ENZYMATIC SYNTHESES OF N-LAUROYL-β-ALANINE HOMOLOGS
877
Compound 3b was hydrolyzed by refluxing for 6 h with 2a (Table 1, entries 1 and 2). Furthermore, in the lipase-cat-
20% aqueous potassium hydroxide solution (5 mL) and ethyl- alyzed transesterification of alcohols with vinyl esters, the ad-
ene glycol monomethyl ether (10 mL), and afforded N-lauroyl- dition of molecular sieves has a dramatic effect on the reac-
β-alanine (3d), m.p. 109–110°C [lit. (14) m.p. 108–110°C] in tion rate and chemical yields (16,17). In the CAL-catalyzed
85% yield.
amidation of 1a in the presence of molecular sieves, the reac-
Reaction of the ester 2b with β-alanine ethyl ester 1b cat- tion rate was not significantly different from that in the ab-
alyzed by CAL. When β-alanine ethyl ester was used after sence of molecular sieves. However, the chemical yield was
converting to free amine, the yield was 30% down. Therefore, higher than that without molecular sieves (entry 3). The ef-
when β-alanine ethyl ester (1b) was used in the hydrochlo- fect can be explained on the basis of molecular sieves adsorb-
ride salt form, an equimolar sodium hydroxide aqueous solu- ing some unknown impurity, produced in a side reaction,
tion was necessary to convert to free amine during enzymatic which disturbs the amidation. The CAL-mediated reaction of
reaction. In an Erlenmeyer flask, ester 1b (5 mmol) and ester 1a (1 equiv.) with 2b (1 equiv.) at 24°C for 24 h proceeded to
2
b (5 mmol) in the appropriate solvent (20 mL) were mixed afford 3b with higher yield (entry 5), compared with that in
with 1 mL of sodium hydroxide aqueous solution (5 M/L), the CAL-catalyzed reaction of 1a (1 equiv.) with 2b (2 equiv.)
and CAL (0.5 g) was added. The procedures for 3-aminopro- (entry 2). Moreover, yields of enzymatic reactions of
pionitrile 1a as described above were followed.
equimolecular amounts of 1a and 2b were not affected by a
N-Lauroyl-β-alanine ethyl ester (3c). This compound was change in the reaction temperature (entries 4–7). After 24 h
obtained by the enzymatic amidation of 1b with 2b; colorless of reaction in diisopropyl ether, the enzyme does not lose its
crystals, m.p. 45–46°C IR (KBr): 3300 (-NH), 1730 (ester), catalytic activity and can be reused six times (entries 8–12).
−
1
1
1
630, 1545 cm (-NHCO-). H NMR: δ = 0.92 (t, 3H, -CH
CAL can be reutilized without any subsequent treatment and
3
of lauroyl group), 1.26 (m, 18H, -CH -), 1.34 (t, 3H, -CH of with little los of activity.
2
3
ester group), 2.15 (t, 2H, -CH CON-), 2.51 (t, 2H, -CH COO-),
The CAL-catalyzed reaction of equimolar amounts of 1b
2
2
3
1
.54 (d-d, 2H, -CH N-). 4.11 (q, 2H, -CH OOC-) 6.10 (br-s, and 2b in various organic solvents (entries 13–16) resulted in
H, -NH). MS: m/z 299 (M ). Elemental analyses: C, 68.07; the formation of N-lauroyl-β-alanine ethyl ester (3c). Among
2
2
+
H, 11.03; N, 4.86%; 1 calculated for C H NO :1 C, 68.19; the organic solvents tested, dioxane was the best (entry 16).
1
7
33
3
H, 11.11; N, 4.68%.
The reaction of 1b with 2b was less complete than that of 1a
The hydrolysis of 3c with 10% aqueous potassium hydrox- with 2b (entries 5 and 16). It is not clear if this is due to the
ide solution (5 mL) and ethylene glycol monomethyl ether difference in the substrates or the difference in the solvents
(
10 mL) after 3 h refluxing afforded 3d in 80% yield.
used in the two reactions. Because 1b did not dissolve in di-
isopropyl ether, it was not possible to compare the two reac-
tions in that solvent.
RESULTS AND DISCUSSION
The hydrolysis of 3c with 10% aqueous potassium hydrox-
Candida antarctica lipase (CAL) has been widely used for ide solution and ethylene glycol monomethyl ether afforded
the amidation of esters and amines (9–12). Our interest in de- 3d.
veloping improved methods for the preparation of N-lauroyl-
Neither the enzymatic reaction of diethyl glutamate (1c)
β-alanine led us to examine the enzymatic amidation of 1a nor N-methylglycine ethyl ester (1d) with 2b by means of
and 1b with the esters 2a or 2b by CAL. Our results for this CAL afforded amidation products (entries 17 and 18). These
enzymatic amidation by means of CAL are summarized in results show that the CAL enzyme catalyzes reactions only
Table 1. The amine 1a (1 equivalent) was incubated with with nonbulky primary amines. This fact suggests that the
CAL and the ester 2a (2 equiv.) in diisopropyl ether at 24°C presence of the bulky group in the α-position of the amine
for 48 h, resulting in the formation of 3-(caproylamino)propi- hinders adequate fitting of the substrates or product on the
onitrile (3a) in 82.6% yield (entry 1 in Table 1). Similarly, the catalytic site of the enzyme.
reaction of 1a (1 equiv.) with 2b (2 equiv.) and CAL at 24°C
Results similar to ours have been obtained by Goto and co-
for 24 h resulted in the formation of 3-(lauroylamino)propi- workers who have reported that CAL efficiently catalyzes the
onitrile (3b) in 84.9% yield (entry 2). Hydrolysis of 3b with preparation of β-ketoamides from β-ketoesters with primary
aqueous potassium hydroxide solution afforded N-lauroyl-β- aliphatic amines and ammonia (10).
alanine (3d). In these studies, and in all work reported here,
no product was formed if enzyme was not present in the reac-
tions.
ACKNOWLEDGMENTS
T. Izumi gratefully thanks Kawaken Fine Chemicals Co. for partial
financial support and for the gifts of β-alanine hydrochloride, methyl
caproate, and methyl laurate.
Previously, Wang and coworkers (15), in studies of the en-
zymatic transesterification of alcohols with vinyl esters as
acylating agents by means of lipase, reported that long-chain
esters were generally faster than short-chain esters. In the en-
zymatic amidation of 1a with esters and CAL, we also found REFERENCES
that the rate of amidation with the longer-chain ester 2b is
1
. Fox, C., Advances in Cosmetic Science and Technology. IV.
about two times faster than that with the shorter-chain ester
Cosmetic Vehicles, Cosmet. Toiletries 110:59–62 (1995).
JAOCS, Vol. 74, no. 7 (1997)
Izumi
