Efficient chemoenzymatic synthesis of phenylacetylrinvanil: An ultrapotent capsaicinoid

Article abstract of DOI:10.1055/s-0028-1083521

The straightforward synthesis of phenylacetylrinvanyl (PhAR), an ultrapotent capsaicinoid is described. The process starts with the quantitative synthesis of methyl ricinoleate (MeRic) by castor oil methanolysis. Afterwards, two alternative routes are pos

Full text of DOI:10.1055/s-0028-1083521

LETTER
2869
Efficient Chemoenzymatic Synthesis of Phenylacetylrinvanil: An Ultrapotent
Capsaicinoid
C
hemoenzymat
d
ic Synthesis
m
of
P
henylacetylrinv
u
anil ndo Castillo,*a Ignacio Regla,*b Patricia Demare,b Axel Luviano-Jardón,b Agustín López-Munguíaa
a
Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Apdo. Postal 510-3, Cuernavaca, Morelos 62271,
Mexico
Fax +52(73)172388; E-mail: edmundo@ibt.unam.mx
Facultad de Estudios Superiores-Zaragoza, UNAM, Batalla del 5 de Mayo esq. Fuerte de Loreto, Ejercito de Oriente, 09230 México,
b
D.F., México
E-mail: regla@unam.mx
Received 27 April 2008
analogues that could bind the TRPV1 receptor with high
specificity but with reduced pungency would lead to more
effective drugs for the treatment of health disorders such
as inflammatory hyperalgesia, bladder hyperactivity,
Abstract: The straightforward synthesis of phenylacetylrinvanyl
(PhAR), an ultrapotent capsaicinoid is described. The process starts
with the quantitative synthesis of methyl ricinoleate (MeRic) by
castor oil methanolysis. Afterwards, two alternative routes are pos-
sible: a) chemoselective vanillylamine aminolysis of MeRic cata- emesis, cancer growth, neuronal excitotoxicity, pain, and
dysmotility.5 In fact, it has been shown that analogues of
lyzed by Candida antarctica lipase-B (CaLB) to yield rinvanil,
which after reaction with phenylacetic acid and DCC–DMAP fol-
capsaicin, which do not irritate the skin, such as capsiate
lowed by a regioselectively pyrrolidine deacylation results in PhAR
(2) and olvanil (3) (Figure 1), strongly activate TRPV1 in
with a 51% global yield, b) methyl 12-phenylacetylricinoleate syn-
vitro and have in vivo antihyperalgesic effects.6,7
thesis by reaction of MeRic with phenylacetic acid and DCC–
DMAP, followed by a chemoselective vanillylamine aminolysis
catalyzed by CaLB to obtain PhAR with a 70% global yield.
O
OMe
Key words: chemoselective synthesis, solvent effects, enzymes,
Candida antarctica B, ultrapotent capsaicinoid
N
H
OH
capsaicin (1)
O
Transient receptor potential vanilloid type 1 (TRPV1) is a
vanilloid receptor highly expressed in sensory neurons.1
This protein acts as a rapid and direct detector of poten-
tially harmful thermal and chemical stimuli, which are
perceived as painful. Activation of this receptor, potenti-
ated by endogenous pronociceptive mediators such as
prostaglandins, bradykinin, and ATP, results in a release
of neurotransmitters from peripheral and central nerve ter-
minals, inducing pain and neurogenic inflammation, thus
playing an important role in neuropatic pain, intestinal in-
flammation, and other disorders.2,3
OMe
OH
O
capsiate (2)
O
OMe
OH
N
H
olvanil (3)
Figure 1 Chemical structures of capsainoids TRPV1 agonists
Recently, the synthesis of phenylacetylrinvanil (4, PhAR,
IDN 5890, Figure 2), an ultrapotent TRPV1 agonist with
moderate affinity for human cannabinoid CB2 receptors,
has been described.5 In terms of its affinity for the recep-
tor, PhAR was found similar to resiniferatoxin (5)
(Figure 2), a natural product isolated from certain succu-
lent African euphorbias, about 1000 times more potent as
a TRPV1 agonist than capsaicin,8 that has been success-
fully applied in the treatment of urinary incontinence.9 It
is interesting to observe that the high affinity of PhAR re-
sults from the simple phenylacetylation of 12-hydroxyl
group in rinvanil (6) (Scheme 1).
