RESUMO
Full details are provided for the total synthesis of several members of the hapalindole family of natural products, including hapalindole Q, 12-epi-hapalindole D, 12-epi-fischerindole U, 12-epi-fischerindole G, 12-epi-fischerindole I, and welwitindolinone A. Use of the recently developed direct indole coupling enabled an efficient, practical, scalable, and protecting-group-free synthesis of each of these natural products. The original biosynthetic proposal is reviewed, and a revised biosynthetic hypothesis is suggested, validated by the above syntheses. The syntheses are also characterized by an adherence to the concept of "redox economy". Analogous to "atom economy" or "step economy", "redox economy" minimizes the superfluous redox manipulations within a synthesis; rather, the oxidation state of intermediates linearly and steadily increases throughout the course of the synthesis.
Assuntos
Alcaloides/síntese química , Indóis/síntese química , Alcaloides/biossíntese , Materiais Biomiméticos/química , Alcaloides Indólicos , Nitrilas/síntese química , Oxirredução , EstereoisomerismoRESUMO
Full details are provided for a recently invented method to couple indoles and pyrroles to carbonyl compounds. The reaction is ideally suited for structurally complex substrates and exhibits high levels of chemoselectivity (functional group tolerability), regioselectivity (coupling occurs exclusively at C-3 of indole or C-2 of pyrrole), stereoselectivity (substrate control), and practicality (amenable to scaleup). In addition, quaternary stereocenters are easily and predictably generated. The reaction has been applied to a number of synthetic problems including total syntheses of members of the hapalindole family of natural products, ketorolac, acremoauxin A, and oxazinin 3. Mechanistically, this coupling protocol appears to operate by a single electron-transfer process requiring generation of an electron-deficient radical adjacent to a carbonyl which is then intercepted by an indole or pyrrole anion.
