The hydrophobic dl-amino acids alanine, valine, leucine, and isoleucine have been cocrystallized with LiCl via solid-state and solution methods, and the effect of preparation conditions and solvent choice on the racemic versus conglomerate formation has been investigated. For the sake of comparison, enantiopure l-amino acids have also been reacted with LiCl in the same experimental conditions. With dl-alanine only, a racemic ionic cocrystal of formula dl-alanine·LiCl·H2O is obtained, irrespective of the preparation conditions, while the amino acids dl-valine and dl-leucine undergo spontaneous chiral resolution when MeOH is used in ball milling conditions, yielding monohydrated conglomerates, which at ambient conditions convert over time into the racemic ionic cocrystals dl-Val·LiCl·H2O and dl-Leu·LiCl·1.5H2O; these racemic ionic cocrystals (ICCs) are otherwise obtained in a single step if water is employed instead of MeOH, both in ball milling and solution conditions. dl-Isoleucine behaves differently, and product characterization is complicated by the presence of dl-alloisoleucine (dl-aIle) in the commercial starting material; solution crystallization in the presence of excess LiCl, however, unexpectedly results in the formation of the alloisoleucine conglomerate d-aIle·LiCl·H2O and l-aIle·LiCl·H2O, together with unreacted dl-isoleucine. Solid-state syntheses of the ionic cocrystals proceed in most cases via formation of intermediate metastable polymorphs; phase identification and structural characterization for all ICCs have been conducted via single crystal and/or powder X-ray diffraction.

Shemchuk O., Spoletti E., Braga D., Grepioni F. (2021). Solvent Effect on the Preparation of Ionic Cocrystals of dl -Amino Acids with Lithium Chloride: Conglomerate versus Racemate Formation. CRYSTAL GROWTH & DESIGN, 21(6), 3438-3448 [10.1021/acs.cgd.1c00216].

Solvent Effect on the Preparation of Ionic Cocrystals of dl -Amino Acids with Lithium Chloride: Conglomerate versus Racemate Formation

Shemchuk O.;Braga D.;Grepioni F.
2021

Abstract

The hydrophobic dl-amino acids alanine, valine, leucine, and isoleucine have been cocrystallized with LiCl via solid-state and solution methods, and the effect of preparation conditions and solvent choice on the racemic versus conglomerate formation has been investigated. For the sake of comparison, enantiopure l-amino acids have also been reacted with LiCl in the same experimental conditions. With dl-alanine only, a racemic ionic cocrystal of formula dl-alanine·LiCl·H2O is obtained, irrespective of the preparation conditions, while the amino acids dl-valine and dl-leucine undergo spontaneous chiral resolution when MeOH is used in ball milling conditions, yielding monohydrated conglomerates, which at ambient conditions convert over time into the racemic ionic cocrystals dl-Val·LiCl·H2O and dl-Leu·LiCl·1.5H2O; these racemic ionic cocrystals (ICCs) are otherwise obtained in a single step if water is employed instead of MeOH, both in ball milling and solution conditions. dl-Isoleucine behaves differently, and product characterization is complicated by the presence of dl-alloisoleucine (dl-aIle) in the commercial starting material; solution crystallization in the presence of excess LiCl, however, unexpectedly results in the formation of the alloisoleucine conglomerate d-aIle·LiCl·H2O and l-aIle·LiCl·H2O, together with unreacted dl-isoleucine. Solid-state syntheses of the ionic cocrystals proceed in most cases via formation of intermediate metastable polymorphs; phase identification and structural characterization for all ICCs have been conducted via single crystal and/or powder X-ray diffraction.
2021
Shemchuk O., Spoletti E., Braga D., Grepioni F. (2021). Solvent Effect on the Preparation of Ionic Cocrystals of dl -Amino Acids with Lithium Chloride: Conglomerate versus Racemate Formation. CRYSTAL GROWTH & DESIGN, 21(6), 3438-3448 [10.1021/acs.cgd.1c00216].
Shemchuk O.; Spoletti E.; Braga D.; Grepioni F.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/855299
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