Magnolia salicifolia, (Siebold & Zucc.) Maxim. (Siebold & Zucc.) Maxim.

Porter, Elaine A., Kite, Geoffrey C., Veitch, Nigel C., Geoghegan, Ivey A., Larsson, Sonny & Simmonds, Monique S. J., 2015, Phenylethanoid glycosides in tepals of Magnolia salicifolia and their occurrence in flowers of Magnoliaceae, Phytochemistry 117, pp. 185-193 : 186-187

2.1. Phenolic glycosides detected in tepals of M. salicifolia

LC–UV–MS analysis of an 80% CH 3 OH extract of the tepals of M. salicifolia revealed several abundant UV absorbing components ( Fig. 2 ). The UV and serial mass spectra of these suggested they were phenylethanoid glycosides (1–6) and the flavonol glycoside quercetin 3- O -rutinoside. The latter, together with the 3- O -rutinosides of kaempferol and isorhamnetin, present as minor components of the extract, were identified by the mass spectrometry methods described by Kite and Veitch (2011).

The phenylethanoid glycoside 5 was identified as verbascoside by chromatographic and mass spectrometric comparison with a standard. Verbascoside is an acylated glycoside of 3,4-dihydroxyphenylethanol (= hydroxytyrosol; M = 154), the acylating acid being caffeic acid (M = 180). The presence of these two phenolic moieties in 1–4 was suggested from ion trap MS/MS of their doubly deprotonated molecules [M–2H] 2 —, which gave singly charged fragments at m / z 135.0456 (C 8 H 7 O 2), 161.0248 (C 9 H 5 O 3) and 179.0354 (C 9 H 7 O 4), expected for [(hydroxytyrosol–H 2 O)–H] —, [(caffeic acid–H 2 O)–H] — and [caffeic acid–H] —, respectively. Neither 5 nor 6 generated doubly deprotonated molecules but, following ion trap MS/MS, the singly deprotonated molecule of all of 1–6 showed a neutral loss of C9H5O3 (caffeic acid–H 2 O). Collision cell MS2 spectra of deprotonated 1–6 also gave [(caffeic acid–H 2 O)–H] — as the base ion. The sodiated molecules of 1–6 predominately showed a neutral loss of 146 (Rha) following ion trap MS/MS. Compounds 3, 4 and 6 had molecular masses that were each 146 Da greater than 1, 2 and 5, respectively, and the [(M–Rha) + Na] + ion of 3, 4 and 6 generated by MS/MS fragmented by further rounds of serial mass spectrometry in a similar manner to the sodiated molecules of 1, 2 and 5 (see Sections 3.6–3.13). This suggested that compounds 3, 4 and 6 were rhamnosyl derivatives of 1, 2 and 5, respectively.

During the isolation of 1 and 2, two other phenylethanoid glycosides, 1a and 2a respectively, became apparent. Compounds 1a and 2a were present in the initial extract, eluting just before 1 and 2, respectively ( Fig. 2 ), and their molecular masses were 14 Da less than 1 and 2, respectively. The sodiated molecules of 1a and 2a both lost 132 (pentose residue) to give an ion that fragmented in a similar manner to the [(M–Rha) + Na] + ion of 1 and 2, respectively. This suggested 1a and 2a were analogues of 1 and 2 in which the rhamnose at C-3 0 of the core glucose was replaced by a pentose sugar.

Figures

Fig. 2. Maximum absorbance (300–500 nm) chromatograms from LC–UV analyses of 80% CH3OH extracts of Magnolia tepals (top to bottom): M. salicifolia (BI-19354), M. kobus (BI-19363), M. virginiana (BI-19682), M. sieboldii (BI-19731), M. macrophylla (BI-19560), M. delavayi (BI-19737) and M. acuminata (BI-20613). Peaks labelled the phenylethanoid glycosides 1–6 and the 3-O-rutinosides of quercetin (a), kaempferol (b) and isorhamnetin (c). The peak next to 2 in M. virginiana is an isomer of 2 that was not investigated further.