Enantioselective organocatalysis-based synthesis of 3-hydroxy fatty acids and fatty γ-lactones

Article abstract of DOI:10.3390/molecules24112081

3-Hydroxy fatty acids have attracted the interest of researchers, since some of them may interact with free fatty acid receptors more effectively than their non-hydroxylated counterparts and their determination in plasma provides diagnostic information regarding mitochondrial deficiency. We present here the development of a convenient and general methodology for the asymmetric synthesis of 3-hydroxy fatty acids. The enantioselective organocatalytic synthesis of terminal epoxides, starting from long chain aldehydes, is the key-step of our methodology, followed by ring opening with vinylmagnesium bromide. Ozonolysis and subsequent oxidation leads to the target products. MacMillan’s third generation imidazolidinone organocatalyst has been employed for the epoxide formation, ensuring products in high enantiomeric purity. Furthermore, a route for the incorporation of deuterium on the carbon atom carrying the hydroxy group was developed allowing the synthesis of deuterated derivatives, which may be useful in biological studies and in mass spectrometry studies. In addition, the synthesis of fatty γ-lactones, corresponding to 4-hydroxy fatty acids, was also explored.

Full text of DOI:10.3390/molecules24112081

molecules
Article
Enantioselective Organocatalysis-Based Synthesis of
3-Hydroxy Fatty Acids and Fatty γ-Lactones
Asimina Bourboula, Dimitris Limnios, Maroula G. Kokotou, Olga G. Mountanea and
George Kokotos *
Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 15771,
Greece; minabour@chem.uoa.gr (A.B.); dlimnios@chem.uoa.gr (D.L.); mkokotou@chem.uoa.gr (M.G.K.);
olgamount@chem.uoa.gr (O.G.M.)
* Correspondence: gkokotos@chem.uoa.gr; Tel.: +30-210-727-4462; Fax: +30-210-727-4761
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 17 March 2019; Accepted: 27 May 2019; Published: 31 May 2019
Abstract: 3-Hydroxy fatty acids have attracted the interest of researchers, since some of them may
interact with free fatty acid receptors more effectively than their non-hydroxylated counterparts and
their determination in plasma provides diagnostic information regarding mitochondrial deficiency.
We present here the development of a convenient and general methodology for the asymmetric
synthesis of 3-hydroxy fatty acids. The enantioselective organocatalytic synthesis of terminal epoxides,
starting from long chain aldehydes, is the key-step of our methodology, followed by ring opening
with vinylmagnesium bromide. Ozonolysis and subsequent oxidation leads to the target products.
MacMillan’s third generation imidazolidinone organocatalyst has been employed for the epoxide
formation, ensuring products in high enantiomeric purity. Furthermore, a route for the incorporation
of deuterium on the carbon atom carrying the hydroxy group was developed allowing the synthesis of
deuterated derivatives, which may be useful in biological studies and in mass spectrometry studies.
In addition, the synthesis of fatty γ-lactones, corresponding to 4-hydroxy fatty acids, was also explored.
Keywords: deuterated fatty acids; epoxides; hydroxy fatty acids; γ-lactones; organocatalysis
1. Introduction
Saturated and unsaturated fatty acids (FAs), as well as hydroxy fatty acids (HFAs) are components
of biomolecules and have been shown to exert cellular effects through G protein–coupled receptors
named free fatty acid receptors (FFA1–FFA4) and hydroxycarboxylic acid receptors (HCA1–HCA3) [
A recent study has shown that the G protein-coupled receptor 84 (GPR84) is activated by 2-hydroxy or
3-hydroxy medium chain fatty acids more effectively than by their non-hydroxylated counterparts [ ].
3-Hydroxy fatty acids are produced in mitochondria by -oxidation [ ] and are constituents of
inflammatory lipopolysaccharides [ ]. The determination of 3-hydroxy fatty acids in plasma or
tissue cultures provides diagnostic information regarding medium/short-chain mitochondrial L-3
hydroxyacyl coenzyme A dehydrogenases (M/SCHAD) deficiency [ ]. Recently, a method for the
1].
