Total Synthesis of Leptochartamides A and B: Two Enantiomeric Pairs of Hydroxybenzyl Dimers from a Deep-Sea Fungus Leptosphaerulina chartarum .

Leptochartamides A and B (± 1 and ± 2 ), two pairs of enantiomeric hybrids with the same cyclo-bridged skeleton containing an unusual dioxa-azabicyclo[3.2.1]octane core system, were isolated from the deep-sea-derived fungus Leptosphaerulina chartarum . Their structures were determined by detailed spectroscopic analysis, single-crystal X-ray diffraction, electronic circular dichroism calculations, and the total synthesis. Compounds 2a and 2b showed selective cytotoxicity against Ewings sarcoma cells A673, with IC 50 values of 8.98 ± 0.23 and 4.18 ± 0.27 μM, respectively. The colony formation assay of compounds 2a and 2b against A673 cells was completed.