Capsaicin (E)-N-[(4-hydroxy-3-methoxyphenyl)methyl]-
8-methyl-6-nonenamide (1, Figure 1) is a compound
found in the fruit of plants of the Capsicum genus and is
responsible for the pungency of chilli peppers. Due to its
exogenous effect as agonist of TRPV1 channels, capsaicin
has been widely used to study pain mechanisms and to
evaluate the analgesic efficacy of various drugs. While
initial exposure to capsaicin results in pain and hyperalge-
sia, repeated or prolonged treatment with capsaicin can
desensitize nociceptive neurons, leading to a progressive
decrease in subsequent responses to capsaicin or to other
stimuli.4 In spite of its pungency, this functional desensi-
titation is the basis of the topical analgesic and anti-in-
flamatory effect of capsaicin. The discovery of new
Appendino et al. (2005) have proposed two strategies for
the chemical synthesis of PhAR: starting from expensive
pure ricinoleic acid, the protection of the carboxyl group
with trichloroethanol (DCC–DMAP), followed by acyla-
tion with phenylacetic acid–DCC–DMAP at 12-hydroxy
position of trichloroethyl ester, deprotection of trichloro-
SYNLETT 2008, No. 18, pp 2869–2873
1
4
.1
1
.2
0
0
8
Advanced online publication: 01.10.2008
DOI: 10.1055/s-0028-1083521; Art ID: S03708ST
© Georg Thieme Verlag Stuttgart · New York

2870
E. Castillo et al.
LETTER
O
ethyl ester, and amide formation with vanillylamine using
a cyclic anhydride protocol, to obtain PhAR with a global
yield of 18.5%.5 Their alternative proposal (Scheme 1)
consists in the esterification of rinvanil (6) with phenyl-
acetic acid using DCC–DMAP in toluene, to obtain 7, the
4′,12-diester of rinvanil, which can be regioselectively hy-
drolyzed (pyrrolidine, CH2Cl2) to give PhAR (4).10
OMe
OH
N
H
O
phenylacetylrinvanil (4)
O
In the present work, a chemoenzymatic strategy for the
synthesis of PhAR from commercially available castor oil
is described (Scheme 2). This regio- and chemoselective
strategy not only allows higher global PhAR yields but
also results in a more economical process as it involves
the use of castor oil as a not expensive source of ricino-
leoyl moiety in the form of easily purified methyl ester,
therefore, avoiding the difficult task of ricinoleic acid pu-
rification (Scheme 2).
O
O
O
H
resiniferatoxin (5)
H
H
O
OMe
OH
O
O
OH
Figure 2 Chemical structures of resiniferatoxin and phenylacetyl-
rinvanil
Indeed, the production of methyl ricinoleate (8), the first
step of PhAR synthesis, was actually explored from a me-
dium containing castor oil (20 g) in MeOH (155 mL) by
O
CO2H
OMe
O
O
N
H
OMe
N
H
DCC, DMAP
7
OH
6
O
O
OH
O
O
NH
CH2Cl2
OMe
OH
N
H
O
4
O
Scheme 1 Chemical synthesis of PhAR from rinvanil (6)5
O
OMe
OH
N
H
OH
6
a) PhCH2CO2H, DCC, DMAP
b) C4H9N
castor oil
KOH
MeOH
vanillylamine
CaLB
51%
O
O
OMe
OH
N
H
OMe
4
O
8
OH
O
PhCH2CO2H, DCC
DMAP
O
vanillylamine
CaLB
OMe
70%
O
9
O
Scheme 2 Alternative syntheses of PhAR from castor oil using a chemoenzymatic approach
Synlett 2008, No. 18, 2869–2873 © Thieme Stuttgart · New York

LETTER
Chemoenzymatic Synthesis of Phenylacetylrinvanil
2871
two alternative catalytic methods of alcoholysis: an enzy- approach, the acid function in the ricinoleic acid is pro-
matic reaction with 10 mg/mL of Candida antarctica li- tected as a methyl ester, allowing in a first step a straight
pase B (CaLB) and a chemically catalyzed reaction with and efficient esterification with phenylacetic acid at the
KOH (Scheme 2). Although an 80% yield was obtained 12-hydroxy position; subsequently, the chemoselective li-
through the CaLB reaction after 24 hours of reaction, only pase-catalyzed amidation of the methylated carboxyl
30 minutes under reflux was required with the KOH reac- group of 9 is highly favored by the specificity of CaLB
tion to obtain a quantitative mixture of methyl esters, and the higher nucleophilicity of primary amino group
