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The lipid content of Atriplex semibacata growing in Egypt was studied. The unsaponifiable fraction was identified by GLC. A series of hydrocarbons ranging from C14-C28 in addition to cholesterol, stigmasterol and the triterpenoids α and β - amyrin were identified. GLC analysis of fatty alcohols fraction revealed the presence of six fatty alcohols in which dotriacontanol (C32H66O) was the major (14.68%). Six compounds (five coumarins and one phenolic acid) were isolated for the first time from A. semibacata. The coumarin constituents isolated from the chloroform and the ethyl acetate fractions of the aqueous alcoholic extract of A. semibacata were identified as scopoletin, umbelliferorne, coumarin, scopolin, 7-methoxy coumarin in addition to a phenolic acid P-coumaric acid. Also, the flavonoidal compounds isolated from the n-butanol fraction of the plant revealed the presence of kaempferol 3-O glucoside and acacetin. Their identity was proved by m.p., TLC, PC, UV and MS analysis. The alcohol extract showed significant antimicrobial activity against G-ve bacteria, moderate activity against G+ve bacteria. On the other hand, the pet. Ether extract showed marked activity against G+ve bacteria and
fungi, also the G-ve bacteria was greatly inhibited by the chloroform extract. The different extracts of the plant exhibited no cytotoxic activity against Erlich-ascites carcinoma cells line at the tested concentrations, also showed a strong antioxidant activity using DPPH.
Key words: Atriplex semibacata, unsaponifiable fraction, fatty alcohols, coumarins, flavonoids, antimicrobial, antifungal, antioxidant, antitumor.