Nitric oxide (NO), an inorganic free radical, has been implicated in physiological and pathological process such as vasodilation, non-specific host defence, ischemia reperfusion injury and chronic inflammation. NO is produced by the oxidation of L-arginine by a NO synthase (NOS). In the family of NOS, inducible NOS in particular is involved in a pathological aspect with overproduction of NO, and can be expressed in response to pro-inflammatory agents such as interleukin-1β, tumor necrosis factor-α, and lipopolysaccharide (LPS) in various cells including macrophages, endothelial cells, and smooth muscle cells. In the course of our characterization studies on bioactive constituents of natural medicines, we found that the methanolic or 80% aqueous acetone extract of several fragrance herbal medicines such as Myrrh (the resin of Balsamodendron mukul HOOK.), Olibanum (the resin of Boswellia carrerri BIRDW.), and Saussurea root (the root of Saussurea lappa CLARKE) showed NO production inhibitory activity in LPS-activated macrophages. Through bioassay-guided separation, four new bicyclic triterpene constituents, myrrhanols A and B and myrrhanones A and B were isolated from the methanolic extract of Indian Myrrh together with fourteen known compounds including a progestational hormone, progesterone. On the similar procedure, the 80% aqueous acetone extract of Egyptian Olibanum was purified by various chromatographies to furnish thirteen new terpene constituents named olibanumols A-M together with twenty-nine known compounds such as epilupeol. The stereostructures of their new constituents were elucidated on the basis of chemical and physicochemical evidence. In addition, saussureamines A-E, five new amino acid-sesquiterpne conjugates, were isolated from the methanolic extract of Chinese Saussurea root together with costunolide and dehydrocostus lactone etc. The absolute stereostrucutres of saussureamines A-E were determined on the basis of synthetic evidence. Thus, saussureamins A-E and the related amino acid-sesquiterpene conjugates were synthesized using Michael type addition reaction of amino acid to the α-methylene-γ-lactone moiety of sesquiterpenes. Finally, the isolated constituents such as bicyclic triterpenoids (myrrhanols A and B, myrrhanones A and B) from Myrrh, lupane- and ursane-type triterpenoids and dammarane-type nortriterpenoid (lup-20(30)-ene-3,29-diol, urs-12-ene-3(3β,11α-diol, 3β-hydroxymansumbin-13(17)-ene-l6-one) from Olibanum, and amino acid-sesquiterpene conjugates (saussureamines A and B) from Saussurea root were found to strongly inhibit the NO production. Saussureamines A and B inhibited iNOS induction in accordance with induction of heat shock protein 72 (HSP 72). These results suggested that, as one of their mechanisms of action, amino acid-sesquiterpene conjugates induced HSP 72 thereby preventing nuclear factor-κB activation followed by iNOS induction.
