Facile total synthesis and antimicrobial activity of the marine fatty acids (Z)-2-methoxy-5-hexadecenoic acid and (Z)-2-methoxy-6-hexadecenoic acid

Article abstract of DOI:10.1021/np980274o

The total synthesis of the naturally occurring (Z)-2-methoxy-5- hexadecenoic acid and (Z)-2-methoxy-6-hexadecenoic acid was accomplished using as a key step Mukaiyama's trimethylsilyl cyanide addition to 4- and 5- pentadecenal, respectively. These syntheses further confirm the structures of the natural marine fatty acids and corroborate their cis double-bond stereochemistry. The title compounds were antimicrobial against the Gram- positive bacteria Staphylococcus aureus (MIC 0.35 μmol/mL) and Streptococcus faecalis (MIC 0.35 μmol/mL).

Full text of DOI:10.1021/np980274o

J . Nat. Prod. 1998, 61, 1543-1546
1543
F a cile Tota l Syn th esis a n d An tim icr obia l Activity of th e Ma r in e F a tty Acid s
(Z)-2-Meth oxy-5-h exa d ecen oic Acid a n d (Z)-2-Meth oxy-6-h exa d ecen oic Acid
Ne´stor M. Carballeira,* Anastacio Emiliano, Norali Herna´ndez-Alonso, and Fernando A. Gonza´lez
Department of Chemistry, University of Puerto Rico, P. O. Box 23346, San J uan, Puerto Rico 00931
Received J une 24, 1998
The total synthesis of the naturally occurring (Z)-2-methoxy-5-hexadecenoic acid and (Z)-2-methoxy-6-
hexadecenoic acid was accomplished using as a key step Mukaiyama’s trimethylsilyl cyanide addition to
4- and 5-pentadecenal, respectively. These syntheses further confirm the structures of the natural marine
fatty acids and corroborate their cis double-bond stereochemistry. The title compounds were antimicrobial
against the Gram-positive bacteria Staphylococcus aureus (MIC 0.35 µmol/mL) and Streptococcus faecalis
(MIC 0.35 µmol/mL).
Naturally occurring R-methoxy fatty acids are rare and
have only been reported from the phospholipids of
sponges.1-3 Some examples include normal-chain satu-
rated 2-methoxy fatty acids of between 16 and 24 carbons,
and very long-chain monounsaturated fatty acids, such as
(2R,21Z)-2-methoxy-21-octacosenoic acid, which was the
first naturally occurring R-methoxy fatty acid reported from
a phospholipid.2 Some time ago, we identified (Z)-2-
methoxy-5-hexadecenoic acid (5) and (Z)-2-methoxy-6-
hexadecenoic acid (9) from the phospholipids of several
Caribbean sponges, and recently, we identified the 2-meth-
oxyhexadecanoic acid as a plausible biosynthetic precursor
for these R-methoxylated hexadecenoic acids.3,4 Despite
most of these identification efforts, complete characteriza-
tion of the R-methoxylated hexadecenoic acids 5 and 9 is
still lacking. Moreover, these R-methoxylated fatty acids
were identified, in trace amounts and in complex mixtures,
by GC-MS, and no material is thus available for further
biological screening.3 Other middle-chain methoxy-branched
fatty acids, such as (4E,7S)-7-methoxy-4-tetradecenoic acid,
isolated from Lyngbya majuscula, display antimicrobial
activity against Gram-positive bacteria such as Staphylo-
coccus aureus.5 Therefore, it became of interest to us to
develop an efficient synthesis for these R-methoxylated
fatty acids and to test their antimicrobial activity. In this
paper we describe the synthesis of (Z)-2-methoxy-5-hexa-
decenoic acid (5) and (Z)-2-methoxy-6-hexadecenoic acid (9),
using as a key synthetic step Mukaiyama’s trimethylsilyl
cyanide addition to aldehydes under basic conditions.6 We
further confirm the cis double-bond stereochemistry of the
naturally occurring compounds by coelution of the synthetic
methyl esters with the methyl esters of the natural acids.
We also report the antimicrobial activity of these R-meth-
oxy fatty acids.
1,3-dioxolane in an 83% isolated yield. No double-bond
isomerization was observed. The dioxolane was removed
with 5% HCl in acetone-water (1:1), and the equilibrium
favored the already-reported (Z)-4-pentadecenal.7,8 Addi-
tion of trimethylsilyl cyanide to (Z)-4-pentadecenal, under
triethylamine catalysis as described by Mukaiyama for
other shorter-chain analogues, resulted in a 95% isolated
yield of 2-trimethylsilyloxy-5-hexadecenonitrile.6 Under
basic conditions the trimethylsilyloxynitrile easily reverts
to the original aldehyde. So, the trimethylsilyloxynitrile
was first transformed into the corresponding R-hydroxy
amide under concentrated acid conditions (HCl), and this
was then hydrolyzed to the R-hydroxy acid with 50%
NaOH. Under these conditions the intermediate (Z)-2-
hydroxy-5-hexadecenoic acid was obtained in a 70% yield.