2
β
3
4
5
quantitative profiling of 3-hydroxy fatty acids as environmental markers of endotoxin in occupational
and environmental samples has been developed, using liquid chromatography coupled to tandem
mass spectrometry [6].
Several methods for the synthesis of 3-hydroxy acids are known in the literature. For example,
these hydroxy acids may be synthesized by the reduction of
the reducing agent may lead either to racemic or to chiral products [
3-hydroxy carboxylic acids employs an aldol-type reaction of unmasked iodoacetic acid with carbonyl
compounds promoted by samarium iodide [ ]. Another approach based on the Reformatsky reaction
β-keto esters, while the choice of
7,8]. An efficient synthesis of
9
has been applied for the synthesis of medium chain
β-hydroxy esters [10]. Recently, the synthesis of
Molecules 2019, 24, 2081; doi:10.3390/molecules24112081
www.mdpi.com/journal/molecules

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3-hydroxylauric acid by
γ
-alkylation of doubly deprotonated ethyl acetoacetate followed by reduction
of the β-keto moiety and ester hydrolysis has been reported [11]. 3-Hydroxy fatty acids may be also
synthesized via the opening of chiral long chain terminal epoxides by Me3SiCN in the presence
of TBAF, followed by hydrolysis of the resulting nitriles [12]. Another approach employs the ring
opening of chiral 2-(2-benzyloxyethyl)-oxirane by a long chain alkylmagnesium bromide, followed by
functional group transformations to give 3-hydroxy fatty acids [13]. The aim of the present study was
the development of a convenient general methodology for the asymmetric synthesis of 3-hydroxy fatty
acids. An organocatalytic step using an imidazolidinone catalyst was employed for the induction of
chirality. In addition, a synthetic route to deuterated 3-hydroxy fatty acids is presented. The synthesis
of 4-hydroxy fatty acids was also studied and applied to the synthesis of a fatty acid ester of a 4-hydroxy
fatty acid.
2. Results and Discussion
Organocatalysis has been recognized as a powerful methodology in asymmetric catalysis,
complementing metal catalysis and biocatalysis and offering new opportunities for the enantioselective
synthesis of biomolecules [14]. The organocatalytic formation of epoxides was selected as the
key-step of our asymmetric method, employing MacMillan’s imidazolidinone catalyst, which has
found a wide range of applications [15]. A number of different enantioselective methodologies for
the
α
-chlorination of aldehydes have been reported in literature, and the enantiomeric excess of
20].
the product depends on the catalyst, the chlorination agent and the reaction conditions [16
–
For the chlorination of long chain aldehydes, we selected a modified procedure employing
(2R,5S)-2-(tert-butyl)-3,5-dimethylimidazolidin-4-one trifluoroacetate as the organo-catalyst and
2,3,4,5,6,6-hexachlorocyclohexa-2,4-dien-1-one as the chlorination agent [21].
.
Figure 1. Previous work for the synthesis of 9-hydroxy fatty acids [22] (left) and current design plan
for the synthesis of 3-hydroxy fatty acids or 4-hydroxy fatty acid derivatives (right).

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We have recently presented the synthesis of 9-hydroxy fatty acids starting from monoprotected
diols and employing organocatalytic -chlorination, epoxide formation and ring opening by an
α
alkylmagnesium bromide (Figure 1, left). Through a multistep procedure (acetylation, debenzylation,
oxidation, deacetylation), 9-hydroxy fatty acids were obtained [22]. In the current work, we started from
commercially available long chain aldehydes and through an organocatalytic α-chlorination, chiral
terminal epoxides were synthesized, which were then opened either by vinylmagnesium bromide or by
allylmagnesium bromide (Figure 1, right). A different strategy, employing ozonolysis and subsequent
oxidation of the hydroxy alkenes, was followed to obtain the final 3-hydroxy fatty acids or 4-hydroxy
fatty acid derivatives
As depicted in Scheme 1, applying the selected protocol, commercially available long chain
aldehydes 1a
KOH, led in a one-pot procedure to the formation of terminal chiral epoxides 2a
high enantiomeric purity. Treatment of these epoxides with vinylmagnesium bromide resulted in the
ring opening and afforded 4-hydroxy terminal alkenes 3a in high yields The target compounds
–
d
were chlorinated and subsequent reduction by NaBH4, followed by treatment with
–d
in good yields and
–
d
.
