Nos lO/ll

Abstract: The aryl groups are easily converted to the carboxyl group by oxidation with ruthenium tetroxide. Utilizing this transformation as a key step, several phytosiderophores (mugineic acid (l), 3-epi-hydroxymugineic acid (2), 2'-hydroxynicotianamine (3), and distichonic acid A (4)) and polyoxamic acid (S), the side chain moiety of the antifungal antibiotics polyoxins, have been efficiently and stereoselectively synthesized Reactivity and water solubility of the carboxyl group sometimes preclude the efficient and convenient synthesis of some natural products having the carboxyl functions. Since the carboxyl function will be easily formed by the oxidation of the aryl groups with ruthenium tetroxide, the temporary use of the aryl groups as a stable and non-reactive substitute for the carboxylic acid during the synthesis will be quite effective. -CO2H ) R u O~ Ar E C02H ( Ar Utilizing this methodology, we have succeeded in the efficient, convenient, and stereoselective synthesis of some natural products containing hydroxy amino acid functions (1-3), which are shown below. Mugineic acid (l), 3-epi-hydroxymugineic acid (2), 2'-hydroxynicotianamine (3), and distichonic acid A (4) are the phytosiderophores while polyoxamic acid (5) is the side chain moiety of the antifungal antibiotics polyoxins. Phytosiderophores The phytosiderophores produced in plants promote uptake and transport of iron required for the chlorophyll biosynthesis. Importance of the phytosiderophores in plant physiology as well as their unique amino acid structures have led us to synthesize them in an efficient manner suitable for the large scale production. In general, these phytosiderophores are composed of three parts, each of which is connected through the nitrogen atom. Thus, the three fragments should be synthesized first, and then the coupling of each fragment will follow to construct the whole molecule. 215