Polypunctosides E-K: seven new steroidal saponins from Polygonatum punctatum Royle ex Kunth and their nitric oxide production inhibitory activities

Abstract

Polygonatum punctatum Royle ex Kunth is a high-value medicinal plant found in old natural forests. A phytochemical study on the roots of this plant led to the isolation of seven new steroidal saponins including four furostans (1-4) and three furospirostans (5-7). Their structures were elucidated as (25R)-26-O-(β-D-glucopyranosyl)-furost-5-ene-3β,17α,22α,26-tetraol 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (1), (25R)-26-O-(β-D-glucopyranosyl)-furost-5-ene-3β,14α,17α,22α,26-pentaol 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (2), (25R)-26-O-(β-D-glucopyranosyl)-furost-5-ene-22α-methoxy-3β,17α,26-triol 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (3), (25R)-26-O-(β-D-glucopyranosyl)-furost-5-ene-22α-methoxy-3β,17α,26-triol 3-O-[α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)]-[acetoxy-(→ 6)]-β-D-galactopyranoside (4), 26-O-(β-D-glucopyranosyl)-14α,17α-dihydroxynuatigenin 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (5), 26-O-(β-D-glucopyranosyl)-17α-hydroxynuatigenin 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (6), and 26-O-(β-D-glucopyranosyl)-14α-hydroxynuatigenin 3-O-α-L-arabinopyranosyl-(1 → 2)-β-D-glucopyranosyl-(1 → 4)-β-D-galactopyranoside (7) by extensive spectroscopic analyses, including infrared, high-resolution electrospray ionization mass spectrometry, and one- and two-dimensional nuclear magnetic resonance spectroscopy. Compounds 1-7 inhibited nitric oxide production in lipopolysaccharide activated RAW264.7 cells with IC₅₀ values ranging from 41.5 ± 3.2 to 62.2 ± 3.7 µM, compared to 33.8 ± 2.6 µM for the positive control compound L-NMMA.

Keywords: Asparagaceae; Nitric oxide inhibitor; Polygonatum punctatum; Polypunctoside; Steroidal saponin.