Rumiko Sakurai

Resolution of 3-(methylamino)-1-(2-thienyl)propan-1-ol, a new key intermediate for duloxetine, with (S)-mandelic acid

Abstract The resolution of racemic 3-(methylamino)-1-(2-thienyl)propan-1-ol 3, a new key intermediate for duloxetine 1, was studied. The conditions were optimized for an industrial-scale resolution of 3 by using (S)-mandelic acid 4 as a resolving agent and 2-butanol containing 2 equimolar amounts of water as a solvent. The (S)-3·(S)-4·H2O diastereomeric salt was crystallized to give pure (S)-3 with >99.9% e.e. after liberation of the amine. The absolute configuration of liberated (−)-3 was determined as (S) by X-ray crystallography.

Molecular mechanism of dielectrically controlled optical resolution (DCR)

We have recently found the first example of dielectrically controlled optical resolution (DCR). By adjusting the dielectric constant of the solvent used in the resolution process, each optical isomer of (R,S)-alpha-amino-epsilon-caprolactam can be selectively obtained using N-tosyl-(S)-phenylalanine as a chiral selector. The molecular mechanism of DCR has been investigated by comparing the molecular and crystal structures of the optical selector, its target substrate and their diastereomeric salts. Strong hydrophobic interactions between the phenyl rings of the optical selector govern the molecular aggregation of the selectors and form a hydrophilic layer in which molecular recognition takes place. The recognition site in the hydrophilic layer can inherently identify both of the isomers. The dielectric constant of the solvent used in the discrimination process controls the intermolecular interaction which determines the isomer to be selected. The molecular mechanism of DCR disclosed in this study strongly suggests that DCR is not a specific but a general phenomenon. This method can be applicable to a large variety of optical resolution processes.

Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine via diastereomeric salt formation.

Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine 1 by N-(p-toluenesulfonyl)-(S)-phenylalanine 2 via diastereomeric salt formation was studied. (S)-1·(S)-2 was preferentially crystallized as a less-soluble salt from aqueous alcohol, while (R)-1·(S)-2 salt was mainly obtained by addition of solvents with a six-membered ring such as dioxane, cyclohexane, tetrahydropyran, and cyclohexene to 2-propanol. Further investigations were carried out from the viewpoints of molecular structures, optical rotation measurement, and X-ray crystallographic analyses. Crystallographic analyses have revealed that incorporation of the six-membered ring solvent molecule in (R)-1·(S)-2 without hydrogen bonds changed the molecular conformation of (S)-2 to stabilize the salt, which changed the selectivity of 1 in the enantioseparation.

Resolution of racemic cis-1-amino-2-indanol by diastereomeric salt formation with (S)-2-phenylpropionic acid

Abstract Resolution of racemic cis -1-amino-2-indanol 1 , a key intermediate for the synthesis of indinavir, is reported. The conditions were optimized for an industrial-scale resolution of racemic cis - 1 using ( S )-2-phenylpropionic acid 6 as the resolving agent and ethanol as the solvent. The less-soluble diastereomeric salt, (1 R ,2 S )- 1 ·( S )- 6 , was obtained in 35% yield with 99% de ( E >69%) by crystallization. Resolving agent 6 was efficiently recovered from the salt and the mother liquor.