2D NMR, CD and MS data.