Double methylation was then successfully accomplished
with NaH and methyl iodide in DMSO resulting in the
already-reported methyl (Z)-2-methoxy-5-hexadecenoate,
which coeluted in capillary GC with an authentic sample
from Amphimedon compressa.4 This experiment confirmed
the cis double-bond stereochemistry for this acid and
verifies the structure by total synthesis. Final saponifica-
tion with KOH in ethanol afforded the desired (Z)-2-
methoxy-5-hexadecenoic acid (5). This is the first total
synthesis for 5; the overall yield was 12%.
The synthesis of (Z)-2-methoxy-6-hexadecenoic acid (9)
first required the preparation of (Z)-5-pentadecenal as the
key intermediate (Scheme 2). In this case, commercially
available decyl aldehyde was coupled with 4-carboxybu-
tyltriphenylphosphonium bromide, under Wittig conditions,
resulting in a 10:1 mixture of the known (Z)- and (E)-5-
pentadecenoic acids.9,10 The acids were then reduced to
the desired (Z)-5-pentadecenal via (Z)-5-pentadecen-1-ol,
a known pheromone.11-13 Addition of trimethylsilyl cya-
nide to (Z)-5-pentadecenal, also under triethylamine ca-
talysis, yielded 2-trimethylsilyloxy-6-hexadecenonitrile in
a 95% isolated yield. The trimethylsilyl cyanide was also
transformed into the intermediate R-hydroxy amide with
concentrated HCl, and then hydrolyzed to (Z)-2-hydroxy-
6-hexadecenoic acid with 50% NaOH. Double methylation
was also successfully accomplished with NaH and methyl
iodide, in DMSO, resulting in methyl (Z)-2-methoxy-6-
hexadecenoate, which has only been identified in the
sponge Spheciospongia cuspidifera.3 Final saponification
with KOH in ethanol afforded the desired (Z)-2-meth-
oxy-6-hexadecenoic acid (9) in an overall 3% yield. It
is of interest to mention that a different synthesis for
Resu lts a n d Discu ssion
The synthesis of (Z)-2-methoxy-5-hexadecenoic acid (5)
first required the preparation of (Z)-4-pentadecenal.7,8 This
was accomplished starting with commercially available
1-dodecyne, which was coupled with 2-(2-bromoethyl)-1,3-
dioxolane and n-BuLi in tetrahydrofuran-hexamethylphos-
phoramide, resulting in a 68% yield of 2-(3-tetradecyne)-
1,3-dioxolane (Scheme 1). Subsequent catalytic hydrogena-
tion, using Lindlar’s catalyst, afforded 2-(3-tetradecenyl)-
* To whom correspondence should be addressed. Tel.: (787) 764-0000
ext. 4791. Fax: (787) 751-0625. E-mail: ncarball@upracd.upr.clu.edu.
10.1021/np980274o CCC: $15.00
© 1998 American Chemical Society and American Society of Pharmacognosy
Published on Web 10/17/1998

1544 J ournal of Natural Products, 1998, Vol. 61, No. 12
Carballeira et al.
Sch em e 1a
a
Key: (i) n-BuLi, THF-HMPA, -70 °C; (ii) H2, Lindlar; (iii) 5% HCl, Me2CO-H2O, 60 °C; (iv) TMS-CN, Et3N, CH2Cl2, -10 °C; (v) HCl concd room
temperature; (vi) 50% NaOH, heat; (vii) NaH/DMSO, CH3I; (viii) KOH-EtOH.
Sch em e 2a
a
Key: (i) HO2C(CH2)3CH2PPh3+Br-, n-BuLi, THF/DMSO (1:1), -10 °C; (ii) 1 N HCl-MeOH, 3 h; (iii) LiAlH4-THF, -78 °C; (iv) PCC (1.5 equiv), CH2Cl2,
room temperature; (v) TMS-CN, Et3N, CH2Cl2, -10 °C, 2 h; (vi) HCl concd, room temperature; (vii) 50% NaOH, heat; (viii) NaH/DMSO, CH3I; (ix) KOH-
EtOH.
Ta ble 1. Antimicrobial Activity of 5 and 9
MIC (µmol/mL)
2-methoxyhexadecanoic acid was not antimicrobial against
any of these four microorganisms (MIC >100 µg/mL).4
We have presented here a facile synthetic approach to
R-methoxylated fatty acids. Isomers 5 and 9 showed
similar antimicrobial activity against Gram-positive bac-
teria and no activity against Gram-negative bacteria.
bacteria
5
9
S. aureus
S. faecalis
P. aeruginosaa
E. colia
0.35
0.35
0.35
0.35
Exp er im en ta l Section
a
Not active (MIC > 200 µg/mL).
