Three further 1,9-diarylnonanoid 3-O-glycosides from Erica cinerea

In addition to the six diarylnonanoids and diarylnonanoid 3-O-glucosides previously reported from Erica cinerea, the multistep chromatographic processing of the acetone extract of the fresh aerial parts resulted in the isolation of three more representatives as glycosides derived from either (−)-ericanone or (−)-α-ericadione. From the spectroscopic data, the new structures were elucidated as (−)-(3S,7S)-ericanone 3-O-β-d-xylopyranoside, (−)-(3S,7S)-3″-hydroxyericanone 3-O-β-d-glucopyranoside, and (−)-(3S)-3″-hydroxy-α-ericadione 3-O-β-d-glucopyranoside respectively. In the 1H and 13C NMR spectra run in CD3OD, the latter metabolite was as (−)-α-ericadione 3-O-β-d-glucopyranoside, also found as a permanent mixture of the major s-trans (70%) and the minor s-cis (30%) conformers. Such result -in connection with the protic solvent- seems to have never been reported earlier for α-alkadiones. Moreover, mild acid hydrolysis of such a glucoside led directly to the 3,4-dehydrated aglycone moiety accompanied by its 6,7-dehydrated tautomer, according to two successive dehydrations of the anticipated aglycone. Furthermore, although missing in this species, the postulated β-ericadione continues to be regarded as an essential intermediate at the crossroads of the biogenesis of most of the E. cinerea 1,9-diarylnonanoids.

Erica cinerea fresh aerial parts' acetone extract afforded the new 1,9-diarylnonanoid 3-O-glycosides 3, 4, and 9. For the second time, the α-alkadione structural feature is reported in conformational equilibrium in NMR protic solvent.