4a–d, were obtained through ozonolysis of the alkene, followed by a Pinnick oxidation (Scheme 1).
Scheme 1. Reagents and conditions: (a) 2,3,4,5,6,6-hexachlorocyclohexa-2,4-dien-1-one, (2R,5S)-2-(tert-butyl)-
3,5-dimethylimidazolidin-4-one trifluoroacetate (20%), THF, r.t., 15 min, (b) NaBH4, EtOH, 0 ◦C, 30 min,
(c) KOH/EtOH/H2O, r.t., 15 min, (d) vinylmagnesium bromide 1M, CuI, dry THF,
−
78 ◦C, overnight,
(e) O3, CH2Cl2/pyridine 9:1,
−
78 ◦C, (f) i. Ar, 5 min, ii. Me2S, 0 ◦C, 1 h, (g) i. MeCN, t-BuOH, H2O,
2-methylbut-2-ene, NaH2PO4, NaClO2/H2O, r.t., 2 h, ii. Na2SO3.
3-Hydroxy fatty acids are of high biological importance and thus, their deuterated analogs could
be useful in biology and in mass spectrometry as internal standards. When a hydrogen atom of a
bioactive compound is replaced by deuterium, the deuterated derivative may present altered metabolic
stability [23].
Recently the FDA has approved the first deuterated drug [24], signifying a new era for research on
deuterated bioactive compounds. Thus, we developed a method for the incorporation of a deuterium
at the 3-position on the carbon atom carrying the hydroxy group. Our approach for the synthesis of
deuterated 3-hydroxy palmitic acid is shown in Scheme 2. Deuterated epoxide
6 was obtained in low
yield. Apparently the replacement of the deuterium by chlorine occurs in lower yield in comparison to
the replacement of hydrogen.
First, pentadecanal 1c was converted into the corresponding
treatment with D2O in the presence of triethylamine [25]. Organocatalytic
by reduction with NaBH4 and subsequent treatment with KOH, afforded in a one-pot procedure the
deuterated epoxide . For the -chlorination, d,l-proline used as the catalyst and N-chlorosuccinimide
α
,
α
-dideuterated derivative
5 by
α
-chlorination of , followed
5
6
α
as the chlorinating agent, since deuterated derivatives used as internal standards in mass spectrometry
studies are not needed to be chiral compounds. Then, using similar reactions with those previously
described, the deuterated hydroxy alkene
The degree of deuteration in compound was determined using liquid chromatography-high resolution
mass spectrometry (LC/HRMS) as depicted in Figure 2. The extracted ion chromatograms for m/z
272.2341 (corresponding to deuterated derivative ) and m/z 271.2279 (corresponding to non-deuterated
7 was obtained and converted into product 8 (Scheme 2).
8
8

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analog of 8) are shown in Figure 2A,B, while Figure 2C,D present the corresponding mass spectra.
The deuteration degree of compound 8 was estimated to be 95.8%.
Scheme 2. Reagents and conditions: (a) D2O, Et3N, 100 ◦C, 1 h, (b) N-chlorosuccinimide, d,l-proline,
CH2Cl2, r.t., overnight, (c) NaBH4, EtOH, 0 ◦C, 15 min, (d) KOH/EtOH/H2O, r.t., 30 min, (e)
vinylmagnesium bromide 1M, CuI, dry THF,
−
78 ◦C, overnight, (f) O3, CH2Cl2/pyridine 9:1, 78 ◦C, (g)
−
i. Ar, 5 min, ii. Me2S, 0 ◦C, 1 h, (h) i. MeCN, t-BuOH, H2O, 2-methylbut-2-ene, NaH2PO4, NaClO2/H2O,
r.t., 2 h, ii. Na2SO3.
