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The preparation of (3-hydroxy-a-amino acids from glycine and various aldehydes by-aldolase enzymes is examined; attention is focused on substrate structural requirements, with stereoselectivity of the aldol reactions also considered.

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A general procedure for the conversion of a-oximido-8-keto esters into vicinal tricarbonyl moieties by TiCla in aqueous, buffered (PH 5) conditions with acetone cowlvent waa demonstrated. As applied to N-hydroxy 8-lactam 17, which contained an a-oximido-&keto ester side chain, these combined reductive and hydrolytic conditions effected simultaneous tricarbonyl formation and @-lactam N-O bond reduction. Vicinal tricarbonyl-containing N-unsubstituted &lactam 18 was a direct precursor to semifunctionalized carbacephem 1.The demonstrated synthetic utility of the 1,2,3-tricarbonyl functionality by Wasserman is mainly responsible for the current interest in this important moiety. Several classes of biologically active alkaloids have been synthesized by routes employing it as part of key intermediates.' Furthermore, the functionality has been found in nature-the immunomodulating agent FK-5062 and related antibiotics3 contain a latent vicinal tricarbonyl group.Several syntheses of the vicinal tricarbonyl moiety have been published: many of which use a 8-keto ester as the startingThese methods include conversion of the &keto ester into an a-enamino-or a-(phenyl-iodoniumy1)-@-keto ester followed by oxidative cleavage by singlet oxygen5 or ozonolysis,6 respectively. Formation of an a-imino-&keto ester with subsequent hydr01ysis'~J~' or synthesis of a &keto-a-nosy1 ester followed by reaction with base led to the vicinal tricarbonyl moiety.8 (10) (a) Zmijewski, M. J.; Briggs, B. S.; Thompson, A. R.; Wright, I. G. Tetrahedron Lett. 1991,32, 1621. (b) Bodurow, C.; C. Boyer, B. D.; Brennan, J.; Bunnell, C. A.; Burks, J. E.; Carr, M. A.; Doecke, C. W.; Eckrich, T. M.; Fisher, J. W.; Gardner, J. P.; Graves, B. J.; Hines, P.; Hoying, R. C.; Jackson, B. G.; Kinnick, M. D.; Kochert, C. D.; Lewis, J. S.; Luke, W. D.; Moore, L. L.; Morin, Jr., J. M.; Nist, R. L.; Prather, D. Abstract no. 1187. (d) Gray, G.; Ramotar, K.; Krulicki, W.; Louie, T. J. Ibid. Abstract no. 1200. (e) Quay, J. F.; Coleman, D. L.; Finch, L. S.; Indelicap, J. M.; Pasini, C. E.; Shoufler, J. R.; Sullivan, H. R.; Turner, J. C. Zbtd. Abstract no. 1205. (11) (a) Guthikonda, R. N.; Came, L. D.; Christensen, B. G. J. Am. Chem. SOC. 1974,96,7584. (b) Hatanaka, M.; Ishimam, T. Tetrahedron Lett. 1983,24, 4837. (c) Mochida, K.; Hirata, T. Chem. Pharm. Bull. 1988,36, 3642.

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