Procedure-Economical, Enantioselective Total Syntheses of Polycyclic Natural Products and Analogues Containing a 3a-Hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic Acid Residue

Abstract

The 3a-hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic acid (HPIC) residue and its aza-analogue are found in many bioactive natural products. In this account, short divergent total syntheses of several such natural products, diastereomers and analogues are described. It is demonstrated that by appropriate combination of different efficient tactics such as biomimetic/bio-inspired synthesis, chemo/regioselective reactions, umpolung of regioselectivity and/or reactivity, and tandem reactions, the enantioselective syntheses of polycyclic molecules such as (+)-asperlicin E and (–)-robustanoids A and B can be achieved in a protecting-group-free and redox-economical manner, in only three to four steps starting from l-tryptophan.1 Introduction2 Strategic Considerations2.1 Occurrence of HO-HPIC and HO-aza-HPIC Residues in Natural Products2.2 Biosyntheses of HO-HPIC and HO-aza-HPIC Residues2.3 Chemical Syntheses of HO-HPIC and HO-aza-HPIC Residues3 Procedure-Economical Syntheses of HO-HPIC-Containing Natural Products3.1 Protecting-Group-Free Syntheses of Asperlicin E, Its Diastereomer, and an Analogue3.2 Divergent Syntheses of (–)-Robustanoids A and B, a Diastereomer, and Analogues4 Conclusion and Future Perspectives