Studies on molecular properties prediction and histamine H3 receptor affinities of novel ligands with uracil-based motifs

Unexpected Reaction Products of Uracil and Its Methyl Derivatives with Acetic Anhydride and Methylene Chloride

New acetyl derivatives of uracil, 6-methyluracil, and thymine were obtained in the course of an unconventional synthesis in methylene chloride. It was shown that products with the acetyloxymethyl fragment are formed according to a mechanism different from that for products with the acetyloxyethyl group. In particular, for uracil it was proven that the reaction with Ac₂O, TEA, and CH₂Cl₂ leads to 1-acetyloxymethyluracil, where the N¹ substituent is composed of the -CH₂- fragment that originated from CH₂Cl₂ and the 1-acetyloxy moiety from Ac₂O. The reaction of uracil with Ac₂O, TEA, CH₂Cl₂, and DMAP leads to an acetyloxyethyl derivative in which the -CH₂-CH₂- fragment originates from TEA and the 1-acetyloxy moiety from Ac₂O. A possible mechanism for the formation of new compounds was suggested and supported by the density functional theory/B3LYP quantum mechanical calculations. New compounds (39 in total, including seven deuterated) were fully characterized by nuclear magnetic resonance and high-resolution mass spectrometry techniques.

A diversity of alkylation/acylation products of uracil and its derivatives: synthesis and a structural study

tert-Butyl dicarbonate (Boc2O) and ethyl iodide (EtI) reactions with uracil (U), thymine (T) and 6-methyluracil (6-MU) were performed following routine procedures in pyridine/DMF solvents and with DMAP as the catalyst. Among 20 synthesized compounds, a derivative of 6-methyluracil substituted by the Boc-pyridine moiety at the C5 position appeared unexpectedly. The NMR spectra confirmed the molecular structure of all uracil derivatives. Parallel quantum mechanical DFT calculations supported the experimental findings.

Cherry-picked ligands at histamine receptor subtypes

Histamine, a biogenic amine, is considered as a principle mediator of multiple physiological effects through binding to its H1, H2, H3, and H4 receptors (H1-H4Rs). Currently, the HRs have gained attention as important targets for the treatment of several diseases and disorders ranging from allergy to Alzheimer's disease and immune deficiency. Accordingly, medicinal chemistry studies exploring histamine-like molecules and their physicochemical properties by binding and interacting with the four HRs has led to the development of a diversity of agonists and antagonists that display selectivity for each HR subtype. An overview on H1-R4Rs and developed ligands representing some key steps in development is provided here combined with a short description of structure-activity relationships for each class. Main chemical diversities, pharmacophores, and pharmacological profiles of most innovative H1-H4R agonists and antagonists are highlighted. Therefore, this overview should support the rational choice for the optimal ligand selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies. This article is part of the Special Issue entitled 'Histamine Receptors'.