New labdane diterpenoid glycosides from the leaves and flowers of Leucosceptrum canum

Abstract

Four new labdane diterpenoid glycosides, leucanumosides A–D (1–4), were isolated from the leaves and flowers of Leucosceptrum canum. Their structures, sharing an unusual α,β-unsaturated δ-lactone unit, were identified by comprehensive spectroscopic methods, including HRESIMS, NMR, IR, specific rotation, and quantum chemical calculations. The acid hydrolysis method was used to determine the configurations of glycosyl groups. Immunosuppressive assay was performed. Compound 4 exhibited moderate activity against the secretion of cytokines tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in macrophages RAW264.7 induced by lipopolysaccharide (LPS). The plausible biosynthetic pathways for compounds 1–4 were inferred.