Enantioselective syntheses of syributin 1 and novel C-glycosidic elicitors syringolides 1 and 2

Concise enantioselective syntheses of syributin 1 (3) and the novel nonproteinaceous C-glycosidic elicitors syringolides 1 and 2 (1 and 2, respectively), isolated from Pseudomonas syringae pv. tomato, are described. Syributin 1 was synthesized in one step by the Sharpless catalytic asymmetric dihydroxylation (AD reaction) of (1'E)-3-(3'-(octanoyloxy)-1'-propenyl)but-2-en-4-olide (13) in 72% yield with >98% ee. Furthermore, alkylation of (1'R,2'R)-3-[1'-(tert-butyldimethylsiloxy)-2,3'- (isopropylidenedioxy)propyl]but-2-en-4-olide (20), prepared from (1'E)-3-[3'-(tert-butyldimethylsiloxy)-1'-propenyl]but-2-en-4-olide (11) by the AD reaction, with hexanal or octanal by Jefford's procedure at the a position to the lactone carbonyl group gave adduct 21 or 22 in good yield. Oxidation of 21 or 2;2, followed by removal of the protecting groups, provided syringolide 1 or 2, respectively.