Figure 2. Extracted ion chromatograms for m/z 272.2341 (A) and m/z 271.2279 (B) and their corresponding
mass spectra (C) and (D).
To extend our studies and in an effort to synthesize 4-hydroxy fatty acids derivatives, a similar
procedure was explored. As presented in Scheme 3, the ring opening of epoxides 2b and 10 was carried
out by treatment with allylmagnesium bromide to afford 5-hydroxy terminal alkenes 11a
yields. Ozonolysis of these compounds, followed by treatment with PPh3 led to a mixture of lactols
12a and lactones 13a . Jones oxidation of such mixtures resulted in full conversion to lactones 13a
Both lactones are naturally occurring products found either in insects or in food stuff [26–28].
,b in high
,
b
,
b
,b.
To avoid lactonization, the hydroxyl functionality of 5-hydroxy terminal alkenes has to be
derivatized. Such a synthesis leading to biologically relevant 4-(palmitoyloxy)octadecanoic acid
(4-PAHSA) is shown in Scheme 4. Fatty acid esters of hydroxy fatty acids (FAHFAs) have been recently
identified as a novel class of endogenous lipids that present antidiabetic and/or anti-inflammatory
properties [29
group (5-, 9-, etc.) have been reported and synthetic routes to FAHFAs and HFAs, where the hydroxyl
is at a position higher to 5-, have been developed [22 32 33]. FAHFAs containing the ester group at the
4-position have not yet reported and thus, we decided to synthesize such a derivative. Epoxide 15
–31]. Various families of FAHFAs varying in the chain length and the position of the ester
,
,

Molecules 2019, 24, 2081
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was synthesized using d,l-proline as the catalyst and N-chlorosuccinimide for the
α
-chlorination step,
followed by reduction with NaBH4 and treatment with KOH. Treatment of 15 with allylmagnesium
bromide afforded hydroxy alkene 16 in high yield, which was coupled with palmitic acid, using
N-ethyl-N0-(3-dimethylaminopropyl)carbodiimide (EDC) as the coupling agent in the presence of
4-(dimethylamino)pyridine (DMAP). Ozonolysis of 17, followed by a Pinnick oxidation, as previously
described, gave 4-PAHSA 18.
Scheme 3. Reagents and conditions: (a) 2,3,4,5,6,6-hexachlorocyclohexa-2,4-dien-1-one, (2R,5S)-2-(tert-butyl)-
3,5-dimethylimidazolidin-4-one trifluoroacetate (20%), THF, r.t., 15 min, (b) NaBH4, EtOH, 0 ◦C, 30 min,
(c) KOH/EtOH/H2O, r.t., 15 min, (d) allylmagnesium bromide 1M, CuI, dry THF,
−
40 ◦C, 1 h, (e) O3,
CH2Cl2,
−
78 ◦C, (f) i. O2, 5 min., ii. Ar, 5 min, (g) PPh3, dry CH2Cl2, r.t., overnight, (h) Jones oxidation.
Scheme 4. Reagents and conditions: (a) N-chlorosuccinimide, d,l-proline, CH2Cl2, r.t., overnight, (b)
NaBH4, EtOH, 0 ◦C, 15 min, (c) KOH/EtOH/H2O, r.t., 30 min, (d) allylmagnesium bromide 1M, CuI,
dry THF,
CH2Cl2/pyridine 9:1,
NaH2PO4, NaClO2/H2O, r.t., 2 h, ii. Na2SO3.
−
40 ◦C, 1 h, (e) CH3(CH2)14COOH, EDC, Et3N, 4-DMAP, dry CH2Cl2, r.t., overnight, (f) O3,
−
78 ◦C, (g) i. Ar, ii. Me2S, 0 ◦C, 1 h, (h) i. MeCN, t-BuOH, H2O, 2-methylbut-2-ene,
3. Experimental Section
3.1. General Information
All reactions were monitored by analytical thin-layer chromatography (TLC) using plates precoated
with silica gel (0.2 mm, 60 Å pore size) impregnated with a fluorescent indicator (254 nm). TLC plates
were visualized by exposure to ultraviolet light (UV) and then stained with 12-molybdophosphoric
acid hydrate in EtOH followed by brief heating on a hot plate.
