5700
N. M. Carballeira et al. / Tetrahedron Letters 50 (2009) 5699–5700
Table 1
i-ii
iii
OTHP
OH
OTHP
O
Antifungal activity (MIC values, lM) against Candida albicans (SDB) and Cryptococcus
neoformans (SDB) at 35–37 °C after 24–48 ha
OH
Compound
C. albicans
ATCC 60193
C. neoformans
ATCC 66031
2
3
4
( )-4-Methoxydecanoic
acid (1)
Decanoic acid
Fluconazole
Amphotericin B
DMSO
1457
1457
CO2H
OTHP
iv
v-vi
25,478
>500
<0.3
25,478
<0.9
<0.3
OCH3
OCH3
5
1
>5000
>5000
Scheme 1. Reagents and conditions: (i) DHP/PTSA,CHCl3, rt, 5 h, 88%; (ii) MMPP/
EtOH, 48 h, 89%; (iii) CH3(CH2)3CH2MgBr, Cu(I)/THF, ꢀ78 °C to ꢀ30 °C, 81%; (iv)
NaH/CH3I, THF, 0 °C to rt, 2 h, 88%; (v) PTSA, CHCl3, 45 °C, 2 h, 73%; (vi) PDC/DMF,
24 h, 63%.
a
The results are the average of three separate experiments. The upper limit of the
standard error of the mean (SEM) was 10%.
that C-4 methoxylation increased the antifungal activity of the par-
ent n-decanoic acid. In fact, for n-decanoic acid C-4 methoxy sub-
stitution seems to be more effective than C-2 methoxy substitution
in increasing the antifungal activity of n-decanoic acid.6
the 4,5-epoxy-1-[(tetrahydropyran-2-yl)oxy]pentane (3) in 89%
yield after purification of the crude product using silica gel column
chromatography (60–200 mesh) and eluting with hexane/diethyl
ether (8:2). MMPP turned out to be more efficient than the classical
m-chloroperoxybenzoic acid (m-CPBA) in epoxidizing these al-
kenes, since the latter reagent only afforded moderate to low yields
even after long reaction times. The THP-protected epoxide 3 was
then opened with 1-pentylmagnesium bromide assisted by
catalytic amounts of copper(I) chloride in THF at a reaction tem-
perature range of ꢀ78 °C to ꢀ30 °C, which afforded the desired
4-hydroxy-1-[(tetrahydropyran-2-yl)oxy]decane (4) in an 81%
yield after silica gel (60–200 mesh) column chromatographic puri-
fication. The free hydroxyl group in 4 was then readily methylated
with methyl iodide in the presence of sodium hydride in THF,
which afforded the 4-methoxy-1-[(tetrahydropyran-2-yl)oxy]dec-
ane (5) in an 88% yield. Deprotection of the primary alcohol was
effectively accomplished with PTSA in CHCl3 at 45 °C for 2 h, which
afforded the ( )-4-methoxydecan-1-ol in a 73% yield (Scheme 1).
Final oxidation to the acid was accomplished by reaction of the
alcohol with pyridinium dichromate (PDC) in DMF for 24 h, which
resulted in a 63% yield of 1.9 The overall yield for this six-step syn-
thesis was 25%.
As to the reasons for the better antifungal activity of 1 over that
of n-decanoic acid we can only speculate at this stage and more
mechanistic studies are required. The addition of the C-4 methoxy
functionality possibly makes the fatty acid more soluble than
unsubstituted n-decanoic acid thus facilitating its interaction with
the target sites. In addition, based on the previously published
antifungal mechanism of decanoic acid8 we can also speculate that
acid 1 seems to be able to more efficiently disrupt the fungal mem-
branes due to the mid-chain methoxy substitution. Moreover, the
title compound 1 may also inhibit fatty acid biosynthesis within
the fungi interacting with some key enzymes. In summary, our re-
sults clearly demonstrate that mid-chain methoxylated fatty acids
are valuable compounds that can be optimized for developing
more potent antifungal agents and thus merit further scrutiny in
the search for better antifungal analogs.
Acknowledgments
The project described was supported by Award Number
SC1GM084708 from the National Institutes of General Medical Sci-
ences. We also acknowledge the financial supports from National
Science Foundation, Grant Number CHE 0748555, and American
Cancer Society grant number RSG-07-290-01-CDD. We thank Dr.
