12-Deoxyroridin J and 12-Deoxyepiisororidin E from Calcarisporium arbuscular. Issue 21 (23rd May 2018) - Matsumoto, Manami
Graphical abstract: Highlights: Novel roridin analogues possessing double bonds in place of the epoxide at C12. Configurational assignment at macrolide moiety by comparison with known analogues. ECD assignment at nearly vacuum UV region based on DFT calculations. Abstract: The culture broth of Calcarisporium arbuscular afforded 12-deoxyroridin J (1 ) and 12-deoxyepiisororidin E (2 ). Their structures were elucidated based on NMR and ECD analyses. Both molecules showed negative ECD splitting at 240 nm and a negative Cotton effect at 200 nm. Density functional theory calculations revealed that the former is caused due to the ECD exciton coupling between the C1′–C3′ enone and C7′–C11′ dienone chromophores, whereas the latter corresponds to the longer wavelength fragment of the negative ECD splitting in the vacuum ultraviolet (VUV) region at 190 nm which cannot be observed with conventional circular dichroism spectrometers. Simultaneous isolation of the regular roridins suggested that1 and2 are obtained through the same biosynthetic pathway. Since the 12-epoxy functionality is introduced at an early biosynthetic stage, 1 and2 are assumed to be derived from reductions of the 12, 13-epoxide in the corresponding regular roridins at a later biosynthetic stage.