Comparison of the Molecular Properties of Euglobals Differing by the Mutual Positions of the Two R–C=O Groups (R = H and CH2CH(CH3)2): A Computational Study

Euglobals are a subclass of acylphloroglucinols, mostly found in plants of the Eucalyptus genus. They possess anticancer activity, being potent inhibitors of the Epstein–Barr virus activation. Their molecules can be viewed as acylphloroglucinol monoterpene or sesquiterpene adducts, with the former having greater activity than the latter. The acylphloroglucinol moiety contains two mutually meta acyl (R–C=O) groups, respectively, in ortho and meta positions with respect to the two C atoms shared by the two moieties. The current work focuses on euglobal molecules in which R = H is in one acyl group and R = isobutyl is in the other. It aims to identify the property differences between molecules having the same terpene moiety and the two acyl groups in reversed positions. Ten such pairs were studied computationally using different levels of theory (HF, DFT, and MP2). The results highlight considerable differences between the two molecules of each pair, regarding molecular features such as relative energies, characteristics of the intramolecular hydrogen bonds (IHBs), dipole moment, bond vibrational frequencies, and frequency changes caused by the IHBs. A comparison of the results from the different levels of theory utilised shows similar patterns for the influence of position reversal on the same characteristic.