Total Synthesis of Marine Natural Products (+)-Strongylin A and Corallidictyal D by Regio- and Stereoselective Cyclization of Alkenyl Benzenes

Total Syntheses of Avapyran and Dysiquinol D through a Stereoconvergent Fusion of Dihydrobenzopyran

Asymmetric total syntheses of avapyran, dysiquinol D, and 8-epi-dysiquinol D are reported. The key steps involved in the syntheses are selective formation of an all-carbon quaternary stereocenter under Birch conditions, an unprecedented acid-mediated stereoconvergent installation of a cis-dihydrobenzopyran unit, and the reagent-controlled regioselective dehydration of tertiary alcohol.

Stereoselective Synthesis of Xylodonin A and 22-Hydroxyxylodonin A and Discovery of Analogues with Cytotoxic Activity

The first and stereoselective synthesis of xylodonin A and 22-hydroxyxylodonin A, two drimane-type sesquiterpenoid natural products, was developed from the readily available (+)-sclareolide. This route features an allylic oxidation and acid-promoted dehydration for construction of the key intermediate 6-hydroxyisodrimenin. Representative analogues were synthesized, and their previously unknown bioactivities were revealed after biological evaluation. The analogue 19a exhibited cytotoxic activity against liver cancer HepG2 cells (IC50: 8.8 vs 5.9 μM) that was comparable to that of the clinical anticancer drug etoposide with lower toxicity to normal liver HL7702 cells (IC50 > 100 μM).

Divergent and Stereoselective Synthesis of Ustusal A, (-)-Albrassitriol, and Elegansin D

The first synthesis of ustusal A as well as expeditious access to (-)-albrassitriol is described as featuring a singlet oxygen [4 + 2] cycloaddition, achieving the desired stereoselectivity for the 1,4-cis-hydroxyl groups. Transformation of (+)-sclareolide to III followed by a key Horner-Wadsworth-Emmons (HWE) reaction and stereospecific allylic oxidation facilitated the first synthesis of elegansin D. The biological evaluation of these natural products together with seven elegansin D analogues was performed, among which several elegansin D analogues exhibited potential anticancer activity against liver cancer HepG2 cells (IC50 = 11.99-25.58 μM) with low cytotoxicity on normal liver HL7702 cells (IC50 > 100 μM).