3.5- Dimethylphenylcarbamate, optical resolution

Figure 3.4 Optical resolution of 19 on cellulose tris(3,5-dimethylphenylcarbamate) column 25 x 0.46 (i.d.) cm eluent hexane/2-propanol (90/10) flow rate 0.5 ml/min (i.d. = inside diameter).

Okamoto, Y., Aburatani, R., Kaida, Y., and Hatada, K. (1988) Direct optical resolution of carboxylic acids by chiral HPLC on tris(3,5-dimethylphenylcarbamate)s on cellulose and amylose, Chem. Lett., 1125-1128. 

Hopf, H., Grahn, W., Barrett, D.G., Gerdes, A., Hilmer, J., Hucher, J., Okamoto, Y., and Kaida, Y. (1990) Optical resolution of [2.2]paracyclophanes by high-performance liquid chromatography on tris(3,5-dimethylphenylcarbamate) of cellulose and amylose, Chem. Ber. 123, 841-845. 

Lacroix et al. compared an HPLC with a H NMR method for quantification of the R-enantiomer in S-timolol maleate, a -blocking substance (Figure 6-7) [17]. For satisfactory resolution, the HPLC required the expensive cellulose tris-3,5-dimethylphenylcarbamate column (Chiracel OD-H), a mobile phase of 0.2% dimethylamine and 4% isopropano in hexane and H NMR (400-MHz) R-TFAE as a CSA in CDCIj. The resonance of the tert-butyl group between 1.0 and 1.1 ppm was used to measure the ee. With both methods, 0.2- 4.0% of the R-enantiomer in S-timolol could be determined precisely. Additionally, both methods (HPLC and NMR) were found to be superior to specific rotation, which is used in the USP XXIII for determination of optical purity. This superiority of NMR and HPLC methods over optical rotation has often been reported [2],... 

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