Racemic S -

Dao et al.36 have shown that for racemic S(+)-2-aminobutane-gossy-polone-imine lowering temperature to 280 K has slowed the interconversion of the diastereomers. 

Th e have been few attempts to apply this method to the resolution of alcohols. Le Bel,6 following earlier experiments of Pasteur, failed to resolve racemic s-butyl carbinol by crystallization of the barium salt of the racemic hydrogen sulfate. di-Erythritol7 was found to be a racemic mixture, but the active crystals were too poorly forined to permit separation. It has been stated that dZ-cis-/3-decalol shows indications of being a resolvable racemic mixture, but no resolution has been described. 

Johnson disclosed the synthesis of the first reported allylic sulfoximine 104a in 1979 5 Treatment 0f racemic phenyl N-methylbenzenesulfonimidate 103 (X=OPh) with allyl lithium at 0-3 °C gave racemic S-allyl-/V-methyl-S-phenylsulfoximine 104a in 71% yield. Harmata75 has used a method related to that developed by Johnson6 to prepare the allylic sulfoximine 104b from the reaction of allyllithium with the sulfonimidoyl fluoride 103 (X=F). The yield, however, was low (20%). 

The aforementioned procedure was followed using a stable cell line of K562 cells expressing human a4(34. Testing results for experimental agent racemates, (S,S), and (.R,S) diastereomers are provided in Tables 2 1, respectively. 

Biological Measurement ( )- Propylisopropyl acetamide (R)- Propylisopropyl acetamide Racemate S/R... 

The efficiency of photoinduced racemization (S) of (R)-3b, due to recombination of 1-phenylethyEl-naphthyl radical pairs is given by Equation 13.14. ° In this equation, the conversion fraction is the part of 3b that has become photoproducts. The values of S, as calculated from the slopes of the plots in Fig. 13.3, are nearly constant, 0.13-0.16,... 

In order to extend the two-enzyme system to other 2-hydroxy acids, a racemase with a broader activity was found in Lactobacillus paracasei. This was exploited for deracemization of 2-hydroxy-4-phenylbutanoic acid and 3-phenyllactic acid, which are important synthetic intermediates. In addition, in this case the procedure requires a kinetic resolution step and a successive racemization step. O-Acetyl derivatives of the absolute (S)-configuration can be obtained in two successive repeating cycles. Yields are around 60%. Of course the 0-acetyl derivatives of opposite configuration can be obtained when the lipase-catalyzed reaction is apphed in the hydrolysis direction. Obtaining the O-acetyl derivatives of the absolute (R)-configuration requires an additional acetylation step of the initially resolved and racemized (S)-hydroxy acid [12]. 

When the /i-nitrostyrene 1 was treated with sodium methoxide, only the racemic (S, R )-diastereomer rac-2 was formed in 70% yield56. Clearly, basc-catalyzcd equilibration of the product may well account for this result. 

Figure 10. Transition state arrangements tor additions of non-racemic (S) a-oxygenated allylic stan-nanes to aldehydes.

Since attachment of a methyl group at the alpha position of 5 (Table II) Improved activity substantially, several racemic S - oC-(methyl)benzyl thiolcarbamates and dlthiocarbamates were synthesized and assessed for activity. Data In Table IV show that, except for 41 and 47, o<-(methyl)benzyl analogs were more effective than thelr benzyl counterparts. Data also show that < -methyl substituted thiolcarbamates were consistently more effective than their corresponding dlthiocarbamates. The chiral center In -(methyl-benzyl analogs poses a question regarding Its Influence on activity. Since only racemic samples were evaluated In this study, future studies should Include evaluation of appropriate enantiomers. 

Note all racemic /S-blockers were resolved. The S-timolol values are for k R, k s and separation factor, 2, in parentheses. 

HPMC matrix tablets, a greater enantioselectivity was observed with a physical mixture of enantiomers (K2) compared to formulations made with racemate (Kl). While from both formulations the S enantiomer was released faster than the R enantiomer, the S/R ratio was significantly higher (S/R ratio >5) in the case of the physical mixture compared to formulations made with racemate (S/R ratio 1.5) (Fig. 11). When the release of enantiomers of ketoprofen presented as physical mixtures was compared from HPMC (K2) and Eudragit RL (K5), matrices, only the chiral HPMC matrix has shown stereoselectivity with the S/R ratios ranging between... 

S. occurs as the (-)-form (hyoscine) in several Solan-aceae genera [e. g. Atropa belladonna (deadly nightshade), Datura species (thorn apple), Duboisia species, Hyoscyamus species (henbane), Mandragora officinalis (mandrake), and Scopolia species (banewort)]. Racemic S. (atroscine) is a natural product of the Solanaceae Datura innoxia, Hyoscyamus niger, and Scopolia camiolica. S. is easily hydrolyzed in acidic and alkaline solution to tropic acid and scopine. 

Racemates s. Stereoisomers Racemization s. under Radical reactions Radical reactions... 

Figure 8.17 Schematic representation of a racemic S-sheet architecture composed of isotactic (R)- and (S)- oiigopep-tide chains, showing the enantioseiective reaction with a (R)-NCA-monomer moiecuie oniy at the ieft-side rim.

N-carbobenzoxy-DL-alanine (Y 88%) and DL-trans-5-methyl-2-oxazolidone-4-carboxylic acid (Y 91%). F. e., also with optically active compounds without racemization, s. T. Kaneko and T. Inui, Bull. Ghem. Soc. Japan 36, 1541 (1963). 

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