Abstract
We report a procedure—economical method for the highly enantioselective and protecting-group free total syntheses of nonpeptidal CCK antagonists asperlicins C and E. Starting from l-tryptophan, the synthesis of asperlicin C has been achieved in three steps, which features the low-valent titanium (LVT: TiCl4–Zn combination)-mediated reductive cyclization of o-nitrobenzamide to construct the (3H)-quinazolin-4-one moiety. This is the first employment of LVT for the synthesis of asperlicin C, which allowed accessing asperlicin C in >99% enantioselectivity. Asperlicin C was converted, in one-pot, into asperlicin E and 2,3-di-epi-asperlicin E by dimethyl dioxirane (DMDO)-mediated tandem reactions. The use of DMDO as a green, cheap, and easily available oxidant to replace the photochemical method renders the synthesis of asperlicin E experimentally convenient.
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