Directed Self-Assembly with Gallic Acid Provides First Phenolic Acid Cocrystals for the Antiviral Drug Acyclovir toward Increasing Pharmaceutical Features and Synergy: A Theoretical and Experimental Integration Research

To achieve new breakthroughs in the development of synergistic antiviral medication cocrystals of acyclovir (AYL) with phenolic acids, a cocrystallization-driven strategy for optimizing the physicochemical properties and increasing the antiviral efficacy is proposed. This method emphasizes the structural features and medicinal value together with the dominant properties of gallic acid (GLA) to promote both solubility and permeability of AYL by cocrystallizing GLA into AYL's lattice; meanwhile, the antiviral ability of ALY can be greatly increased by activating the antiviral potential of GLA and utilizing the synergistic antiviral activity of both in cocrystal formation. Guided by this idea, the first AYL-phenolic acid cocrystal, AYL-GLA-2H2O, is orientationally constructed and fully characterized. The accurate cocrystal structure revealed by single-crystal X-ray diffraction indicates that the entry of GLA into the AYL lattice has disrupted the homodimer of AYL itself, leading to the formation of a hydrophobic heterodimer between AYL and GLA molecules, coupled with an aqueous tetramer, thus endowing the cocrystal with both hydrophilic and hydrophobic characteristics. Such structural feature induces a concurrent enhancement in dissolubility and permeability of the cocrystal compared with the parent medicine. These observations can be strongly supported by density functional theory-based theoretical investigations involving molecular electrostatic potential, Hirshfeld surface, frontier molecular orbital, and Gibbs solvation free energy. Interestingly, the perfected AYL's properties along with the stimulated antiviral activity of GLA enable the two ingredients in the cocrystal to display synergistic antiviral activity against the herpes simplex virus with a cooperativity index of less than 1, contributing to enhancing the antiviral ability. Thus, this contribution not only highlights the effectiveness of combining theory with experiment to solve AYL's issues via the cocrystallization-driven method but fills in the gaps from previous studies on AYL-phenolic acid cocrystals with synergistic antiviral effects.