Gen er a l Exp er im en ta l P r oced u r es. IR spectra were
recorded on a Nicolet 600 FT-IR spectrophotometer. 1H and
13C NMR were recorded on a General Electric QE-300 or
Bruker DPX-300 spectrometers. 1H NMR chemical shifts are
reported with respect to internal Me4Si, and 13C NMR chemical
shifts are reported in parts per million relative to CDCl3 (77.0
ppm). GC-MS analyses were recorded at 70 eV using a
Hewlett-Packard 5972A MS ChemStation equipped with a
30 m × 0.25 mm special performance capillary column (HP-
5MS) of polymethyl siloxane cross-linked with 5% phenyl
methylpolysiloxane. HRMS data was obtained in a VG Au-
toSpec high-resolution mass spectrometer.
methyl (Z)-2-methoxy-6-hexadecenoate was recently re-
ported, and the key step was the addition of tris(meth-
ylthio)methyllithium to (Z)-5-pentadecenal followed by
methylation (NaH, MeI) and hydrolysis (HgCl2, HgO,
MeOH-H2O).14 However, acid 9 was not synthesized in
the latter report.
Both (Z)-2-methoxy-5-hexadecenoic acid (5) and (Z)-2-
methoxy-6-hexadecenoic acid (9) displayed moderate and
similar antimicrobial activity against the Gram-positive
bacteria Staphylococcus aureus (MIC 0.35 µmol/mL) and
Streptococcus faecalis (MIC 0.35 µmol/mL) (Table 1). They
were not, however, active against the Gram-negative
bacteria Pseudomonas aeruginosa and Escherichia coli. The
2-(3-Tetr a d ecyn yl)-1,3-d ioxola n e (1). Into a 250-mL two-
necked round-bottom flask, equipped with a magnetic stirrer,
was placed 1-dodecyne (4.6 g, 27 mmol) in 50 mL of anhydrous

Synthesis and Activity of Marine Fatty Acids
J ournal of Natural Products, 1998, Vol. 61, No. 12 1545
THF. The reaction temperature was lowered to -78 °C, and
27 mL (54 mmol) of 2.0 M n-butyllithium in hexane was added.
After 0.5 h HMPA (12.5 mL) was added at -50 °C, followed
by the addition of 5.0 g (27.6 mmol) of 2-(2-bromoethyl)-1,3-
dioxolane in THF. Stirring was continued for 8 h at this
temperature, and the reaction mixture was finally quenched
with a saturated NH4Cl solution (20 mL). Purification by Si
gel column chromatography using hexane-ether 1:1 (v/v) as
eluent, furnished 5.0 g (68% yield) of the tetradecynedioxo-
(13), 109 (8), 101 (36), 96(29), 84 (24), 81 (38), 75 (46), 73 [C3H9-
Si+] (100), 69 (31), 67 (56), 57 (39), 55 (67); HREIMS m/z
323.2653 (calcd for C19H37NOSi, 323.2644).
2-Hydr oxy-5(Z)-h exadecen oic acid. Into a 100-mL round-
bottom flask equipped with a magnetic stirrer was placed
trimethylsilyloxyhexadecenonitrile (0.59 g, 1.8 mmol) in 10 mL
of THF. Concentrated HCl (5 mL) was added, and the reaction
mixture was heated at 65 °C for 24 h. The reaction mixture
was then cooled (ice bath) and made alkaline by the slow
addition of 10 mL of 50% NaOH. The reaction mixture was
steam-distilled until no more NH3 passed into the distillate,
H2O (25 mL) was then added, followed by extraction with ether
(3 × 15 mL). After drying over Na2SO4, the ether was suction-
filtered and evaporated in vacuo, affording 0.3 g (70% yield)
of the acid, which was used for the next step without further
purification: 1H NMR (CDCl3, 300 MHz) δ 5.37 (2H, m, H-5,
H-6), 4.24 (1H, m, H-2), 2.35 (2H, m), 2.16 (2H, m), 2.02 (2H,
br t, J ) 6.5 Hz, H-7), 1.26 (16H, br s, -CH2-), 0.87 (3H, t, J
) 7.0 Hz, CH3); 13C NMR (CDCl3, 75 MHz) δ 178.7 (s, C-1),
131.6 (d), 127.7 (d), 70.2 (d, C-2), 34.1 (t, C-7), 31.9 (t), 29.62
(t), 29.56 (t), 29.53 (t), 29.3 (t), 29.2 (t), 27.2 (t), 26.7 (t), 24.9
(t), 22.6 (t), 14.0 (q, CH3).
