Eleven new mexicanolide-type limonoids, swietmanins A-I (1-4, 7-11), 2-hydroxy-3-O-isobutyrylproceranolide (5), 2-hydroxy-3-O-benzoylproceranolide (6), and a new andirobin-type limonoid, swietmanin J (12), together with 19 known compounds were isolated from the fruits of Swietenia mahagoni. Their structures were established on the basis of spectroscopic methods. These compounds were evaluated against a small panel of microorganisms.

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Sixteen new D-ring-opened phragmalin limonoid orthoesters, swietenitins A-M (1-6, 8, 10, 12-16), 2-acetoxyswietenialide D (7), 2,11-diacetoxyswietenialide D (9), and 11-deoxyswietenialide D (11), and four known compounds were isolated from the twigs of Swietenia macrophylla. The structures of 1-16 were established on the basis of spectroscopic methods, and 1 and 2 were confirmed by single-crystal X-ray diffraction. The (1)H NMR-based conformational analysis on the epimeric compounds 1 and 2 provided a general approach to determine the absolute configuration of the 2,3-epoxy-2-methylbutyryloxy unit at C-3 borne by a large group of the known phragmalin-type limonoid orthoesters.

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Swietenia species of family Meliaceae are mainly found in Malaysia, India and Southeast Asia, and many of them have been applied in traditional medicine. [1][2][3][4][5][6] Recently, we reported the isolation and characterization of sixteen D-ring opened phragmalin-type limonoid orthoesters from the twigs and leaves of Swietenia macrophylla which were collected in Hainan Province of People's Republic of China. 7) In a continuation, eleven new phragmalin-type limonoid orthoesters, swietenitins N-X (1-11), as well as a known one epoxyfebrinin B (12), were further isolated from the same plant sample. The stereochemistry of epoxyfebrinin B (12) was completely assigned in the current study. The antimicrobial activities of these isolates against a small panel of microbes were evaluated, but none of them were active. Herein, we report the isolation and structure elucidation of 1-12. Results and DiscussionSwietenitins N-Q (1-4) and Epoxyfebrinin B (12) Swietenitin N (1), a colorless crystal, had the molecular formula C 39 H 48 O 15 as determined by high resolution-electron ionization-mass spectra (HR-EI-MS) at m/z 756.2970 [M] ϩ (Calcd 756.2993), which was supported by the protonated and sodiated molecular ions at m/z 756 [MϩH] ϩ and 779 [MϩNa] ϩ in the positive mode of electrospray ionization (ESI)-MS, respectively. The IR absorption peaks at 3537 and 1743 cm Ϫ1 implied the presence of hydroxyl and ester carbonyl groups. 13C-NMR and distortionless enhancement by polarization transfer (DEPT) spectra displayed 39 carbon resonances comprising nine methyl (one methoxyl), six methylenes, six sp 3 methines (four oxygenated), nine sp 3 quaternary carbons (six oxygenated), five carbonyl and two double bonds. Furthermore, a combined analysis of its 1 H-and 13 C-NMR data (Tables 1, 2) revealed the presence of one acetyl, an orthoacetate group, a b-furyl ring, a propionyloxy group and an 2,3-epoxy-2-methyl-butyryl moiety. There are sixteen unsaturations in the molecule of 1, of which, nine degrees are occupied by five ester carbonyls, 2,3-epoxy-2-methyl-butyryl moiety and the b-furyl ring, and the remaining seven degrees required 1 being heptacyclic at the central core. The aforementioned data suggested that 1 was a phragmalin-type limonoid orthoester.Extensive analysis of 2D-NMR spectra, especially heteronuclear multiple bond correlation (HMBC), allowed the assignment of the most functional groups to the limonoid core and confirmed the framework of a phragmalin-type limonoid for 1. In the HMBC (Fig. 1A), the key correlations of H 2 -29/C-1, C-2, C-4, C-28 and C-10, and H-30/C-3, C-2, C-8 and C-9 revealed 1 being a B-seco phragmalin-type limonoid. The carbon resonances at d 170.4 and 78.8 were assignable to C-16 and C-17 by the HMBC correlations between H 2 -15 and C-16, and between H 3 -18 and C-17, respectively, indicating the existence of the ring D of a six-membered lactone.8) The quaternary carbon at d 118.8 (C-31) correlating with a methyl at d 1.67 (s) revealed the presence of a typical orthoacetate moiety. The HMBC...

Three new halimane-type diterpenoids formosins A–C (1–3), and three clerodane-type diterpenoids formosins D–F (4–6), were isolated from the twigs of Excoecaria formosana. Their structures were assigned on the basis of spectroscopic data analysis. Compounds 1 and 4 showed moderate anti-microbial activities against Bacillus subtilis (MIC = 50 and 50 μg/mL, respectively). Compound 6 exhibited moderate anti-microbial activities against two strains of Helicobacter pylori (Hp-SS1 and ATCC 43504) with MIC values of 50 and 50 μg/mL, respectively.Graphical abstractElectronic supplementary materialThe online version of this article (doi:10.1007/s13659-016-0086-6) contains supplementary material, which is available to authorized users.

A new compound, named gentianopfluorenone (1), along with three known compounds,1-O-beta-d-glucopyranosyl-5-hydroxy-3-methoxyxanthone (2), 1-O-[beta-d-xylopyranosyl-(1 --> 6)-beta-d-glucopyranosyl]-7,8-dihydroxy-3-methoxyxanthone (3), and apigenin (4), were isolated from the whole herb of Gentianopsis paludosa. On the basis of spectral and chemical evidence, the structure of 1 was elucidated as 4,4a,6-trihydroxy-5-methoxy-fluoren-2,9-dione. Compounds 2-4 were isolated from the plant for the first time.