Page 153 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

140 hydrolysis, oxidation and reduction

10.2 ENANTIOSELECTIVE SYNTHESIS OF
(Z)-N-CARBOBENZYLOXY-3-HYDROXYPROLINE ETHYL ESTER

Mukund P. Sibi and James W. Christensen
Department of Chemistry, North Dakota State University, Fargo ND, 58105-5516, Sibi@-
plains.nodak.edu

10.2.1 IMMOBILIZATION OF BAKERS' YEAST

Materials and equipment
. Supermarket variety bakers' yeast, 20 g [5]
. Sodium alginate, 5 g
. Water, 200 mL
. 10 % (w/v) Calcium chloride, 670 mL

. 2 L Erlenmeyer flask
. Magnetic stirrer
. 1 L Dropping funnel

Procedure

1. Two separate solutions of Red Star active dry yeast (or other supermarket
variety, 20 g) and sodium alginate (5 g) each in water (200 mL) were pre-
pared by very slow addition of the respective reagent to the rapidly stirred
solvent.
2. When each solution became an homogeneous viscous fluid, they were com-
bined and added dropwise via an addition funnel to calcium chloride
(670 mL of 10 % (w/v)). The droplets formed gelatinous beads upon impact
with the salt solution. The size and shape of the beads may be adjusted by
the rate of addition.
3. The beads were washed five times with water (portions of 500 mL), and used
immediately in the reduction of ketone.

10.2.2 BAKERS' YEAST REDUCTION OF
(Z)-N-CARBOBENZYLOXY-3-KETOPROLINE ETHYL ESTER

O OH
,
OEt Bakers Yeast OEt
N N
O O
O O O O