1
110
Chemistry Letters Vol.36, No.9 (2007)
Lipase-catalyzed Separation of Geometrical Isomers: Geraniol–Nerol
Ã
Pankaj Gupta, Subhash C. Taneja, Bhahwal A. Shah, Vijay K. Sethi, and Ghulam N. Qazi
Indian Institute of Integrative Medicine (CSIR), Canal Road, Jammu-180001, India
(Received June 4, 2007; CL-070594; E-mail: sc taneja@yahoo.co.in)
The substrate/lipase ratio as well as pH of the buffer medi-
um played important roles in the resolution of geometrical iso-
meric mixture of geraniol–nerol. Based on the results, an immo-
bilized lipase from Pseudomonas fluorescens (PFL) was found
effective in selective transesterifications whereas Pseudomonas
sp. Lipase (PSL) was found to be useful in hydrolyzing the
esters.
R O/Py
2
OH
OR
R = Ac, E = 64%,
Z = 36%
R = Pr, E = 65.3%
Z = 34.7%
E = 63%
Z = 37%
Transesterification
Hydrolysis
Geraniol and nerol (trans and cis isomers of 3,7-dimethyl-
,6-octadiene-1-ol) are acyclic monoterpene primary alcohols
OAc
OH
2
1
and the important constituents of a number of aromatic plants.
Besides, their use in food and flavour industry these alcohols are
R = Ac, E > 95%,
Z < 05%
R = Pr, E > 99%
E > 88%
Z < 12%
2
used for the synthesis of Vitamins A and E. Geraniol also called
rhodinol, is the primary constituent of the oil of rose and palmar-
osa, and is associated with a sweet rose-like odor, for which it is
commonly used in perfumes. High content of geraniol is mainly
responsible for the characteristic odor of palmarosa oil, which
has its use as antiseptic, mosquito repellent, and pain relieving
Scheme 1. Lipase-catalyzed transesterification and hydrolysis.
experimental conditions of pH, temperature, and substrate:lipase
ratios.
In the course of biocatalytic approach, we were able to
achieve the separation of two geometrical isomers with moderate
to high selectivity. The various microorganisms used in the pres-
ent study include Trichosporon beigilli (DSMZ 11829), Arthro-
bacter sp. (MTCC no. 5125), Aspergillus niger (Lipase AS,
Amano), Mucor miehi (MM), Pseudomonas sp. (PS), Candida
crusie (CC), Candida rugosa (CR), etc.
3
agent. Different biological activities have been attributed to
geraniol and its geometrical isomer nerol. The trans isomer
4
has modest in vitro and in vivo immunosuppressive activity
and also inhibits the growth and polyamine biosynthesis in
5
,6
human colon cancer cells.
Geraniol reportedly inhibited
7
MCF-7 proliferation in human breast cancer cells. It also inhib-
ited HMG-CoA (3-hydroxy-3-methylglutaryl Coenzyme A) re-
ductase activity as the increase in HMG-CoA reductase activity
is characteristic of a tumor type. Geraniol is also capable of po-
tentiating the anti tumor effect of 5-florouracil.9
Table 1. Enzyme-catalyzed hydrolysis of (E/Z) geranyl/neryl
Ã
acylates using PSL
8
Time Convn
Substrate
Solvent (1:5)
ACN:Buffer
Acetone:Buffer 87.6:12.4 71
E:Z
/h
/%
The Z isomer nerol is a starting material for the synthesis
of nerol oxide,10 an important perfumery material. The small
Geranyl
acetate
95.6:4.4
71
42
50
ꢀ
difference in boiling points (nerol 227–228 C and geraniol
ꢀ
229–230 C) makes their separation more cumbersome even
(
E/Z)
DMSO:Buffer
Methanol:Buffer 90.2:9.8
85:15
71
71
71
49
60
35
45.7
36
38
49.5
45.7
18
if an efficient fractional distillation method may be used for their
separation. Though, biocatalytic methods including hydrolases
have extensively been used for the resolution of racemic
mixtures, however, their application in the separation of geomet-
Geranyl
propionate
(
ACN:Buffer
ACN:Buffer
ACN:Buffer
>99
82.3:17.7 71
96:4
a
E/Z)
120
71
120
71
41
41
1
1
rical isomers has been uncommon as well as less effective. In
the present study, we envisaged to exploit the biocatalytic route
for the separation of the cis and trans isomers. An earlier attempt
to resolve a mixture of geraniol and nerol, was achieved via
selective acylation with acid anhydrides in the presence of
Acetone:Buffer >99
Acetone:Buffer 93:7
Methanol:Buffer 90.1:9.9
Geranyl
butyrate (E/Z) ACN:Buffer
ACN:Buffer
>99
80:20
a
21.8
1
2
Porcine pancreatic lipase (PPL) as a catalyst. However, they
were able to achieve only a partial separation resulting in enrich-
ment level of 90:10 of E:Z isomers. In this communication,
results of our attempts towards the development of a more
efficient method of kinetic resolution of geometrical isomers
are presented (Scheme 1).
For the kinetic resolution studies, a panel of lipases belong-
ing to institute’s repository as well as procured from commercial
sources, were used for the selective hydrolysis of various
acylates of natural geraniol–nerol mixture (63:37) under varying
Ã
ꢀ
All the reactions were performed at 20–22 C, Quantity of
lipase (w/w) = 1:49. a, 1:19. Product was analyzed by in-
jecting a 0.5-mL aliquot in a split less mode into a gas–liquid
chromatograph (GLC) equipped with a flame ionization de-
tector. A BP-10 fused silica capillary column heated isother-
ꢀ
mally at 170 C was used to separate and identify the prod-
ucts. Injector and detector temperatures were set at 250 and
2
flow rate of 5 mL/m. Product yield and selectivity were cal-
culated using peak area integration by an on-line computer.
ꢀ
60 C respectively. Helium was the carrier gas with a total
Copyright ꢀ 2007 The Chemical Society of Japan