1H-NMR spectra were recorded in CDCl3 at 200 MHz (Mercury, Varian, Darmstadt, Germany).
Data were reported as follows: chemical shifts in ppm from TMS with the solvent resonance as the
internal standard (CDCl3,
δ 7.26 ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m
= multiplet, br = broad signal), coupling constants (Hz) and integration. Proton-decoupled carbon

Molecules 2019, 24, 2081
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nuclear magnetic resonance spectra (13C-NMR) were recorded at 50 MHz. Chemical shifts were
expressed in parts per million (ppm, scale) downfield from TMS and are referenced to the carbon
resonances of the solvent (CDCl3, 77.0). High-resolution mass spectra (HRMS) were recorded on a
Maxis Impact QTOF (Bruker, Bremen, Germany) and a 4600 Triple TOF (AB Sciex, Singapore). Optical
rotations ([
20) were measured on an AA-65 series (Optical Activity Ltd., Bury, UK) polarimeter and
melting points (m.p.) were measured on a Buchi 530 apparatus (Buchi, Flawil, Switzerland).
Enantiomeric excesses of 4a were determined by chiral LC/HRMS analysis using a Chiralpak
AD-RH column and acetonitrile/H2O (95:5) containing 0.1% formic acid as the mobile phase (flow rate
δ
δ
α
]
D
–d
0.3 mL/min). Extracted ion chromatograms for the determination of enantiomeric excesses of 4a–d are
presented in the Supplementary Materials.
3.2. Synthesis and Characterization
3.2.1. General Procedure for the Synthesis of Chiral Epoxides 2a–d, 10
To a solution of (2R,5S)-2-(tert-butyl)-3,5-dimethylimidazolidin-4-one trifluoroacetate (57 mg,
0.20 mmol) in THF (0.5 mL), 2,3,4,5,6,6-hexachlorocyclohexa-2,4-dien-1-one (331 mg, 1.10 mmol) was
added and the solution was stirred for 5 min, before the aldehyde (1.00 mmol) was added. The reaction
mixture was stirred for 30 min at room temperature and was cooled to 0 ◦C, before EtOH (0.6 mL) and
NaBH4 (121 mg, 3.20 mmol) were added. After 10 min, the medium was warmed to room temperature
for 5 min, before a freshly prepared solution of aqueous KOH (1.70 g KOH diluted in 2.7 mL water) and
EtOH (1.3 mL) were added and the resulting mixture was stirred vigorously for 30 min. Then, water
(
1 × 20 mL) was added to the mixture before it was extracted with Et2O (3
×
10 mL), washed with
brine (1
×
20 mL), dried over Na2SO4, filtered and concentrated under reduced pressure. Purification
of the resulting residue by silica gel chromatography (petroleum ether 40–60 ◦C/diethyl ether, 9:1 or
8:2) afforded the title compounds.
(R)-2-Nonyloxirane (2a). Colorless oil, 129 mg, yield: 76%; Rf value: (pet. ether:diethyl ether = 9:1) 0.42;
20
20
[
δ
α
]
−
5.80 (c 1.0, CHCl3), [ref. [18], for S-enantiomer: [
2.85–2.76 (m, 1H, OCH), 2.64 (dd, J = 5.0, 4.1 Hz, 1H, OCHH), 2.36 (dd, J = 5.1, 2.7 Hz, 1H, OCHH),
CH2), 0.81 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
52.0, 46.7, 32.4, 31.7, 29.4,
α
]
+6.34 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
D
D
1.64–0.98 (m, 16H, 8
29.3, 29.2, 25.8, 22.5, 13.9.
