Transformations of Quinic Acid. Asymmetric Synthesis and Absolute Configuration of Mycosporin I and Mycosporin-gly
作者:James D. White、Janice H. Cammack、Kazuhiko Sakuma、Gordon W. Rewcastle、Rexford K. Widener
DOI:10.1021/jo00117a008
日期:1995.6
D-(-)-Quinic acid (1) was converted to the fungal metabolites mycosporin I (2) and mycosporin-gly (13) via the iminophosphorane 64. The latter was prepared in 10 steps from 1 using oxidative bromination of quinide 33 to furnish 41. Reduction of the gamma-lactone, followed by protection of the 1,2-diol, was accompanied by migration of the benzoyl group to yield 43. The latter was oxidized to 47 which underwent displacement by sulfinate to give 59. O-Methylation, followed by reduction of the benzoate, afforded 61. Oxidation of 61 produced 62 which was converted to beta-azido enone 63. Treatment of 63 with triphenylphosphine gave crystalline 64. An aza-Wittig reaction of 64 with glyoxylate and reduction of the resultant imine yielded 68 which, after deprotection, afforded 13. Analogous coupling of 64 with diethyl ketomalonate and subsequent reduction of the ester groups led to 2. Mycosporin I and mycosporin-gly are shown by this sequence to possess S absolute configuration.