RS-8359, (+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine is a selective and reversible MAO-A inhibitor. The (S)-enantiomer of RS-8359 has been demonstrated to be inverted to the (R)-enantiomer after oral administration to rats. In the current study, we investigated the chiral inversion mechanism and the properties of involved enzymes using rat liver subcellular fractions. The 7-hydroxy function of RS-8359 was oxidized at least by the two different enzymes. The cytosolic enzyme oxidized enantiospecifically the (S)-enantiomer with NADP as a cofactor. On the other hand, the microsomal enzyme catalyzed more preferentially the oxidation of the (S)-enantiomer than the (R)-enantiomer with NAD as a cofactor. With to product enantioselectivity of reduction of the 7-keto derivative, it was found that only the alcohol bearing (R)-configuration was formed by the cytosolic enzyme with NADPH and the microsomal enzyme with NADH at almost equal rate. The reduction rate was much larger than the oxidation rate of 7-hydroxy group. The results suggest that the chiral inversion might occur via an enantioselectivity of consecutive two opposing reactions, oxidation and reduction of keto-alcohol group. In this case, the direction of chiral inversion from the (S)-enantiomer to the (R)-enantiomer is governed by the enantiospecific reduction of intermediate 7-keto group to the alcohol with (R)-configuration. The enzyme responsible for the enantiospecific reduction of the 7-keto group was purified from rat liver cytosolic fractions and identified as 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) via database search of peptide mass data obtained by nano-LC/MS/MS.

The A–X transition of diatomic bismuth, Bi2, was revisited by laser induced fluorescence in solid Ne at 3 K. Molecular constants, i.e., vibrational frequencies of 137 cm–1 and 174 cm–1, were reproduced for the upper and lower electronic states as reported by Bondybey et al. [Chem. Phys. Lett. 76, 30 (1980)]. Two-dimensional mapping of emission spectra confirmed satellite bands in higher and lower excitation/emission energies for each of the major bands in the vibrational progression of v′–v″ (v′ = 0–5, v″ = 5–12). Based on the molecular orbital calculations, presence of clusters, Bi2Nen (n = 1–6), is proposed for possible carriers of the observed satellites. For the relatively large matrix shift of ∼67 cm−1 in solid Ne for the term energy of the A state, the diatomic bismuth is supposed to exist as a linearly coordinated cluster of Bi2Ne in the matrix.