A bioassay-guided fractionation of an ethanol extract of the seeds of Aesculus chinensis led to the isolation of two new flavanoids (1 and 2), along with eight known ones (3-10). The structures of the new compounds were elucidated by spectroscopic methods including 2D NMR. All compounds were tested for antiviral activity against respiratory syncytial virus (RSV), parainfluenza virus type 3 (PIV 3), and influenza virus type A (Flu A). Compounds 1, 2, and 6 showed significant antiviral activities against RSV with IC(50) values of 4.5, 6.7, and 4.1 microg/mL and selective index (SI) values of 15.8, 32, and 63.8, respectively. Compound 8 demonstrated significant antiviral activity against Flu A with an IC(50) of 24.5 microg/mL and a SI of 16.0, respectively.

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Aesculus chinensis BGE. (Hippocastanaceae) is a medicinal plant widely distributed in midwestern China. According to the theory of traditional Chinese medicine, its dried ripe seeds (Suoluozi) have been used as a carminative, stomachic, and analgesic for the treatment of distention and pain in the chest and abdomen.1) The saponin mixture extracted from the seeds of the horse chestnut tree (A. hippocastanum L.) is known as escin, which is almost the same in its constituents as extracted from the seeds of A. chinensis BGE. The total saponins have antiinflammatory, antiedema, capillary protective, hypoglycemic, and ethanol absorption inhibitory activities, 2,3) and therefore the isolation and structure determination of saponin constituentes from aesculus plants have been the targets of many investigations. Although many saponin constituents of escin have been characterized and their activities have been investigated, the main saponins were merely compared and of their antiinflammatory activities in animal experiments reported.In the course of our search for new antiinflammatory agents, one new and five known saponins were obtained from the seeds of A. chinensis BGE. Among them, the four main saponins (escin Ia, escin Ib, isoescin Ia, isoescin Ib) were prepared on a large scale and their antiinflammatory activities investigated in mice. Here we describe the isolation and structural elucidation of a novel triterpenoid saponin, aesculiside A (6), and comparative studies of the antiinflammatory the four main saponins. Results and DiscussionThe 95% EtOH extracts of Suoluozi were separated as described in Experimental to yield compounds 1-6. The five known compounds were identified as 21 C-NMR signals of 6 showed a close resemblance to those of 1 and 5, which were compared with data reported in the literature. 6)Alkaline hydrolysis of 6 with 10% aqueous potassium hydroxide in 50% aqueous dioxane (1 : 1) liberated a substance that had the same retention time as authentic desacylescin I * To whom correspondence should be addressed. (aesculiside A, 6). The antiinflammatory activities of the four main saponins (1-4) were compared with those of total saponin extracts, and single saponins showed more potent activity than total saponin extracts in mice.

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