Enantioselective synthesis for the antipodes of slagenins B and C: establishment of absolute stereochemistry.

[reaction: see text] The total synthesis for the (-)-antipode of slagenin B (12) and the (+)-antipode of slagenin C (13) was achieved with the condensation of glyoxal hydrate 10 and urea as the key step. The absolute stereochemistries of naturally isolated slagenins B and C were assigned to be (9R,11R,15R)-1b and (9R,11S,15S)-1c, respectively.