which, after column chromatography, resulted in a 85% than that of phenol of vanillylamine. Actually, we have
yield of 8 (16.67 g), equivalent to 95% yield of methyl ri- previously demonstrated that the acylation of phenolic
cinoleate on the basis of available ricinoleic acid on castor group of vanillylamine does not take place at all in this
oil (87%). The KOH-catalyzed alcoholysis was therefore kind of reactions.14 Finally, it is also important to under-
the best option. Furthermore, while optimizing the re- line that based on thermodynamic assumptions, the use of
quired amount of KOH for the reaction, it was possible to a polar solvent such as dry 2-methyl-2-butanol and an ex-
reduce it to 0.28% w/v retaining the same yield and pro- cess of diester 9 favors a high yield of amide synthesis.15
ductivity. This is, to our knowledge, the lowest KOH con- The spare diester was easily recovered during PhAR puri-
centration reported for the preparation of fatty acid methyl fication. To the best of our knowledge, this is the first ex-
esters.11
ample of a chemo- and regioselective enzymatic
aminolysis of hydroxylated fatty acid diesters.
The complexity of synthesis of vanillylamides relies on
the low chemoselectivity of the acylation process, due to In summary, the chemoenzymatic strategy here described
the presence of both an amino and a phenolic hydroxyl results in a valuable alternative for the synthesis of the ul-
group on the vanillylamine molecule. For instance, trapotent capsaicinoid phenylacetylrinvanil (4), allowing
equimolar amounts of vanillylamine and oleic acid in the to envisage a general method for the synthesis of these
presence of DCC and DMAP result in a mixture of the valuable compounds. Indeed, in contrast to chemical
amide (olvanil) and the ester (O-oleylolvanil), as well as methods, the chemo- and regioselective properties of li-
unreacted vanillylamine.12 Therefore, protection of the pase-catalyzed reactions allowed higher yields of 4, con-
phenolic group of vanillylamine is required when the acid firming the high potential of enzymatic processes to
is activated as a hydroxysuccinimide derivative or as a impact traditional chemical synthetic routes. In addition,
mixed anhydride13 and although Schotten–Baumann con- the use of castor oil, a renewable and widely available
ditions are usually selective, acid chlorides are needed for source of ricinoleoyl moiety, renders this process feasible
this strategy. An interesting alternative proposed for the for large-scale application of PhAR synthesis and its de-
synthesis of PhAR that does not require the phenolic pro- rivatives.
tection of vanillylamine is the use of propylphosphoric an-
hydride; however, this process results in a low PhAR yield
(35%).12 In order to overcome these limitations, we devel-
Typical Procedure of the Chemical Aminolysis for the Synthesis
of 12-Phenylacetylrinvanil (4)17
oped two chemoenzymatic approaches taking advantage
of the high regio- and chemoselectivity of the lipase-cata-
lyzed aminolysis. The first approach consists in the
chemoselective enzymatic amidation of 8 (2 g, 6.4 mmol)
with CaLB (9 mg/mL) and vanillylamine (1.21 g, 6.4
mmol) at 37 °C, to obtain rinvanil (6, 1.94 g, 70% yield)
(Scheme 2). The enzymatic amidation proceeds with high
regio- and chemoselective specificity as the amide 6 is the
only product observed in the synthesis. In the next step, 6
(0.330 g, 0.76 mmol) is acylated with 2.2 equivalents of
phenylacetic acid–DCC–DMAP to produce 12,4′-diphe-
nylacetyl rinvanil (7, 0.390 g, 76.5% yield). Finally, the
phenolic group of 7 (0.360 g, 0.5 mmol) is deacylated
with pyrrolidine and CH2Cl2 (186 mL, 2.29 mmol) to pro-
duce PhAR (4, 0.285 g, 96.28% yield) with a global yield
of 51% from 8 (Scheme 2).
