Thirteen limonoids with a new carbon skeleton, the xylogranatins F-R (1-13), have been isolated from the seeds of a Chinese mangrove, Xylocarpus granatum; two recently reported compounds, xylogranatins C and D were also isolated. Their structures were elucidated on the basis of spectroscopic data and chemical methods. The absolute configurations of these compounds were determined by using the modified Mosher MTPA ester method and by quantum chemical circular dichroism (CD) calculations. Xylogranatins F-Q are the first aromatic B-ring limonoids found in nature. They belong to two substructural classes, of which one (1-3) contains a pyridine ring while the other one (4-12) contains a central furan core. Xylogranatins C and R can be considered to be key biosynthetic intermediates, while xylogranatin D, the only limonoid found so far with a carbon skeleton that conatains a C(30)-C(9) linkage, is apparently an artifact. The structures of these compounds suggest a new biogenetic pathway to tetranortriterpenoids. Xylogranatins F, G and R were found to exhibit marked antifeedant activity against the third instar larvae of Mythimna separata (Walker) at a concentration of 1 mg mL(-1). The most potent compound tested was xylogranatin G. Its AFC(50) (concentration for 50 % antifeedant activity) values at the exposure times of 24 and 48 h were 0.31 and 0.30 mg mL(-1), respectively.

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Cortex Pseudolaricis is the root bark of Pseudolarix amabilis Rehder, found only in China, and has been widely used in folk antifungal remedies in traditional Chinese medicine. In order to find the natural antifungal agents against mango anthracnose, eight compounds, namely pseudolaric acid A (1), ethyl pseudolaric acid B (2), pseudolaric acid B (3), pseudolaric acid B-O-β-d-glucoside (4), piperonylic acid (5), propionic acid (6), 3-hydroxy-4-methoxybenzoic acid (7), and 4-(3-formyl-5-methoxyphenyl) butanoic acid (8) were isolated from the ethanol extracts of Cortex Pseudolaricis by bioassay-guided fractionation and evaluated for in vitro antifungal activity against Colletotrichum gloeosporioides Penz. Results demonstrated that all of the eight compounds inhibited the mycelial growth of C. gloeosporioides at 5 μg/mL. Among them, pseudolaric acid B and pseudolaric acid A showed the strongest inhibition with the EC50 values of 1.07 and 1.62 μg/mL, respectively. Accordingly, both Pseudolaric acid B and Pseudolaric acid A highly inhibited spore germination and germ tube elongation of C. gloeosporioides. Dipping 100 μg/mL pseudolaric acid B treatment exhibited more effective suppression on postharvest anthracnose in mango fruit when compared to the same concentration of carbendazim. Scanning electron microscopy observations revealed that pseudolaric acid B caused alterations in the hyphal morphology of C. gloeosporioides, including distortion, swelling, and collapse. Pseudolaric acid B caused the mycelial apexes to show an abnormal growth in dimensions with multiple ramifications in subapical expanded areas with irregular shape. These findings warrant further investigation into optimization of pseudolaric acid B to explore a potential antifungal agent for crop protection.

Three 3beta,8beta-epoxymexicanolides, including xyloccensin K, 6-acetoxycedrodorin and a new one named xyloccensin W, were isolated from the fruit of a Chinese mangrove Xylocarpus granatum. Their structures were determined by spectroscopic analyses. The first complete assignment of (1)H and (13)C NMR data for xyloccensin W was achieved by means of 2D NMR techniques, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectra. In addition, the confusion of (1)H and (13)C NMR data previously reported for xyloccensin K was clarified.

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