Total assignment of the ¹³C spectrum of taraxasteryl acetate by ¹³C–¹³C connectivity experiments and determination of the stereochemistry of taraxasterol by X-ray diffraction

Abstract

13C–13C connectivity (INADEQUATE) experiments have been used to reassign the 13C spectrum of taraxasteryl acetate. This shows that there were ten errors in an earlier 13C spectral assignment for this compound. An X-ray diffraction investigation of taraxasterol shows that ring E adopts a slightly distorted boat conformation. It is suggested that severe steric interactions in the chair form force it to adopt this unusual conformation. On the basis of the 1H–1H coupling constants, it is concluded that taraxasteryl acetate adopts a very similar conformation in solution. Crystals of taraxasterol–ethanol solvate are orthorhombic, space group P21,21,21, wih a = 7.447(1) Å, b = 17.637(2) Å, c = 22.269(4) Å, U = 2925 Å3, and Dcalc = 1.07 g cm−3 for Z = 4.

Unambiguous structural and nuclear magnetic resonance spectral characterization of two triterpenoids of Maprouneaguianensis by two-dimensional nuclear magnetic resonance spectroscopy

“…However, there are 1 1 misassignments in the earlier spectral assignments (19). This reinforces our earlier remarks concerning the unreliability of assigning spectra from model compounds (21) and the desirability of having more reliable techniques for 13c spectral assignment (6,21).…”

Triterpenoids

“…Kudzusapogenol A (254), kadzusapogenol B methyl ester (255), and kadzusapogenol C (256) are three new sapogenols from puerariae radix (the dried roots of Puerarza fobata). 164 Other new oleananes include androsacenal (257) from Androsace suxijragijofiu, 6 5 olean-1 3( 18)-ene-2a,3P, 1 latrio1 (258) from Sufviu pinnatu,' c ,~ 2a,3a-dihydroxyolean-l2-en-28-0ic acid (previously reported as its methyl ester) from Euonymus revofutus, 6 7 2 1 ~-cinnamoyloxy-3~-hydroxyolean-12-en-28-oic acid (259) from Enterofobium contorstisifiquum, 3P,6P-dihydroxyolean-18-en-28-oic acid (260) from Orthopterygium huuncuy,I4* and 19-epi-bartogenic acid (261) and anhydrobartogenic acid (262) from Barringtoniu speciosa. 69 The full details of the structural revision of entagenic acid (263), from Entadu phaseofoides, have appeared.…”

“…*~~ Ursane glucosyl esters from Rubus species have been The X-ray crystal structure of taraxasterol shows that ring E has a slightly distorted boat conformation. 257 …”

Structure of a pentacyclic triterpenyl angelate from Loeseliamexicana. 1H 2D-NMR data and stereochemistry

“…As such, mass spectrometry is not a reliable technique for unambiguous structure elucidation of triterpenes (2). Two-dimensional NMR correlation experiments along with other pulsing techniques based on establishing long range couplings (3,4) provide a more reliable method for the total assignment of triterpene structures (5). In this paper we would like to present an example of work where the use of these techniques led to the assignment of the molecular structure of one uncommon triterpenoid derivative from Loeselia mexicana (1).…”