Fred Strobel (Emory University) for the high resolution mass spec-
tral data.
The most significant absorption in the NMR spectrum of 1 was
observed for the carbons and hydrogens bearing the methoxy func-
tionality. For example, the methoxy protons resonated at
d
3.32 ppm and the methoxy carbon was observed at d 56.5 ppm,
while the methine hydrogen (CHOCH3) resonated at d 3.20 ppm
and the methine carbon (CHOCH3) at d 79.9 ppm. These 1H NMR
and 13C NMR displacements seem to be characteristic for saturated
mid-chain methoxylated fatty acids and useful as a future refer-
ence for other similar analogs. It is also interesting to mention that
in the 70 eV electron impact (EI) mass spectrum of 1 the typical
McLafferty rearrangement of fatty acids at m/z = 60 was greatly re-
duced (1% relative abundance) by the presence of the methoxy
References and notes
1. Feron, Y.; Dufosse, L.; Pierard, E.; Bonnarme, P.; Le Quere, J.-L.; Spinnler, H.-E.
Appl. Environ. Microbiol. 1996, 62, 2826.
2. Greger, V.; Schieberle, P. J. Agric. Food Chem. 2007, 55, 5221.
3. Lozano, P. R.; Miracle, E. R.; Krause, A. J.; Drake, M.; Cadwallader, K. R. J. Agric.
Food Chem. 2007, 55, 7840.
4. Carmines, E. L. Food Chem. Toxicol. 2002, 40, 77.
5. Sjögren, J.; Magnusson, J.; Broberg, A.; Schnürer, J.; Kenne, L. Appl. Environ.
Microbiol. 2003, 69, 7554.
6. Carballeira, N. M.; Ortiz, D.; Parang, K.; Sardari, S. Arch. Pharm. Pharm. Med. Chem.
2004, 337, 152.
7. Carballeira, N. M.; O’Neill, R.; Parang, K. Chem. Phys. Lipids 2007, 150, 82.
8. Bergsson, G.; Arnfinnsson, J.; Steingrímsson, Ó.; Thormar, H. Antimicrob. Agents
Chemother. 2001, 45, 3209.
functionality at C-4. In the mass spectrum of 1 the a-fragmentation
at both sides of the methoxylated carbon predominated, but the
fragments containing the carboxyl end (at m/z = 117 corresponding
þ
to C5H9O3 and at m/z = 85 corresponding to C4H5O2þ) were the
most abundant.
The antifungal activity of 1 was determined against a fluconaz-
ole-resistant strain of C. albicans (ATCC 60193) and against C. neo-
formans (ATCC 66031) following our previously published protocol
(Table 1).6,7 n-Decanoic acid was also tested as a control. As can be
seen from the data given in Table 1 the ( )-4-methoxydecanoic
acid (1) was approximately 17-fold more antifungal against both
9. Spectral data for the ( )-4-methoxydecanoic acid (1): Transparent oil; IR (neat):
m
max 3500–2500, 2928, 1712, 1462, 1377, 1282, 1096, 936 cmꢀ1 1H NMR (CDCl3,
;
300 MHz): d 3.32 (s, 3H, –OCH3), 3.20 (m, 1H, H-4), 2.43 (t, J = 7.5 Hz, 2H, H-2),
1.97–1.67 (m, 2H, H-3), 1.52 (m, 2H, H-5), 1.27 (m, 8H, –CH2–), 0.87 (t, J = 6.7 Hz,
3H, –CH3); 13C NMR (CDCl3, 75.5 MHz): d 179.6, 79.9, 56.5, 33.1, 31.8, 29.9, 29.4,
28.2, 25.1, 22.6, 14.0; GC–MS (70 eV) m/z (rel. intensity) 201(M+ꢀ1, 0.1), 187(2),
170(1), 169(2), 129(18), 116(54), 97(16), 85(100), 71(14), 60(1), 57(7), 55(24);
HRMS (APCI): calcd for C11H23O3 (M+H)+ 203.1642, found: 203.1639.
fungal strains (MIC = 1457
lM) when compared to n-decanoic acid
(MIC = 25,478 M). Therefore, the antifungal results clearly show
l