Six new cassane diterpenes from the twigs and leaves of Tara (Caesalpinia spinosa Kuntze)

• Six new cassane diterpenes were isolated from the twigs and leaves of Tara.
• Compound 3 is an unusual cassane diterpene with unique 6/6/7 carbon rings.
• Compounds 1–5 were evaluated for cytotoxic activity, but they were inactive.

Six new cassane diterpenes, isoneocaesalpin H (1), caespinosin A (2), caespinosin B (3), a cassane diterpene with unique 6/6/7 carbon rings, and caespinosins C–E (4–6) were isolated from the twigs and leaves of Tara (Caesalpinia spinosa Kuntze). The absolute configuration of isoneocaesalpin H (1) was determined by single-crystal X-ray crystallographic analysis. Compound 3 represents a class of rare natural cassane diterpene bearing unique 6/6/7 carbon rings. Their structures were identified by 1D and 2D NMR spectral data. Cassane diterpenes were firstly reported from Tara. Compounds 1–5 were evaluated for their cytotoxicity on HL-60, SMMC-7721, A-549, MCF-7 and SW-480 human cancer cell lines, but they were inactive.

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