Meth yl 2-m eth oxy-5(Z)-h exa d ecen oa te. Into a two-
necked round-bottom flask, equipped with a magnetic stirrer
and under nitrogen, was placed (Z)-2-hydroxy-5-hexadecenoic
acid (0.25 g, 0.9 mmol) dissolved in 5 mL of anhydrous DMSO.
Two equivalents of NaH, dissolved in 1.0 mL anhydrous
DMSO, were added, and the reaction mixture was stirred for
10 min. Subsequently, an excess of MeI (4 equivalents) was
slowly added, and the reaction mixture was stirred for an
additional 20 min. The reaction mixture was finally extracted
with hexane (3 × 10 mL), dried over MgSO4, and concentrated
in vacuo, affording 0.15 g (54% yield) of the methoxylated
methyl ester:3 1H NMR (CDCl3, 300 MHz) δ 5.35 (2H, m, H-5,
H-6), 3.75 (1H, t, J ) 6.5 Hz, H-2), 3.74 (3H, s, -CO2CH3),
3.37 (3H, s, -OCH3), 2.12 (2H, m), 2.0 (2H, m, H-7), 1.75 (2H,
q, J ) 7 Hz), 1.25 (16H, br s, -CH2-), 0.87 (3H, t, J ) 6.8 Hz,
CH3); 13C NMR (CDCl3, 75 MHz) δ 173.3 (s, C-1), 131.4 (d),
127.8 (d), 79.8 (d, C-2), 58.1 (q, -OCH3), 51.8 (q, -CO2CH3),
33.2 (t), 31.9 (t), 29.65 (t), 29.60 (t), 29.55 (t), 29.52 (t), 29.3
(t), 27.2 (t), 22.8 (t), 22.6, (t), 14.0 (q, C-16); GC-MS (70 eV)
m/z 298 [M+] (1), 266 (3), 239 (5), 207 (2), 192 (1), 180 (1), 150
(2), 140 (2), 136 (2), 125 (2), 111 (6), 109 (4), 105 (5), 104 (100),
97 (12), 96 (4), 95 (11), 93 (5), 89 (9), 87 (4), 83 (10), 81 (15), 79
(11), 75 (5), 69 (15), 67 (22), 57 (14), 55 (32).
lane: IR (neat) νmax 2956, 2924, 2852, 1457, 1142, 1040 cm-1
;
1H NMR (CDCl3, 300 MHz) δ 4.87 (1H, t, J 1,2 ) 4.8 Hz, H-1),
3.84 (2H, AA′BB′, -OCH2-), 3.74 (2H, AA′BB′, -OCH2-), 2.18
(2H, tt, J 3,2 ) 7.4 Hz and J 3,6 ) 2.3 Hz, H-3), 2.02 (2H, tt, J 6,7
) 6.7 Hz and J 6,3 ) 2.3 Hz, H-6), 1.73 (2H, dt, J 2,3 ) 7.4 Hz
and J 2,1 ) 4.8 Hz, H-2), 1.18 (16H, br s, CH2), 0.79 (3H, t, J )
6.5 Hz, -CH3); 13C NMR (CDCl3, 75 MHz) δ 103.2 (d, C-1),
80.2 (s, C-4), 78.7 (s, C-5), 64.6 (t, -OCH2-), 33.3 (t, C-2),
31.7 (t, C-13), 29.4 (t), 29.1 (t), 29.0 (t), 28.9 (t), 28.7 (t), 22.5
(t), 18.5 (t, C-6), 13.8 (q, CH3), 13.5 (t, C-3); GC-MS (70 eV)
m/z 266 [M+] (1), 238 (1), 237 (7), 195 (1), 167 (3), 153 (4),
140 (2), 139 (16), 125 (4), 113 (1), 99 (4), 97 (1), 95 (5), 93
(2), 92 (1), 91 (3), 87 (3), 86 (18), 81 (5), 80 (2), 79 (7), 77 (4),
74 (4), 73 [C3H5O2+] (100), 68 (2), 67 (9), 65 (4), 57 (3), 55
(10); HREIMS m/z 265.2168 [M+ - H] (calcd for C17H29O2,
265.2167).
