Seventeen new 17-nor-cephalotane-type diterpenoids,
fortalpinoids A–Q (1–17),
were isolated from the seeds of Cephalotaxus fortunei var. alpine. Compound 12 represents
the first 17-nor-cephalotane-type diterpenoid featuring
an 8-oxabicyclo[3.2.1]oct-2-ene moiety. The absolute configuration
of fortunolide A (18) was determined for the first time,
and the structure of cephinoid Q was revised to 14-epi-cephafortoid A (24) by X-ray crystallographic data
analysis. Some of the compounds showed significant cytotoxicity against
A549 and HL-60 cells, and the structure–activity relationship
of this compound class is discussed.
Cephalodiones A–D (1–4), the first example of C19‐norditerpenoid dimers, were isolated and fully characterized from a Cephalotaxus plant. These new skeletal natural products shared a unique tricyclo[6.4.1.12,7]tetradeca‐3,5,9,11‐tetraene‐13,14‐dione core that was capped in both ends with rigid multicyclic ring systems either C2‐symmetrically or asymmetrically. Compounds 1–4 were proposed to be biosynthetically produced by the [6+6]‐cycloaddition of two identical C19‐norditerpenoid troponoids, which was validated by the semisyntheses of dimers 2–4. Moreover, some compounds showed significant inhibition on Th17 cell differentiation.
A chemical investigation of the 95% EtOH extract of the seeds of Cephalotaxus fortunei var. alpina led to the isolation of nine new cephalotane-type norditerpenoids, ceforalides A-I (1-9), and two known analogues (10 and 11). Compounds 1-8 belong to a rare class of A-ring-contracted cephalotane-type norditerpenoids, of which compound 8 incorporates a unique tetrasubstituted 2,5-cyclohexadienone A-ring. Compound 9 is a rare 13,14-seco-17-nor-cephalotane-type diterpenoid. Their structures were determined based on NMR, HRESIMS, ECD, and X-ray diffraction analysis. Biological tests revealed compounds 10 and 11 displayed moderate antimalarial activity.
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