To a solution of 12,4′-diphenylacetylrinvanil (7, 360 mg, 0.5 mmol)
in CH2Cl2 (25 mL), pyrrolidine (186 mL, 2.29 mmol, 5 mol equiv)
was added. The reaction mixture was stirred at r.t. for 6 h (TLC,
hexane–EtOAc, 6:4); 2 N H2SO4 (2.29 mL) was added, the organic
layer separated, and the aqueous layer (pH = 4–5) extracted (2 × 5
mL) with CH2Cl2. The organic extract was washed with H2O (2 × 5
mL) and brine (5 mL), dried with Na2SO4, and concentrated to dry-
ness to yield 550 mg of raw product, purified by column chromatog-
raphy (70–230 mesh; 9 g silica gel; hexane–EtOAc, 7:3) to yield
285 mg (96.28%) of pure 4. Due to the recognized ultrapotent activ-
ity of this compound in case of skin contact (very irritant), it is high-
ly recommended the use of splash goggles and gloves when
handling this material.
1H NMR (300 MHz, CDCl3): d = 0.86 (t, J = 7.2 Hz, 3 H), 1.19–
1.32 (m, 16 H), 1.46–1.54 (m, 2 H), 1.63 (q, J = 7.2 Hz, 2 H), 1.94
(c, J = 6.3 Hz, 2 H), 2.18 (t, J = 7.8 Hz, 2 H), 2.23–2.32 (m, 2 H),
3.57 (s, 2 H), 3.84 (s, 3 H), 4.32 (d, J = 5.4 Hz, 2 H), 4.86 (q, J = 6.6
Hz, 1 H), 5.22–5.31 (m, 1 H), 5.38–5.47 (m, 1 H), 5.83 (br t, J = 4.5
Hz, 1 H), 6.73 (dd, J1 = 7.8 Hz, J2 = 2.1 Hz, 1 H), 6.78 (d, J = 1.8
Hz, 1 H), 6.86 (d, J = 8.1 Hz, 1 H), 7.20–7.33 (m, 5 H). 13C NMR
(75 MHz, CDCl3): d = 14.0, 22.4, 25.1, 25.6, 27.2, 29.01, 29.04,
29.13, 29.16, 29.4, 31.6, 31.8, 33.4, 36.7, 41.7, 43.4, 55.8, 74.5,
110.6, 114.3, 120.7, 124.0, 126.9, 127.0, 128.4, 128.5, 129.1, 129.2,
130.2, 132.5, 145.0, 146.6, 171.3, 173.0. MS (EI): m/z (%) = 551
(30) [M+], 415 (41), 277 (13), 152 (64), 137 (100), 91 (22). IR
(film): nmax = 3362, 3306, 2928, 2856, 1729, 1646, 1517, 1274,
In our second approach, the synthesis is now started with
the phenylacetylation of 8 (13.5 g, 43 mmol) with phenyl-
acetic acid–DCC–DMAP (11.66 g, 85.7 mmol) to yield
methyl 12-phenylacetylricinoleate (9, 16.37 g, 88%
yield), followed by the enzymatic amidation of 9 (2 g, 4.6
mmol) with vanillylamine (0.190 g, 1 mmol) by CaLB (35
mg/mL) to produce PhAR (4, 434 mg, 79% yield) with a
global yield of 70% from 8 (Scheme 2). In this simplified
Synlett 2008, No. 18, 2869–2873 © Thieme Stuttgart · New York

2872
E. Castillo et al.
LETTER
1034, 721, 700 cm–1. [a]D20 +15.2 (c 1, MeOH); lit.5 [a]D20 +35.6 (c
1.1, MeOH).
3.57 (s, 2 H), 3.71 (s, 3 H), 3.87 (s, 2 H), 4.34 (d, J = 5.8 Hz, 2 H),
4.86 (q, J = 6.0 Hz, 1 H), 5.24–5.32 (m, 1 H), 5.40–5.49 (m, 1 H),
5.93 (br t, J = 4.2 Hz, 1 H), 6.76 (dd, J1 = 7.9 Hz, J2 = 1.9 Hz, 1 H),
6.84 (d, J = 1.7 Hz, 1 H), 6.91 (d, J = 7.9 Hz, 1 H). 13C NMR (75
MHz, CDCl3): d = 14.1, 22.6, 25.2, 25.8, 27.3, 29.1, 29.2, 29.3,
29.4, 29.6, 31.7, 32.0, 33.6, 36.7, 41.0, 41.85, 43.4, 55.9, 74.6,
112.2, 120.0, 122.7, 124.2, 127.0, 127.3, 128.5, 128.6, 129.3, 129.4,
132.7, 133.6, 134.4, 137.6, 139.2, 151.2, 169.7, 171.4, 173.1.
