A DFT investigation of structure and spectroscopic properties of haplophytine and its half-molecules

The natural product haplophytine and its half-molecules, aspidophytine and the still elusive ‘left domain’, exhibit unique structural skeletons and unusual spectroscopic features. These issues have been tackled with density functional calculations. The congested framework of haplophytine consists of two heteropolycyclic segments connected with a sterically demanding single bond and incorporates two protonation sites of different basicity and a relatively strong hydrogen bond O–H⋯O, responsible for the acidic activity. The molecular and electronic structure of these alkaloids has been elucidated by analysing the carbonyl vibrations, 13C NMR chemical shifts, and UV absorption spectra that are most sensitive to stereoelectronic factors.