New antioxidant phenylethanol glycosides from Torenia concolor

Abstract

Two new phenylethanol glycosides, phenylethyl-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranoside (torenoside A, 1) and 2′-O-3,4-dihydroxy-β-phenylethoxy-O-α-l-rhamnopyranosyl-(1″ → 3′)-(4′-O-caffeoyl)-β-d-glucopyranoside (torenoside B, 2), along with the 17 known compounds (3–19) were isolated from Torenia concolor. Those structures were established on the basis of spectroscopic analysis including NMR spectroscopic techniques (¹³C, ¹H, ¹H–¹H COSY, HMQC, HMBC, TOCSY, and NOESY). Moreover, phenylethanol glycosides 3–6 exhibited significant antioxidant activities in DPPH radical scavenging assay.

Keywords:

• Torenia concolor
• Scrophulariaceae
• phenylethanol glycosides
• torenoside A
• torenoside B

Acknowledgements

The authors are thankful to Drs Yao-Haur Kuo and Hui-Chi Huang for the bioassay test in the National Research Institute of Chinese Medicine, Taipei, Taiwan.