| The solution phase synthesis and analysis of small molecule library collections based on three scaffolds including dihydrodiazocinones, isoxazoles and indazolo-benzoxazines, has been developed. The condensation of 1,2,4,5-tetrazines with isoxazolylcyclobutanones in methanolic KOH provided conformationally restricted 6-isoxazole-5-yl-6,7dihydro-5H-[1,2]diazocin-4-ones. Conformational analysis, including 1H-NMR kinetic experiments, reveal two non-interconverting conformations of the eight-membered heterocycle with an activation energy of ∼21 kcal/mol. Theoretical calculations on model dihydrodiazocinones predict the conformational geometries of the two unique conformations while x-ray crystallographic analysis reveals the thermodynamic conformer. In addition to understanding the conformational analysis of the dihydrodiazocinones, x-ray crystallography was used for the analysis of 5-(3-bromobenzylcarbamoyl)-3-chloromethylisoxazole-4-carboxylate, the sole product of the selective nucleophilic chemistry associated with 3-chloromethylisoxazole-4,5-dicarboxylate. Treatment of 3-chloromethylisoxazole-4,5-dicarboxylate with various amines followed by thiolphenols provides a two-step synthesis to a 90-member library of drug-like isoxazoles. The third small molecule library was also based on two biologically active heterocycles. 2-(2-Nitro-benzylamino) benzyl alcohols participate in tandem intramolecular cyclization reactions in isopropanolic KOH to give indazolo[2,3,alpha][3,1]benzoxazines in good yields. A collection of indazolo-benzoxazines were synthesized to explore the steric and electronic limitations of the one-pot, two intramolecular cyclization reactions. Finally, to interface combinatorial libraries with biology, a novel selective aldose reductase assay has been developed to identify small molecule inhibitors. Simultaneously, an OBOC small molecule library was synthesized based on a triazine mass encoding strategy that accommodates cleavable linker, isotopic labeling, and diversity receptor moieties. The resulting triazine-based tags, enable the construction of a 1-oxa-2,8-diazaspiro[4.5]dec-2-ene-7-carboxamide library. Single bead analysis, facilitated by the similar ionization potential of the liberated tags led to the identification of compounds that selectively bind to aldose reductase. |