Typical Procedure of the Enzymatic Aminolysis for the Prepa-
ration of 12-Phenylacetylrinvanil (4)
Vanillylamine·HCl (190 mg, 1 mmol) was suspended in dry 2-me-
thyl-2-butanol (20 mL) containing 4 Å MS (500 mg) and Et3N (840
mL). The mixture was agitated 30 min at 30 °C and 250 rpm. Then,
methyl 12-phenylacetylricinoleate (2 g, 4.6 mmol) and CaLB (750
mg) was added, and the mixture was incubated at 30 °C. The reac-
tion was monitored by TLC (hexane–EtOAc, 1:1; ninhydrine as vi-
sualizing reagent). Filtration over Celite and vacuum concentration
afforded 434 mg of 4 (78.7% yield based on the vanillylamine·HCl)
and 1.55 g of pure methyl 12-phenylacetylricinoleate after silica gel
chromatography.
Methyl ricinoleate (8)
Castor oil (20 g) was dissolved in MeOH (155 mL) and heated un-
der reflux for 30 min in the presence of solid KOH (58 mg, 0.28%).
At the end of the reaction (TLC, hexane–EtOAc, 85:15) AcOH (80
mL) was added, and the mixture was evaporated to dryness under
reduced pressure. The residue was redissolved in hexane (30 mL)
and washed with H2O (2 × 25 mL) and with sat. NaCl solution
(1 × 25 mL). The organic phase was dried with anhyd Na2SO4 and
concentrated under reduced pressure, hence, 20.3 g of crude product
afforded 16.67 g of 8 (85% yield) after column chromatography
(400 g silica gel, hexane–EtOAc, 9.5:5 to 9:1 gradient). Purity of 8
(99% pure) was established by HPLC in a Waters HPLC system
equipped with a Waters Symmetry C18 4.6 × 250 mm, 5 mm col-
umn (Milford, MA, USA) eluted with 1.5 mL/min of 85:15 MeCN–
H2O and using a refractive index detector at 35 °C; tR = 6.45 min.
[a]D +15.2 (c 1, MeOH); Lit.5 [a]D +35.6 (c 1.1, MeOH). IR
(film): 3362, 3306, 2928, 2856, 1729, 1646, 1517, 1274, 1034, 721,
700 cm–1. 1H NMR (300 MHz, CDCl3): d = 0.86 (t, 3 H, J = 7.2 Hz),
1.19–1.32 (m, 16 H), 1.46–1.54 (m, 2 H), 1.63 (q, 2 H, J = 7.2 Hz),
1.94 (c, 2 H, J = 6.3 Hz), 2.18 (t, J = 7.8 Hz, 2 H), 2.23–2.32 (m, 2
H), 3.57 (s, 2 H), 3.84 (s, 3 H), 4.32 (d, J = 5.4 Hz, 2 H), 4.86 (q,
J = 6.6 Hz, 1 H), 5.22–5.31 (m, 1 H), 5.38–5.47 (m, 1 H), 5.83 (br
t, J = 4.5 Hz, 1 H), 6.73 (dd, J1 = 7.8 Hz, J2 = 2.1 Hz, 1 H), 6.78 (d,
20
20
J = 1.8 Hz, 1 H), 6.86 (d, J = 8.1 Hz, 1 H), 7.20–7.33 (m, 5 H). 13
C
NMR (75 MHz, CDCl3): d = 14.0, 22.4, 25.1, 25.6, 27.2, 29.01,
29.04, 29.13, 29.16, 29.4, 31.6, 31.8, 33.4, 36.7, 41.7, 43.4, 55.8,
74.5, 110.6, 114.3, 120.7, 124.0, 126.9, 127.0, 128.4, 128.5, 129.1,
129.2, 130.2, 132.5, 145.0, 146.6, 171.3, 173.0. MS (EI): m/z (%) =
551 (30) [M+], 415 (41), 277 (13), 152 (64), 137 (100), 91 (22).
