Isolation and On‐Line LC/CD Analysis of 3,8″‐Linked Biflavonoids from Gnidia involucrata

Abstract

Investigation of the methanol extract of the roots of Gnidia involucrata (Thymelaeaceae) led to the isolation and characterization of two new 3,8″‐biflavonoid diastereoisomers, named GB‐4 (6a) and GB‐4a (6b). Their absolute configurations were determined in mixture by on‐line LC/CD measurements, which also allowed the revision of absolute configurations of the biflavanoids GB‐1 and GB‐2, and the configurational assignment of GB‐3.

A new NMR approach for structure determination of thermally unstable biflavanones and application to phytochemicals from Garcinia buchananii

“…S16, Supporting Information), corresponding to the molecular formula for C 36 H 32 O 17 . The UV spectrum was very similar to the reported biflavanones, and the loss of 162 Da in the high‐collision energy mass spectrum (MS e ) was representative for a hexose unit which yielded the elemental composition of GB‐2 or buchananiflavanone. Further, characteristic mass fragments of m / z 447, 429, 419, 403, 269, and 125 indicated a GB‐2 aglycone, however (Fig.…”

“…The absolute configuration of 4 and 5 were defined by comparison of their experimental and the published ECD curves of (2 R ,3 S ,2″ S ,3″ S )‐ and (2 R ,3 S ,2″ R ,3″ R )‐(iso)manniflavanone, (2 R ,3 S ,2″ R ,3″ R )‐GB‐2, (2 S ,3 R ,2″ R ,3″ R )‐GB‐1 as well as (2 R ,3 S ,2″ R ,3″ R )‐GB‐4 and (2 S ,3 R ,2″ R ,3″ R )‐GB‐4a . The results showed that the ECD curves of 4 and 5 (Fig.…”

“…The structure elucidation of biflavonoids and biflavanones, respectively, is hampered by the spectral complexity at the dimeric level due to the hindered rotation between the monomers around the C➔C and doubling of signals . Therefore, it is proposed to perform elevated temperature NMR measurements to overcome the rotational barrier to obtain a single set of signals .…”

Complete NMR Assignments of the Antibacterial Biflavonoid GB1 from Garcinia kola

“…Similarly, the signals at dϭ82.4, 81.2, 71.7, and 47.3 were assigned to C-2Љ, C-2, C-3Љ, and C-3, respectively. Although its absolute configuration was recently revised, 14) the complete 1 H-and 13 C-NMR data assignments have not yet been reported. [4][5][6][7][8][9][10][11][12] This has been achieved on the basis of the 1 H-detected heteronuclear multiple quantum coherence (HMQC), HMBC, and the rotating frame Overhauser enhancement spectroscopy (ROESY) spectra.…”

“…13) This phenomenon indicated a characteristic of this kind of 3,8Љ-linked biflavanoids. 14) We compared its NMR data obtained at different temperatures including Ϫ50°C, Ϫ30°C, 21°C, 70°C, and 90°C, and in different solvents such as acetone, pyridine, and dimethyl sulfoxide (DMSO). The results support its complicated conformations due to hindered rotation.…”