×
δ
(R)-2-Dodecyloxirane (2b). Colorless oil, 174 mg, yield 82%; Rf value: (pet. ether:diethyl ether = 9:1)
20
20
0.37; [
(m, 1H, OCH), 2.72 (dd, J = 5.0, 4.0 Hz, 1H, OCHH), 2.44 (dd, J = 5.1, 2.7 Hz, 1H, OCHH), 1.57–1.16 (m,
22H, 11 52.5, 47.2, 32.7, 32.1, 29.8, 29.7, 29.6,
CH2), 0.86 (t, J = 6.2 Hz, 3H, CH3); 13C-NMR (CDCl3)
26.2, 22.9, 14.3.
α
]
+4.70 (c 1.0, CHCl3), [ref. [34], [
α
]
+4.30 (c 1.42, CHCl3)]; 1H-NMR (CDCl3)
δ 2.92–2.84
D
D
×
δ
(R)-2-Tridecyloxirane (2c). Colorless oil, 179 mg, yield 79%; Rf value: (pet. ether:diethyl ether = 9:1) 0.31;
20
20
[
α
]
+5.70 (c 0.5 CHCl3), [ref. [35], [
OCH), 2.57 (dd, J = 5.9, 4.0 Hz, 1H, OCHH), 2.29 (dd, J = 5.1, 2.7 Hz, 1H, OCHH), 1.48–1.05 (m, 24H, 12
CH2), 0.77 (t, J = 5.4 Hz, 3H, CH3); 13C-NMR (CDCl3)
51.8, 46.5, 32.4, 31.7, 29.5, 29.4, 29.3, 29.2, 25.8,
22.5, 13.8.
α
]
+6.54 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
δ 2.79–2.70 (m, 1H,
D
D
×
δ
(R)-2-Pentadecyloxirane (2d). Colorless oil, 211 mg, yield 83%; Rf value: (pet. ether:diethyl ether = 8:2)
0.37; [ 2.89–2.80
20 +5.00 (c 1.0, CHCl3), [ref. [36], [ 20 +5.43 (c 1.4, CHCl3)]; 1H-NMR (CDCl3)
(m, 1H, OCH), 2.67 (dd, J = 5.0, 4.0 Hz, 1H, OCHH), 2.39 (dd, J = 5.1, 2.7 Hz, 1H, OCHH), 1.53–1.11 (m,
28H, 14 52.1, 46.8, 32.4, 31.9, 29.6, 29.5, 29.4,
CH2), 0.83 (t, J = 5.4 Hz, 3H, CH3); 13C-NMR (CDCl3)
29.3, 25.9, 22.6, 14.0.
α
]
D
α
]
D
δ
×
δ
(R)-2-Octyloxirane (10). Colorless oil, 117 mg, yield 75%; Rf value: (pet. ether:diethyl ether = 9:1) 0.35;
20
20
[
δ
α
]
+8.00 (c 1.0, CHCl3) [ref. [37], for S-enantiomer: [
α
]
D
−
8.20 (c 1.03, CHCl3)]; 1H-NMR (CDCl3)
D
2.89–2.80 (m, 1H, OCH), 2.68 (dd, J = 5.0, 4.0 Hz, 1H, OCHH), 2.40 (dd, J = 5.1, 2.7 Hz, 1H, OCHH),

Molecules 2019, 24, 2081
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1.53–1.11 (m, 14H, 7
29.3, 29.1, 25.9, 22.5, 13.9.
×
CH2), 0.83 (t, J = 6.4 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ
52.2, 46.9, 32.4, 31.7, 29.4,
3.2.2. General Procedure for the Synthesis of Racemic Epoxides 6, 15
To a solution of
5 or 14 (1.00 mmol) in CH2Cl2 (5 mL), d,l-proline (115 mg, 0.10 mmol) and
N-chlorosuccinimide (174 mg, 1.30 mmol) were added and the reaction mixture was stirred for 16 h
at room temperature. The reaction mixture was cooled to 0 ◦C, before NaBH4 (121 mg, 3.20 mmol)
and EtOH (1 mL) were added. After 10 min, the medium was warmed to room temperature for 5 min
before a freshly prepared solution of aqueous KOH (2.25 g KOH diluted in 3.4 mL distilled water)
and EtOH (1.7 mL) were added and the resulting mixture was stirred vigorously for 30 min. At this
stage, water (10 mL) was added to the mixture before it was extracted with Et2O (1
×
10 mL), saturated
aqueous solution of NH4Cl (1 10 mL) and brine (1 10 mL). The combined organic layers were dried
×
×
over Na2SO4 and concentrated in vacuo. The resulting residue purified by column chromatography
(petroleum ether 40–60 ◦C/diethyl ether, 9:1 or 8:2).
