Novel asymmetric total syntheses of (R)-(-)-pyridindolol, (R)-(-)-pyridindolol K1, and (R)-(-)-pyridindolol K2 via a mild one-pot aromatization of N-tosyl-tetrahydro-β-carboline with (S)-2,3-O-isopropylidene-L-glyceraldehyde as the source of chirality

Novel total syntheses of (R)-(-)-pyridindolol 1, (R)-(-)-pyridindolol K1 2, and (R)-(-)-pyridindolol K2 3 are described. By using L-tryptophan methyl ester and (S)-2,3-O-isopropylidene-L-glyceraldehyde as the starting materials, (R)-(-)-pyridindolol 1, (R)-(-)-pyridindolol K1 2, and (R)-(-)-pyridindolol K2 3 were synthesized in 5-7 steps in 66%, 41%, and 55% overall yields, respectively. The characteristic step of the total syntheses is a mild one-pot aromatization of N-tosyl-1,2,3,4-tetrahydro-beta-carboline (N-Ts-THBC), which was obtained via Pictet-Spengler reaction of L-tryptophan methyl ester with (S)-2,3-O-isopropylidene-L-glyceraldehyde, and subsequent N-tosylation. (C) 2013 Elsevier Ltd. All rights reserved.