[a]D20 +7.4 (c 1, MeOH), +3.33 (c 1.5, CHCl3); Lit.16 [a]D20 +3.4 (c
1.5, CHCl3). IR (film): 3435, 2928, 2856, 1742, 1439, 1173, 859,
725 cm–1. 1H NMR (400 MHz, CDCl3): d = 0.89 (t, J = 6.8 Hz, 3 H),
1.29–1.33 (m, 16 H), 1.45–1.50 (m, 2 H), 1.62 (q, J = 7.2 Hz, 2 H),
2.04 (c, J = 6.4 Hz, 2 H), 2.21 (t, J = 6.4 Hz, 2 H), 2.30 (t, J = 7.6
Hz, 2 H), 3.61 (q, J = 5.6 Hz, 1 H), 3.67 (s, 3 H), 5.37–5.44 (m, 1
H), 5.52–5.59 (m, 1 H). 13C NMR (100 MHz, CDCl3): d = 14.365,
22.873, 25.149, 25.969, 27.609, 29.316, 39.362, 29.605, 29.810,
32.079, 34.295, 35.570, 37.058, 51.675, 71.644, 125.341, 133.379,
174.371.
Rinvanil (6)
To a suspension of vanillylamine·HCl (1.21 g, 6.4 mmol) in 2-me-
thyl-2-butanol (130 mL), Et3N (6 mL, 42.7 mmol, 6.67 mol equiv)
was added. The mixture was incubated for 30 min at 37 °C and 250
rpm, and reaction started by addition of MS (1.2 g), methyl ricino-
leate (2 g, 6.4 mmol), and CaLB (1.2 g). The reaction was moni-
tored by TLC (hexane–EtOAc, 85:15). Thereafter, enzyme and MS
were filtered over Celite, a mixture of hexane and EtOAc (1:1, 15
mL) added, and the solid formed was filtered over Celite. The fil-
trate was concentrated under vacuum yielding 3.1 g of raw product,
which after column chromatography (45 g silica gel; 70–230 mesh;
hexane–EtOAc, 7:3) afforded 1.94 g of pure 6 (70.2% yield).
[a]D20 +2.9 (c 1, MeOH). 1H NMR (300 MHz, CDCl3): d = 0.88 (t,
J = 6.9 Hz, 3 H), 1.25–1.35 (m, 16 H), 1.44–1.49 (m, 2 H), 1.63 (q,
J = 6.0 Hz, 2 H), 1.99 (c, J = 6.6 Hz, 2 H), 2.16–2.22 (m, 4 H), 3.56
(q, J = 5.4 Hz, 1 H), 3.85 (s, 3 H), 4.32 (d, J = 5.7 Hz, 2 H), 5.34–
5.43 (m, 1 H), 5.49–5.58 (m, 1 H), 5.91 (br t, J = 5.1 Hz, 1 H), 6.72
(dd, J1 = 7.8 Hz, J2 = 1.8 Hz, 1 H), 6.79 (d, J = 2.1 Hz, 1 H), 6.83
(d, J = 8.1 Hz, 1 H). 13C NMR (75 MHz, CDCl3): d = 14.0, 22.5,
25.6, 27.2, 28.9, 29.01, 29.8, 29.1, 29.2, 29.4, 31.7, 35.2, 36.6, 36.7,
43.4, 55.8, 71.4, 110.7, 114.4, 120.6, 125.2, 130.2, 133.1, 145.0,
146.7, 173.0.
Methyl 12-Phenylacetylricinoleate (9)
In a three-necked round-bottom flask 8 (13.5 g, 43 mmol) and phe-
nylacetic acid (11.66 g, 85.7 mmol) were suspended in CH2Cl2 (150
mL). The reaction mixture was cooled to 0 °C in an ice bath and
DCC (17.6 g, 85.6 mmol) was added. Stirring was continued for 10
min, DMAP (6.3 g, 30 mmol) was added and stirred for an addition-
al 15 min at 0 °C. Thereafter, stirring was continued for 1 h at r.t.
