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QSAR of Radical Inactivation by Selected Anthraquinones

Anthraquinones are natural antioxidants capable to combat the progression of various diseases [1]. Among underlying health promoting mechanisms, radical scavenging could be operative via several possible processes [2]. In building QSAR models, among thousands molecular descriptors we preferred those with clear physicochemical meaning related to antiradical mechanisms, e.g., bond dissociation enthalpy (BDE) as a general parameter for (poly)phenolics radical scavenging activity, 13C NMR chemical shift of C atom adjacent to phenolic OH group [3], aromaticity indices (e.g. ring current index, RCI [4]), hydrogen bonding indices, etc. Due to limited number of compounds (12 anthraquinones [5]), only models with one or two descriptors are acceptable. The best one descriptor model, using 13C NMRmin chemical shift (r = −0.983, rcv = −0.969), is presented in Fig. 1. The phenolic OH group with more abstractable H atom shielded the 13C nucleus from the external magnetic field more effectively than the OH group with less abstractable H atom. One descriptor models using BDE and RCI, are slightly inferior: r = −0.934 (rcv = −0.904) and r = 0.914 (rcv = −0.848), respectively. The best two descriptor model embraces 13C NMRmin chemical shift and RDF055m descriptor (related to the 3D positions of the atoms) and possesses only slightly better statistics: r = −0.990, rcv = −0.979. It should be emphasized that obtained model(s) are transferable to flavones [6], another class of (poly)phenols, Fig 2.

QSAR ; anthraquinones ; BDE ; RCI ; 13C NMR

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