2-(3-Tetr adecen yl)-1,3-dioxolan e (2). Into a 50-mL round-
bottom flask, equipped with a magnetic stirrer and 40 mL of
dry hexane were placed 2.7 g (10 mmol) of 2-(3-tetradecynyl)-
1,3-dioxolane, 0.2 equivalents of quinoline, and 1.5 g of
Lindlar’s catalyst. After a couple of purging cycles, hydrogen
was added until a volume equivalent to the initial amount of
alkyne was consumed. After filtration and removal of the
solvent in vacuo, 2.2 g (83% yield) of the alkene 2 was
obtained: IR (neat) νmax 3006, 2957, 2929, 2855, 1466, 1407,
1141, 1040, 724 cm-1; 1H NMR (CDCl3, 300 MHz) δ 5.37 (2H,
m, H-4, H-5), 4.85 (1H, t, J ) 4.8 Hz, H-1), 3.97 (2H, AA′BB′,
-OCH2-), 3.84 (2H, AA′BB′, -OCH2-), 2.15 (2H, m, H-3), 2.03
(2H, m, H-6), 1.70 (2H, m, H-2), 1.25 (16H, br s, -CH2-), 0.87
(3H, t, J ) 6.8 Hz, -CH3); 13C NMR (CDCl3, 75 MHz) δ 130.7
(d, C-4), 128.4 (d, C-5), 104.2 (d, C-1), 64.8 (t, -OCH2-), 33.9
(t, C-2), 31.9 (t), 29.7 (t), 29.6 (t), 29.5 (t), 29.3 (t), 29.28 (t),
27.1 (t, C-6), 22.7 (t), 21.9 (t, C-3), 14.1 (q, C-15); GC-MS (70
eV) m/z 268 [M+] (6), 239 (4), 225 (11), 211 (4), 206 (1), 197
(3), 183 (3), 169 (4), 156 (2), 155 (16), 141 (14), 127 (7), 113
(4), 100 (9), 99 [C5H7O2+] (96), 95 (3), 87 (4), 86 (25), 83 (7), 81
(5), 80 (6), 79 (4), 74 (3), 73 [C3H5O2+] (100), 69 (6), 67 (10), 57
2-Meth oxy-5(Z)-h exa d ecen oic a cid (5). Into a 25-mL
round-bottom flask was placed methyl (Z)-2-methoxy-5-hexa-
decenoate (0.050 g, 0.17 mmol) in 10 mL of 1.0 M KOH in
EtOH. The reaction mixture was refluxed for 1 h and then
allowed to cool to room temperature. The EtOH was evapo-
raed in vacuo and the resulting salt washed with 5 mL of
hexane to extract the nonsaponifiable matter, which was
discarded. The salt was then dissolved in 15 mL of H2O and
acidified with 6.0 M HCl followed by extraction (3 × 10 mL)
with ethyl ether. The organic extracts were put together and
the organic solvent evaporated in vacuo, obtaining 0.033 g of
5 for a 66% yield:3 IR (neat) νmax 3600-3100, 3009, 2961, 2931,
2855, 1714, 1457, 1206, 1124, 734 cm-1; 1H NMR (CDCl3, 300
MHz) δ 5.45-5.30 (2H, m, H-5,6), 3.78 (1H, br t, J ) 6.1 Hz,
H-2), 3.43 (3H, s, -OCH3), 2.36 (2H, m), 2.14 (2H, m), 2.0 (2H,
m, H-7), 1.81 (2H, m, H-3), 1.25 (14H, br s, -CH2-), 0.87 (3H,
t, J ) 6.7 Hz, CH3); 13C NMR (CDCl3, 75 MHz) δ 175.8 (s, C-1),
131.9 (d), 127.9 (d), 79.8 (d, C-2), 58.6 (q, -OCH3), 32.7 (t),
32.2 (t), 30.0 (t), 29.98 (t), 29.94 (t), 29.91 (t), 29.68 (t), 27.6
(t), 23.0 (t), 14.4 (q, CH3); EIMS (70 eV) m/z 284 [M+] (0.6),
266 [M+ - H2O] (0.9), 252 [M+ - CH3OH] (2.8), 239 (7.3), 207
(2.1), 180 (4.2), 129 (8.5), 111 (10), 109 (15.7), 91 (6.6), 90 (100),
71 (19), 69 (50.7), 68 (15.8), 67 (37.5), 57 (5), 55 (63); HREIMS
m/z 284.2332 (calcd for C17H32O3, 284.2351).
(5), 55 (14); HREIMS m/z 268.2408 (calcd for
268.2402).