The reaction mixture was then refluxed until the reaction was com-
plete (TLC, hexane–EtOAc, 85:15), filtered over Celite and concen-
trated in a rotatory evaporator. The residue was suspended in
hexane–EtOAc (9:1, 50 mL), vacuum filtered over Celite, and
washed with hexane–EtOAc (9:1, 100 mL); it was then dried over
anhyd Na2SO4 and concentrated in rotatory evaporator (24.68 g of
a crude product). After column chromatography 16.37 g of 9 were
obtained (88.5% yield).
[a]D20 +29.6 (c 1, MeOH). IR (film): 2929, 2856, 1737, 1459, 1437,
1253, 1164, 1023, 722, 700 cm–1. 1H NMR (300 MHz, CDCl3): d =
0.86 (t, J = 6.0 Hz, 3 H), 1.21–1.29 (m, 16 H), 1.50–1.54 (m, 2 H),
1.61 (q, J = 7.2 Hz, 2 H), 1.95 (c, J = 6.6 Hz, 2 H), 2.21–2.32 (m, 4
H), 3.58 (s, 2 H), 3.65 (s, 3 H), 4.87 (q, J = 6.6 Hz, 1 H), 5.22–5.32
(m, 1 H), 5.39–5.48 (m, 1 H), 7.21–7.33 (m, 5 H). 13C NMR (75
MHz, CDCl3): d = 14.0, 22.4, 25.1, 27.2, 29.0, 29.1, 29.4, 31.6,
31.8, 33.5, 34.0, 41.7, 51.3, 74.4, 124.1, 126.8, 128.4, 129.1, 132.5,
134.3, 171.2, 174.2. HRMS–FAB+: m/z calcd for C27H43O4 [M +
H]+: 431.3161; found: 431.3151.
12,4′-Diphenylacetylrinvanil (7)
In a three-necked flask rinvanil (6, 330 mg, 0.76 mmol) and pheny-
lacetic acid (227 mg, 1.67 mmol, 2.2 mol equiv) were disolved in
CH2Cl2 (5 mL). The solution was cooled to 0 °C and then added
DCC (312 mg, 1.52 mmol, 2 mol equiv) and DMAP (92 mg, 0.76
mmol). After stirring for 20 min at 0 °C and 2 h at r.t. (TLC; hex-
ane–EtOAc, 1:1), the reaction mixture was filtered over Celite and
washed with CH2Cl2. The amount of 550 mg of concentrated raw
product yielded 390 mg of 7 (76.5% yield, yellow oil) after column
chromatography (hexane–EtOAc, 7:3).
Acknowledgment
1H NMR (300 MHz, CDCl3): d = 0.86 (t, J = 7.1 Hz, 3 H), 1.21–
1.28 (m, 16 H), 1.50–1.52 (m, 2 H), 1.63 (q, J = 6.2 Hz, 2 H), 1.96
(c, J = 7.4 Hz, 2 H), 2.16 (t, J = 7.7 Hz, 2 H), 2.21–2.35 (m, 2 H),
The authors acknowledge DGAPA-UNAM for Ignacio Regla sab-
batical fellowship at IBT-UNAM and for grant PAPIIT-IN226706-
3. Authors are also grateful to Ma de los Angeles Peña, Javier Pérez-
Synlett 2008, No. 18, 2869–2873 © Thieme Stuttgart · New York

LETTER
Chemoenzymatic Synthesis of Phenylacetylrinvanil
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Flores J., and Rocío Patiño-Maya from Instituto de Química,
UNAM for spectroscopic analysis, to Fernando González and Mi-
guel Angel Xolocotzi for analytical support, and to Novozymes-
México for the generous gift of CaLB.
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(17) 1H and 13C NMR spectroscopy was carried out on a JEOL
Eclipse instrument at 300 and 400 MHz (1H NMR operating
frequency), with TMS as an internal standard and CDCl3 as
solvent. The IR spectra were carried out on a Bruker
spectrophotometer Tensor 27. The [a]D20 values were
determined on a 341 Perkin Elmer polarimeter, at 1 dm cell
length. HRMS was determined on a JEOL JMS-SX102A
instrument. Silica gel chromatography: 70–230 mesh.
Multiplicity keys: s = singlet, d = doublet, t = triplet, c =
quartet, q = quintet, m = multiplet, br = broad, dd = doublet
of doublets.
Synlett 2008, No. 18, 2869–2873 © Thieme Stuttgart · New York

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