Conformations of bryonolic acid and its derivatives in CDCl₃ solution by ¹H and ¹³C NMR spectroscopy

Abstract

Comparison of the 'H and I3C chemical shift data of bryonolic acid (D: C-friedoolean-8-en-3~-01-2Y-oic acid) and its derivatives (13 species) revealed that the conformational features of these compounds in CDCI, solution depend on whether the functional groups at C-29 are trigonal, such as COOCH3, or tetrahedral, such as CH,OH. In order to study the conformational features of these two groups of compounds, vicinal coupling constants between the protons on the E rings of the methyl ester of D : C-friedoolean-8-en-29-oic acid, D : C-friedoolean-8-en-29-01 and its acetate were measured. Comparison of the results with the steric geometries to be expected from the molecular mechanics calculation for the E-ring moieties of these derivatives in the S form (D-E rings: boat-boat form) and the F form (D-E rings: chair-chair form) led to the conclusion that the compounds having a trigonal functional group at C-29 mainly adopt the S form, and those having a tetrahedral functional group at C-29 are present as mixtures of the S and F form in equilibrium in the solutions.

Chemical Constituents from Bombacopsis glabra (Pasq.) A. Robyns: Complete ¹H and 13C NMR Assignments and X Ray Structure of 5-Hydroxy-3,6,7,8,4'-pentamethoxyflavone

“…Using two-dimensional NMR techniques (COSY, HMQC and HMBC), it was possible to assign unequivocal the 1 H and 13 C NMR spectra. Some of the 13 C NMR assignments made by us differ slightly from those given by Greca et al, 13 but were in full agreement with the data reported by Kamisato et al 15 Although compound 2 was identified many years ago, only now a complete unambiguous assignment of the 1 H NMR spectrum has been achieved.…”

Relative Population of S-Form and F-Form Conformers of Bryonolic Acid and Its Derivatives in Equilibrium in CDCl3 Solutions.

“…We synthesized 3, 4, 12 and 13 described in previous papers, 3,13) and also 16 derivatives, 2, 5-11 and 14-21. C-29 functional groups of these model compounds were designed to allow us to reveal the effect on the S : F population of C-29 functionality, i.e., whether the functional groups are trigonal or tetrahedral and the identity of the substituents linking to the C-29 carbon atoms.…”

“…Assignments of carbon chemical shifts of 2-21 were done by comparing the shift data with those of the related compounds 3,13) and recording distortion enhancement by polarization transfer (DEPT) and 1 H-detected heteronuclear multiple bond correlation (HMBC) spectra.…”

“…2), i.e., the S-form (D-E rings: boat-boat form) and the F-form (D-E rings: chair-chair form) are possible for bryonolic acid derivatives, that molecules having these conformations co-exist in equilibrium in CDCl 3 solutions, and that their relative populations are greatly affected by the functionality at C-29. 3) Tabata and co-workers found that 1 had anti-allergic activities.…”

“…2), i.e., the S-form (D-E rings: boat-boat form) and the F-form (D-E rings: chair-chair form) are possible for bryonolic acid derivatives, that molecules having these conformations co-exist in equilibrium in CDCl 3 solutions, and that their relative populations are greatly affected by the functionality at C-29. 3) Tabata and co-workers found that 1 had anti-allergic activities. 4) They also showed that the anti-allergic activities were significantly affected by the C-29 functionality; converting the functional group at C-29 from -COOH to -CH 2 OCO-(CH 2 ) 2 COONa raised the activities as much as by tenfold.…”