C17H32O2,
(Z)-4-P en ta d ecen a l (3). Into a 25-mL round-bottom flask,
equipped with a magnetic stirrer, were placed 2.0 g (7.5 mmol)
of 2-(3-tetradecenyl)-1,3-dioxolane in 15 mL of 5% HCl in 1:1
Me2CO-H2O. The reaction mixture was stirred overnight at
60 °C and extracted with ether (2 × 15 mL), dried over MgSO4,
filtered, and the ether removed in vacuo affording 1.8 g (90%
yield) of the previously reported (Z)-4-pentadecenal.7,8
2-Tr im eth ylsilyloxy-5(Z)-h exa d ecen on itr ile (4). To an
anhydrous CH2Cl2 solution (5 mL) of trimethylsilyl cyanide
(0.2 g, 2 mmol) and 4-pentadecenal (0.45 g, 2 mmol), catalytic
amounts of Et3N (10 mol %) were added at -10 °C. The
reaction mixture was stirred for 2 h at this temperature, and
the solvent removed in vacuo, affording 0.61 g (1.9 mmol) of
product for a 95% yield: IR (neat) νmax 3013, 2955, 2926, 2855,
1471, 1458, 1255, 1114, 846 cm-1; 1H NMR (CDCl3, 300 MHz)
δ 5.30 (1H, m, H-5), 5.42 (1H, m, H-6), 4.38 (1H, t, J ) 6.5 Hz,
H-2), 2.19 (2H, br q, J ) 7.0 Hz, H-4), 2.1 (2H, br q, J ) 6.5
Hz, H-7), 1.81 (2H, br q, J ) 7.0 Hz, H-3), 1.25 (16H, br s,
-CH2-), 0.86 (3H, t, J ) 7.0 Hz, -CH3), 0.20 (9H, s,
-Si(Me3); 13C NMR (CDCl3, 75 MHz) δ 132.1 (d, C-5), 126.7
(d, C-6), 119.9 (d, C-1), 60.8 (2H, d, C-2), 36.2 (t, C-4), 31.9 (t),
29.6 (t), 27.2 (t, C-7), 22.6 (t), 22.5 (t, C-3), 14.0 (q, CH3), -0.45
(q, -SiMe3); GC-MS (70 eV) m/z 323 [M+] (9), 308 (16), 281
(3), 280 (3), 265 (1), 218 (4), 210 (4), 204 (7), 192 (4), 190 (7),
184 (4), 180 (4), 176 (9), 169 (13), 168 [C8H14NOSi+] (43), 162
(10), 155 (11) 152 (7), 150 (6), 148 (11), 144 (10), 135 (11), 134
(14), 129 (17), 128 [C5H10NOSi+] (16), 121 (11), 120 (16), 116
(Z)-5-P en t a d ecen oic a cid (6): obtained as a 10:1 mix-
ture (38% yield) of (Z)-5-pentadecenoic acid and (E)-5-penta-
decenoic acid in the reaction of 4-carboxybutyltriphenylphos-
phonium bromide and decyl aldehyde with 2.0 M n-BuLi in
dimethyl sulfoxide-tetrahydrofuran (1:1) as previously de-
scribed.9,10

1546 J ournal of Natural Products, 1998, Vol. 61, No. 12
Carballeira et al.
Met h yl (Z)-5-p en t a d ecen oa t e: obtained in a 95% yield
from the reaction of (Z)-5-pentadecenoic acid and 1M HCl in
MeOH following the standard literature procedure.11
(Z)-5-P en ta d ecen -1-ol: prepared in a 70% yield by reacting
methyl (Z)-5-pentadecenoate with LiAlH4 in dry THF as
previously described.12
(Z)-5-P en ta d ecen a l (7): obtained in a 60% yield by react-
ing (Z)-5-pentadecen-1-ol with pyridinium chlorochromate in
dry CH2Cl2 using literature standard procedures.13
2-Tr im eth ylsilyloxy-6(Z)-h exa d ecen on itr ile (8). To an
anhydrous CH2Cl2 solution (5 mL) of trimethylsilyl cyanide
(0.2 g, 2 mmol) and 5-pentadecenal (0.45 g, 2 mmol), catalytic
amounts of Et3N (10 mol %) were added at -10 °C. The
reaction mixture was stirred for 2 h at the same temperature
and the solvent removed in vacuo, affording 0.61 g (1.9 mmol)
of product for a 94% yield: 1H NMR (CDCl3, 300 MHz) δ 5.39-
5.26 (2H, m), 4.36 (1H, t, J ) 6.6 Hz, H-2), 2.20 (2H, m), 1.99
(2H, m), 1.69 (2H, m), 1.25 (16 H, br s, -CH2-), 0.86 (3H, t, J
) 6.9 Hz, -CH3), 0.20 (9H,s, -SiMe3); 13C NMR (CDCl3, 75
MHz) δ 130.9 (d), 128.2 (d), 119.7 (d, C-1), 61.2 (2H, d, C-2),
35.6 (t), 31.6 (t), 29.5 (t), 29.2 (t), 26.5 (t), 22.5 (t), 13.9 (q, C-16),
-0.58 (q, -SiMe3); GC-MS (70 eV) m/z 323 [M+] (8), 309 (7),
308 (28), 281 (7), 266 (4), 225 (5), 214 (3), 210 (11), 206 (6),
192 (6), 182 (5), 169 (9), 168 (9), 166 (5), 156 (6), 155 (9), 154
(5), 140 (7), 135 (20), 129 (34), 128 (6), 121 (11), 120 (28), 113
(9), 101 (14), 97 (8), 96 (13), 95 (17), 94 (8), 93 (14), 84 (22), 83
(15), 82 (19), 81 (24), 80 (10), 79 (21), 75 (48), 74 (11), 73 (100),
69 (26), 68 (20), 67 (39), 59 (17), 57 (26), 56 (15), 55 (56), 54
(33).
