2-methyl-1,2-diols resolution

The importance of proper immobilization of enzymes can be shown in the kinetic resolution of racemic a-acetoxyamides. This group of compounds is an important class of chemicals since they can be readily transformed into a-amino acids [17], N-methylated amino acids, and tripeptide mimetics [18], amino alcohols [19], 1,2-diols [20], 1,2-diamines [21], and enantiopure l,4-dihydro-4-phenyl isoquinolinones [22]. 

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

Enantiopure 2,2,5,5-tetramethyl-3,4-hexanediol was prepared by Yamanoi and Imamoto [46]. A combination of Ti(0-i-Pr)4 with this diol (1 2) gives a chiral catalyst for sulfide oxidation with cumyl hydroperoxide in the presence of 4A molecular sieves in toluene. At -20°C p-tolyl methyl sulfoxide (95% ee) was obtained in 42% yield together with 40% sulfone, A kinetic resolution increased, to some extent, the enantiomeric excess of the product, that is, at lower conversion (20% yield) the enantiopurity of the resulting sulfoxide was only 40% ee. This catalytic system is ineffective for the enantioselective oxidation of dialkyl sulfides. 

Analytical Properties Resolution of several enantiomers of polycyclic aromatic hydrocarbons, for example, chrysene 5,6-epoxide, dibenz[a,h]anthracene 5,6-epoxide, 7-methyl benz[a]anthracene 5,6-epoxide resolution of barbiturates, mephenytoin, benzodiazepinones, and succinimides direct separation of some mono-ol and diol enantiomers of phenanthrene, benz[a]anthrene, and chrysene ionically bonded to silica gel, this phase provides resolution of enantiomers of c/s-dihydroidiols of unsubstituted and methyl- and bromo-substituted benz[a]anthracene derivatives having hydroxyl groups that adopt quasiequatorial-quasiaxial and quasiaxial-quasiequatorial conformation Reference 31-35... 

As shown in Scheme 7, lipase-assisted resolution of the racemic hydroxy ester ( )-45 allowed for isolation of chiral non-racemic enantiomer 45, which served to arrive at both diol 46 (via ester reduction) and all-cis epoxide 47 (via ferf-butylhydroperoxide treatment). In a remarkably flexible fashion, cyclopentene 46 was then used as the direct precursor of 3-methyl-branched P-D-ribocarbafuranose 48, P-D-... 

Procedure Capillary columns must be tested to ensure that they comply with the manufacturers specifications before they are used. These tests consist of the following injections a dilute methane sample to determine the linear flow velocity a mixture of alkanes (e.g., C14, C15, and Ci6) to determine resolution and a polarity test mixture to check for active sites on the column. The latter mixture may include a methyl ester, an unsaturated compound, a phenol, an aromatic amine, a diol, a free carboxylic acid, and a polycyclic aromatic compound, depending on the samples to be analyzed. 

For other anti-inflammation drugs such as Naproxen59 and Fenoprofen,60 only the S-isomer is biologically active. Since tedious resolutions are necessary to prepare these compounds, it would be desirable to develop a general asymmetric synthesis of the S(+) arylpropionic acids by microbial oxidation of pro-chiral substrates. This concept has been successfully applied in the preparation of a chiral metabolite of 29. Oxidation of one of the enan-tiotopic methyl groups in 30 with sulfurescens furnished the chiral diol 31.61 A similar oxidation of isobutyric acid (32)62 to S-(+)-3-hydroxy-2-mdthylpropionic acid (33) has been recently employed in the synthesis of the a-tocopherol synthon (34).63... 

Racemic hydroxy ester 225 was converted, via a Sharpless kinetic resolution, to the enantiomerically pure epoxide 226. This epoxide was then converted to the diol "/-lactone by intramolecular attack of the ester, assisted by nucleophilic dealkylation with iodide ion. Deprotonation and methylation anti to the alkoxide followed by acetonide formation afforded 227 in 56% yield. Dibal reduction, protection of the resulting aldehyde as the terminal olefin, silylation of the tertiary alcohol, and liberation of the aldehyde via ozonolysis provided a 45% yield of the C-9 to C-15 fragment 228. 

A new modification was recently described by Imamoto who employed a combination of (S,S)-2,2,5,5-tetramethyl-3,4-hexane diol (13) and Ti(OiPr)4 as catalyst. The active species was proposed to be monomeric with two diols and one cumyl hydroperoxide ligand leading to an octahedral coordination sphere around titanium. Under conditions similar to those reported by Kagan, p-tolyl methyl sulfoxide was obtained with 95% ee in 42% yield. Sulfone formation was a dominant, albeit beneficial side reaction giving in a kinetic resolution process (s=... 

In the chiral molecule 2,2,4-trimethyl-l,3-pentane-diol (Fig. 5.4), we note that CH3a and CH3b are not equivalent, and two peaks are seen. Even though the two methyl groups labeled c are not equivalent, they coincidently show only one peak. Two peaks may be seen at higher resolution. 

Resolution by transesterification. Using vinylic acetates to esterify allyl alcohols, propargyl alcohols, 2-phenylthiocycloalkanols, a-hydroxy esters," methyl 5-hydroxy-2-hexenoates, and 2-substituted 1,3-propanediols, the enantioselective esterification provides a means of separation of optical isomers. Vinyl carbonates are also resolved by lipase-mediated enantioselective conversion to benzyl carbonates. Other esters that have also been used in the kinetic resolution include 2,2,2-tri-fluoroethyl propionate. There is a report on a double enantioselective transesterification" of racemic trifluoroethyl esters and cyclic meso-diols by lipase catalysis. 

The 0-0 distances in the planar, zigzag conformation of 1,3-propane-diol and acyclic trans- and cfs-1,3-diols are 4.84, 3.43, and 2.51 A., respectively. By rotation about C-C bonds, these can be reduced to 1.74 A., when C-1, C-2, C-3, and the oxygen atoms are coplanar. Thus, with such compounds, the borate ion, B(0H)4 , would fit well, to form puckered, six-membered rings. The resolution of cis- Sa)[ Mo B) 0.18] and membered ring [(Sb) and (6b)] contains an axial alkyl group. 2-Methyl-1,3-pentanediol yielded, when subjected to electrophoresis, two components [ilf( (B) 0.08 and 0.24]. Presumably, the sub-... 

Xiong et al. also demonstrated that the chiral 2D framework [Cu(PPhj)(A,A( -(2-pyridyl-(4-pyridyl methyl)-amine)),5] C10 (9), with triangular cavities, synthesized from achiral components, [Cu(MeCN)j(PPh3)J[C10 ] and N,N -(2-pyridyl-(4-pyridyl methyl)-amine) can enantioselectively include 2-butanol [76]. Spontaneous resolution produced crystalline inclusion compound 91.5(2-butanol), which was structurally characterized. They manually separated the enantiomorphic forms of 91.5(2-butanol) according to their CD spectra in solid state and evacuated at 100°C to collect enantiopure 2-butanol. Although this work provides an economical route to enantioselective separation of racemic small diols, the separation... 

Optical Resolution of 3-Methylcycloalkanones and 5-Methyl-y -butyrolactone by Complexation with Optically Active 1,6-Bis(o-chlorophenyl)-1,6-diphenylhexa-2,4-diyne-l,6-diol... 

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