New sesquiterpenoid isonitriles from three species of phyllidid nudibranchs.

Chemical investigation of the two nudibranch species Phyllidiella pustulosa and Phyllidia ocellata collected in Queensland, Australia, provided new stereoisomers of 4-isocyano-9-amorphene (1) and of 10-isocyano-4-amorphene (2), respectively. A specimen of Phyllidia picta collected from Bali, Indonesia, contained the axane sesquiterpenoids pictaisonitrile-1 (3) and pictaisonitrile-2 (4). The planar structures were elucidated using 1D and 2D NMR spectroscopy, while relative configurations were established using NOESY correlations, coupling constant data, and comparison with literature data.

Catalyst-Controlled Stereoselective Synthesis Secures the Structure of the Antimalarial Isocyanoterpene Pustulosaisonitrile-1.

Three new isocyanoditerpenes (5-7) have been characterized from Australian specimens of the nudibranch Phyllidiella pustulosa. The planar structure and (3R,6S,7R) absolute configuration of pustulosaisonitrile-1 were deduced by spectroscopic analyses at 900 MHz informed by molecular modeling, DFT calculations, and computational NMR chemical shift predictions and by comparison of experimental electronic circular dichroism (ECD) data with TDDFT-ECD calculations for the truncated model compound 8. A catalyst-controlled enantio- and diastereoselective total synthesis of the two most likely diastereomeric candidates for the structure of 5 solidified its (3R,6S,7R,10S,11R,14R) absolute configuration. Three individual enantioselective methods provided stereochemical control at key positions, permitting an unambiguous final structural assignment. Isocyanide 5 and synthetic diastereomers 5a and 5c showed activity against Plasmodium falciparum malaria parasites (IC50 ∼1 µM).