Dual Space Divergence in Small Molecule Quasiracemates: Benzoyl Valine and Norvaline Assemblies

Abstract

The structural boundary governing small molecule quasiracemate formation is determined by both the molecular framework and the nature of the structural modifications introduced into the quasienantiomeric components. To investigate this boundary, we assembled D-N-(4-CF3-benzoyl) valine (D-1-CF3) with a homologous series of L-benzoyl norvaline (L-2-X) quasienantiomers. Because the norvaline derivatives in this study differ systematically through iterative substitution of X (from H to Ph), this series provides an ideal platform for probing the limits of molecular recognition based on complementary molecular shapes. Examining systems with two points of structural variation affords a detailed view of the quasiracemate landscape. Crystallographic analyses of these quasiracemates and their corresponding racemic counterparts (21 samples in total) reveal two distinct hydrogen bond motifs, governed by the spatial characteristics of the molecular components. These non-bonded interactions stabilize crystal lattices that accommodate cocrystallization across nearly the entire series. The only exceptions are (±)-2-Ph and D-1-CF3/L-2-Ph, which fail to cocrystallize and therefore define the structural boundary of molecular recognition within the system. In addition, this study describes a diagnostic tool to quantitatively evaluate the relationship among quasiracemate formation, molecular shape complementarity, and the degree of near inversion symmetry between the quasienantiomeric components.