C-15-Functionalized Eudesmanolides from Mikania campanulata

Abstract

The aerial parts of Mikania campanulata Gardner afforded the nine new eudesmanolides (1S,4S,5S,6S,7S,10R)-1-hydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (1), (1S,4S,5S,6S,7S,10R)-1,4-dihydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (2), (1R,4S,5S,6S,7S,10R)-1,4-dihydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (3), (1R,4S,5S,6S,7S,10R)-1-hydroxy-4,15-diacetoxyeudesm-11(13)-en-6,12-olide (4), (1S,4R,5S,6S,7S,10R)-1,15-diacetoxy-4-hydroxyeudesm-11(13)-en-6,12-olide (5), (1S,5S,6S,7S,10R)-1-hydroxy-15-acetoxyeudesma-4(15),11(13)-dien-6,12-olide (6), (1S,5S,6S,7S,10R)-1,15-dihydroxyeudesma-3,11(13)-dien-6,12-olide (7a), (1S,2R,5S,6S,7S,10R)-1,2,15-trihydroxyeudesma-3,11(13)-dien-6,12-olide (8a), and (1R,6S,7S,10R)-1,15-dihydroxyeudesma-4,11(13)-dien-6,12-olide (9a), among which the last three were characterized as their corresponding peracetates (7b-9b). The structures of 1-6 and 7b-9b were elucidated using 1D and 2D NMR measurements, while that of major constituent 1 was confirmed by single-crystal X-ray diffraction analysis, and its absolute configuration evidenced from vibrational circular dichroism measurements, which were compared to results obtained from density functional theory calculations. The chemistry of the large genus Mikania is briefly analyzed.

Vibrational Circular Dichroism: A New Tool for the Solution-State Determination of the Structure and Absolute Configuration of Chiral Natural Product Molecules

“…Eudesmanolides. The AC of a series of nine C-15-functionalized eudesmanolides isolated from Mikania campanulata has been reported by Krautmann et al, in collaboration with Joseph-Nathan [56]. The ACs of these molecules were assigned by determination of the AC of 18 (Figure 16) by comparison of the measured and calculated VCDs.…”

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

“…125 The same work also reported the investigation of induced VCD activity in achiral triuoroacetic acid upon interaction with 79 and (+)-cinchonine (80). 128 The related alkaloids (+)-schizogaline (85), (À)-schizogamine (86), and 6,7-dehydro-19b-hydroxyschizozygine (87), isolated from the same species, had their absolute congurations dened by that of 84 assuming a common biosynthetic pathway. 126 The absolute stereochemistry of the pentacyclic core was assigned using NMR and ECD.…”

“…Comparison of experimental VCD with the B3PW91/TZ2P calculated spectrum was considered to provide the most reliable assignment, which was in accordance with previous results obtained via total synthesis. 86 Good agreement between experimental VCD and the spectra calculated at the B3LYP/6-31G(d,p) and B3LYP/DGDZVP levels conrmed the absolute conguration of the diterpene (+)-verticilla-3E,7E-dien-12-ol (29), isolated from Bursera suntui, as 1S,11S,12S. 83 In addition, the highly cytotoxic iridoid (À)-prismatomerin (27), isolated from Primatomeris tetrandra, had its absolute conguration assigned as 1R,5S,8S,9S,10S using VCD and DFT calculations (B3PW91/TZ2P) of its acetate derivative in order to avoid aggregation.…”

In VitroEvaluation of Antiprotozoal and Antiviral Activities of Extracts from ArgentineanMikaniaSpecies

“…Previous reports on the chemical composition of species of the genus Mikania (Asteraceae) describe terpenoid compounds and flavonoids as the main constituents [21–24]. There are some references about the antiprotozoal and antiviral activities of Mikania spp.…”