84 (13), 83 (33), 82 (30), 81 (66), 80 (19), 79 (39), 77 (11), 75
(14), 71 (77), 70 (11), 69 (54), 68 (38), 67 (94), 59 (29), 58 (24),
57 (49), 56 (19), 55 (100), 54 (49). Anal. C, 72.21%; H, 11.49%;
calcd for C18H34O3: C, 72.44; H, 11.48.
2-Meth oxy-6(Z)-h exa d ecen oic a cid (9). Into a 25-mL
round-bottom flask was placed methyl (Z)-2-methoxy-6-hexa-
decenoate (0.040 g, 0.13 mmol) in 10 mL of 1.0 M KOH in
EtOH. The reaction mixture was refluxed for 1 h and then
allowed to cool to room temperature. The EtOH was evapo-
rated in vacuo, and the resulting salt was washed with 5 mL
of hexane to extract the nonsaponifiable matter, which was
discarded. The salt was then dissolved in 15 mL of H2O and
acidified with 6.0 M HCl followed by extraction (3 × 10 mL)
with ethyl ether. The organic extracts were put together and
the solvent evaporated in vacuo, obtaining 0.025 g of 9 for a
63% yield:3 1H NMR (CDCl3, 300 MHz) δ 5.43-5.27 (2H, m,
H-5, H-6), 3.8 (1H, dd, J ) 6.8 and 5.1 Hz, H-2), 3.43 (3H, s,
-OCH3), 2.02 (4H, m), 1.75 (2H, m, H-3), 1.49 (2H, m, H-4),
1.26 (14H, br s, CH2), 0.87 (3H, t, J ) 6.5 Hz, -CH3); 13C NMR
(CDCl3, 75 MHz) δ 179.9 (s, C-1), 130.8 (d), 128.7 (d), 80.1 (d,
C-2), 58.2 (q, -OCH3), 31.9 (t), 29.7 (t), 29.6 (t), 29.5 (t), 29.3
(t), 26.7 (t), 24.9 (t), 22.7 (t), 14.0 (q, CH3).
An tiba cter ia l Activity. Antibacterial activity against P.
aeruginosa (ATCC 27853), E. coli (ATCC 25922), S. aureus
(ATCC 25923), and S. faecalis-group D (ATCC 29212) was
determined following National Committee of Clinical Labora-
tory Standards (NCCLS).15 A 200-µL solution of the R-meth-
oxylated fatty acid in Mueller-Hinton broth was inoculated
with 105 colony-forming units in a 96-well plate. The minimal
inhibitory concentration (MIC) was determined after an
overnight incubation of the R-methoxylated acid and the
microorganisms at 37 °C. The MIC was determined by
observing the highest dilution of the fatty acid that inhibited
growth when compared to an uninoculated chemical-control
well. The generated data were taken from at least three
separate experiments in duplicate.
2-Hydr oxy-6(Z)-h exadecen oic acid. Into a 100-mL round-
bottom flask equipped with a magnetic stirrer was placed
trimethylsilyloxyhexadecenonitrile (0.58 g, 1.8 mmol) in 10 mL
of THF, 5 mL of concentrated HCl was added, and the reaction
mixture was heated at 65 °C for 24 h. The reaction mixture
was then cooled (ice bath) and made alkaline by the slow
addition of 10 mL of 50% NaOH. The reaction mixture was
steam-distilled until no more NH3 passed into the distillate,
H2O was then added (25 mL) followed by extraction with ether
(3 × 15 mL). After drying over Na2SO4, the ether was suction
filtered and evaporated in vacuo, affording 0.3 g (70% yield)
of the acid, which was used for the next step without further
purification: 1H NMR (CDCl3, 300 MHz) δ 5.38-5.28 (2H, m,
H-5, H-6), 4.22 (1H, dd, J ) 7.2, 4.2 Hz, H-2), 2.20 (2H, m),
1.66 (2H, m), 1.45 (2H, m), 1.25 (16H, br s, CH2), 0.85 (3H, t,
J ) 6.5 Hz, -CH3); 13C NMR (CDCl3, 75 MHz) δ 178.7 (s, C-1),
130.7 (d), 128.7 (d), 70.2 (d, C-2), 33.6 (t), 31.9 (t), 29.5 (t), 29.3
(t), 29.2 (t), 27.2 (t), 26.7 (t), 24.9 (t), 22.6 (t), 14.0 (q, CH3).
Meth yl 2-m eth oxy-6(Z)-h exa d ecen oa te. Into a two-
necked round-bottom flask, equipped with a magnetic stirrer
and under nitrogen, was placed (Z)-2-hydroxy-6-hexadecenoic
acid (0.30 g, 1.1 mmol) dissolved in 5 mL of anhydrous DMSO.
Two equivalents of NaH, in 1.0 mL anhydrous DMSO, was
added, and the reaction mixture was stirred for 10 min.
