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

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.