p-Toluenesulfonic acid monohydrate → D-Alanine trans-2-Methylcyclohexyl Ester p-Toluenesulfonate

Participants

Reaction Steps

N-Benzyloxycarbonyl-D-alanine-trans-2-methylcyclohexyl ester (14.7 g, 47.5 mmol) and p-toluenesulfonic acid monohydrate (9.04 g, 47.5 mmol) were dissolved in 135 mL MeOH. The methanolic solution was hydrogenated over 2.51 g of 10% Pd/C at 40 psi in a Parr apparatus for 1 hour. The catalyst was removed by filtration through a Celite pad and the filtrate was concentrated under reduced pressure. The salt was precipitated by addition of ether. Yield: 13.8 g in 2 crops (81%) mp 145°-147°. Tlc on silica gel (CHCl3 :MeOH:HOAc=45:5:1) indicated a single ninhydrin positive spot. 250 MHz nmr (CD3OD, ppm) 0.92 (d, 3H, J=6.25 Hz, trans-2-methyl), 1.09-1.99 (m, 7H, aliphatic cyclohexyl protons), 1.53 (2d, 3H, β--CH3 of Ala), 2.37 (s, 3H, CH3 --Ar--SO3H), 4.09 (2q, 1H, J=7.35 Hz, 2.57 Hz; α--H of Ala), 4.51 (m, 1H, α--H of alcohol); 7.22, 7.69 (ABq, 4H, J=8.46 Hz, CH3 --ArH4 --SO3H).

Provenance & Evidence