Subsequently, an excess of MeI (4 equivalents) was slowly
added, and the reaction mixture was stirred for an additional
20 min. The reaction mixture was finally extracted with
hexane (3 × 10 mL), dried over MgSO4, and concentrated in
vacuo affording 0.17 g (51% yield) of the already reported
methoxylated methyl ester:3,14 IR (neat) νmax 3000, 2920, 2850,
1740, 1650, 1465, 1355, 1260, 1195, 1140, 720 cm-1; 1H NMR
(CDCl3, 300 MHz) δ 5.39-5.25 (2H, m, H-5, H-6), 3.74 (1H, t,
J ) 6.5 Hz, H-2), 3.73 (3H, s, -CO2CH3), 3.36 (3H, s, -OCH3),
2.28 (4H, m, H-5, H-8), 1.99 (2H, m, H-3), 1.69 (2H, m, H-4),
Ack n ow led gm en t . This work was supported by the
National Institutes of Health (NIH) under grant no.
5SO6GM08102. A.E. thanks the University of Puerto Rico
FIPI program for a doctoral fellowship. HREIMS determina-
tions were performed by Mr. Rau´l Blanco at the University of
Puerto Rico through the Materials Characterization Center
(MCC). Support from the NIH-RCMI program (grant 5G1-
2RR03641) is also acknowledged.
Refer en ces a n d Notes
(1) Ayanoglu, E.; Popov, S.; Kornprobst, J . M.; Aboud-Bichara, A.;
Djerassi, C. Lipids 1983, 18, 830-836.
(2) Ayanoglu, E.; Kornprobst, J . M.; Aboud-Bichara, A.; Djerassi, C.
Tetrahedron Lett. 1983, 24, 1111-1114.
(3) Carballeira, N.; Sepu´lveda, J . Lipids 1992, 27, 72-74.
(4) Carballeira, N.; Colo´n, R.; Emiliano, A. J . Nat. Prod. 1998, 61, 675-
676.
(5) Gerwick, W. H.; Reyes, S.; Alvarado, B. Phytochemistry 1987, 26,
1701-1704.
(6) Kobayashi, S.; Tsuchiya, Y.; Mukaiyama, T. Chem. Lett. 1991, 537-
540.
(7) Odinokov, V. N.; Galeeva, R. I.; Botsman, L. P.; Gladysheva, E. V.
Khim. Prir. Soedin. 1995, 6, 901-904.
(8) Yoshida, J .; Matsunaga, S.; Ishichi, Y.; Maekawa, T.; Isoe, S. J . Org.
Chem. 1991, 56, 1307-1309.
(9) Zelles, L.; Bai, Q. Y. Soil Biol. Biochem. 1993, 25, 495-507.
(10) Sebedio, J . L.; Ackman, R. G. J . Am. Oil Chem. Soc. 1979, 56, 15-
21.
(11) Ackman, R. G.; Sebedio, J . L. J . Chromatogr. Sci. 1978, 16, 204-
1.25 (14 H, br s, -CH2-), 0.87 (3H, t, J ) 6.5 Hz, -CH3); 13
C
206.
(12) Myrsina, R. A.; Sybchev, M. A.; Pogrebryak, R. S.; Svishchuk, A. A.
Fiziol. Akt. Veshchestva 1977, 9, 68-70.
NMR (CDCl3, 75 MHz), δ 173.2 (s, C-1), 130.6 (d), 128.8 (d),
80.5 (d, C-2), 58.0 (q, -OCH3), 51.8 (q, -CO2CH3), 32.4 (t, C-3),
31.9 (t, C-14), 29.6 (t), 29.57 (t), 29.54 (t), 29.3 (t), 29.2 (t), 27.2
(t, C-8), 26.8 (t, C-5), 25.2 (t), 22.6 (t, C-15), 14.0 (q, CH3); GC-
MS (70 eV) m/z 298 [M+] (1), 266 (2), 239 (5), 207 (4), 206 (4),
180 (5), 150 (6), 136 (6), 127 (6), 124 (5), 123 (8), 121 (8), 117
(6), 111 (16), 110 (9), 109 (22), 108 (5), 104 (100), 98 (6), 97
(23), 96 (23), 95 (68), 94 (15), 93 (19), 89 (5), 87 (16), 85 (11),
(13) Hayashi, A.; Nishimura, Y. Kinki Daigaku Rikogakubu Kenkyu
Hokoku 1984, 20, 107-113.
(14) Soderquist, J . A.; Rosado, I.; Marrero, Y. Tetrahedron Lett. 1998, 39,
3115-3116.
(15) Finegold, S. M.; Baron, E. J . Bailey and Scott’s Diagnostic Micro-
biology; C. V. Mosby: St. Louis, 1986; pp 173-201.
NP980274O