Flavonoid glycosides from Persea caerulea. Unraveling their interactions with SDS‐micelles through matrix‐assisted DOSY, PGSE, mass spectrometry, and NOESY

Abstract

Two flavonoid glycosides derived from rhamnopyranoside (1) and arabinofuranoside (2) have been isolated from leaves of Persea caerulea for the first time. The structures of 1 and 2 have been established by H NMR, C NMR, and IR spectroscopy, together with LC-ESI-TOF and LC-ESI-IT MS spectrometry. From the MS and MS/MS data, the molecular weights of the intact molecules as well as those of quercetin and kaempferol together with their sugar moieties were deduced. The NMR data provided information on the identity of the compounds, as well as the α and β configurations and the position of the glycosides on quercetin and kaempferol. We have also explored the application of sodium dodecyl sulfate (SDS) normal micelles in binary aqueous solution, at a range of concentrations, to the diffusion resolution of these two glycosides, by the application of matrix-assisted diffusion ordered spectroscopy (DOSY) and pulse field gradient spin echo (PGSE) methodologies, showing that SDS micelles offer a significant resolution which can, in part, be rationalized in terms of differing degrees of hydrophobicity, amphiphilicity, and steric effects. In addition, intra-residue and inter-residue proton-proton distances using nuclear Overhauser effect build-up curves were used to elucidate the conformational preferences of these two flavonoid glycosides when interacting with the micelles. By the combination of both diffusion and nuclear Overhauser spectroscopy techniques, the average location site of kaempferol and quercetin glycosides has been postulated, with the former exhibiting a clear insertion into the interior of the SDS-micelle, whereas the latter is placed closer to the surface. Copyright © 2016 John Wiley & Sons, Ltd.

The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy

“…As with both the external and internal calibration methods, the SEGWE estimation model has found use in organometallic chemistry as well as in more traditional organic chemistry and in the identification of natural products [245,246]. Its application has tended to be more fragmentary than both internal and external methods where distinct classes of reagents were subjected to concerted, methodical characterisation.…”

Matrix-assisted DOSY

“…The use of SDS micelles as an effective matrix (in a mixed D2O -DMSO-d6 solvent) was demonstrated using a more complex mixture of the flavonoids: flavone, fisetin, (+)catechin and quercetin [114]. Álvarez et al utilised SDS micelles in MAD experiments as part of a larger investigation into two flavonoids from Persea caerulea which differ only in the additional of an extra hydroxyl group and the nature of the carbohydrate moiety [115]. In the absence of SDS micelles the two flavonoids diffuse at the same rate, whereas on addition of 180 mM SDS, quercetin-3-O--Larabinofuranoside shows greater retardation [115].…”

Caerulines A and B, Flavonol Diacylglycosides from Persea caerulea

“…13 We previously reported 14 compounds from this plant, including two tannins, two flavanols, four flavonoid glycosides, one flavonol, two coumarins, and a mixture of three sterols. 8,14 In this context, flavonoids are among the main phytoconstituents of the Persea genus, and among them, flavanols have been identified in several Persea plants. 15−17 In fact, they could be used as taxonomic markers to differentiate species within the Eriodaphne and Persea subgenera.…”