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Glehnia littoralis (G.) FR. SCHMIDT ex MIQUEL (Umbelliferae) is a perennial herb growing on the sandy beaches of eastern Asia. The dried roots of this plant , commonly known as "Bei Sha Shen", are used in traditional Chinese medicine as tonic, antiphlogistic, and mucolytic for the treatment of respiratory and gastrointestinal disorders. Previous investigations resulted in the isolation of coumarins, coumarin glycosides, and polyacetylenes from constituents of the underground parts of G. littoralis, and monoterpenes, polyalcohols from the fruits. On the other hand, it has been reported that this crude drug exhibited several potent pharmacological activities, including stopping cough, dispelling phlegm, antitumor-promotion, antimutation, antitumor, antibacterial and antifungal, analgesic and sedative, inhibition of tyrosinase, and immunosuppressive activities.In this study, we examined the antioxidant activity and prolyl endopeptidase inhibitory activity of G. littoralis, and isolated 6 new compounds, together with 35 known compounds. We here reported their isolation, structure eluciadation, scavenging activities against l,l-diphenyl-2-picrylhydrazyl (DPPH) radicals, and prolyl endopeptidase inhibitory activities.The underground parts of G. littoralis were extracted with ethanol, and the extract was suspended in water, defatted with petroleum ether, then partitioned with EtOAc and BuOH, successively. The EtOAc fraction was chromatographed on a silica gel column to give compounds 1-19, and 25, while the BuOH fraction was separated by a combination of macroreticular resin D101 column chromatography, Sephadex LH-20 column chromatography and preparative TLC to afford compounds 20-41. Among them, the six new compounds, namely glehnilate (17), (-)-secoisolariciresinol 4-O-β-D-glucopyranoside (31), glehlinoside A (32), glehlinoside B (33), glehlinoside C (34), and 4-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranosyloxy]-3-methoxypropiophenone (36), were determined by analysis of their physical and chemical properties, and spectral data. While, the known compounds were identifiedby means of comparison with published data or with authentic samples as: stigmasterol (1), stigmasterol 3-O-β-D-glucopyranoside (2), vanillic acid (3), salicylic acid (4), ferulic acid (5), caffeic acid (6), isoimperatorin (7), psoralen (8), xanthotoxol (9), scopoletin (10), cnidilin (11), bergapten (12), xanthotoxin (13), falcalindiol (14), (8E)-1,8-heptadecadiene-4,6-diyne-3,10-diol (15), 2-[4’-hydroxyphenyl]-glycol mono frans-ferulate (16), adenosine (18), uridine (19), syringin (20), vanillic acid 4-O-β-D-glucopyranoside (21), benzyl β-D-apiofuranosyl-(l 6)-β-D-glucopyranoside (22), icariside D (23), n-butyl a-D-fructofuranoside (24), baihuaqianhuside (25), 4"-hydroxyimperatoin 4"-O-β-D-glucopyranoside (26), bergaptol-O-β-D-glucopyranoside (27), marmesinin (28), (3’R)-hydroxymarmesin 4’-O-β-D-glucopyranoside (29), osthenol-7-O-β-D-gentiobioside (30), citrusin A (35), (-)-secoisolaricinol (37), quercetin (38), isoquercetin (39), rutin (40), and chlorogenic acid (41). Among these, compounds 1-6, 16, 19, 20-21, 23-24, 27, 35, and 37-41 were first identified in G. littoralis. The above compounds can be divided into 7 types as the following: coumarins, coumarin glycosides, polyacetylenes, aromatics, flavonoids, 1,4-diarylbutane lignans, and 8-O-4’ neolignans.In addition, a summary on the methods for determination of the relative and absolute configurations of 8-O-4’ neolignans was carried out.The antioxidant activity of G. littoralis was investigated. The EtOAc-soluble Fr. showed potent activity (EC50= 48.3 ug/ml) in the DPPH radical scavenging assay. Thus we further examined the activities of the above compounds 3, 5-10, 18-19, 25-41, together with the well-known potent antioxidant ascorbic acid. The results showed that the antioxidant activity of G. littoralis was mainly due to the presence of ferulic acid (5), caffeic acid (6), (-)-secoisolariciresinol 4-O-β-D-glucoside (31), glehlinoside A (32), (-)-secoisolariciresinol
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