2-Tridecyloxirane-2-d (
1H-NMR (CDCl3)
2.68 (d, J = 5.0 Hz, 1H, OCHH), 2.40 (d, J = 5.0 Hz, 1H, OCHH), 1.53–1.03 (m, 24H,
12
CH2), 0.84 (t, J = 6.2 Hz, 3H, CH3); 13C-NMR (CDCl3)
6). Colorless oil, 80 mg, yield 35%; Rf value: (pet. ether:diethyl ether = 8:2) 0.48;
δ
×
δ 51.8 (t, J = 25.0 Hz, OCD), 46.8, 32.3, 31.9,
29.6, 29.5, 29.4, 29.3, 25.9, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M + Na]+ (C15H29DONa+)
requires m/z 250.2252, found m/z 250.2249.
2-Tetradecyloxirane (15). Colorless oil, 195 mg, yield 81%; Rf value: (pet. ether:diethyl ether = 9:1) 0.41;
1H-NMR (CDCl3)
δ
2.87–2.79 (m, 1H, OCH), 2.66 (dd, J = 5.1, 4.0 Hz, 1H, OCHH), 2.38 (dd, J = 6.0, 2.0
Hz, 1H, OCHH), 1.58–0.98 (m, 26H, 13 52.1,
46.8, 32.4, 31.8, 29.6, 29.5, 29.4, 29.3, 25.9, 22.6, 13.9 [38].
×
CH2), 0.83 (t, J = 6.4 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ
3.2.3. General Procedure for the Synthesis of 4-Hydroxy Terminal Alkenes 3a–d, 7
To a flame-dried round flask, degassed and under argon atmosphere, copper(I) iodide (38 mg,
0.20 mmol) and vinylmagnesium bromide (1M solution in THF, 2.0 mL, 2.00 mmol) were added and
cooled to
dropwise and the reaction mixture was left stirring at
allowed to warm to room temperature and after treatment with a saturated aqueous solution of NH4Cl
−
78 ◦C. Then, a solution of the epoxide (1.00 mmol) in anhydrous THF (5 mL) was added
−
78 ◦C overnight. The reaction mixture was
(1
(1
×
5 mL) was extracted with Et2O (3
30 mL), dried over Na2SO4, filtered and concentrated under reduced pressure. Purification of
×
10 mL). The combined organic layers were washed with brine
×
the resulting residue by silica gel chromatography (petroleum ether 40–60 ◦C/diethyl ether, 9:1 or 8:2)
afforded the desired compounds.
(R)-Tridec-1-en-4-ol (3a). Colorless oil, 169 mg, yield 85%; Rf value: (pet. ether:diethyl ether = 8:2) 0.48;
20
20
[α
]
−
6.70 (c 1.0, CHCl3) [ref. [39], [
α
]
−
7.50 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
δ 5.87–5.68 (m, 1H,
D
D
=CH), 5.15–5.04 (m, 2H, =CH2), 3.66–3.54 (m, 1H, CHOH), 2.32–2.02 (m, 3H, CH2CH, OH), 1.49–1.09
(m, 16H, 8 × CH2), 0.84 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3) δ 134.9, 117.7, 70.6, 41.8, 36.7, 31.8,
29.6, 29.5, 29.3, 25.6, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M + Na]+ (C13H26ONa+) requires
m/z 221.1876, found m/z 221.1875.
Hexadec-1-en-4-ol (3b). Colorless oil, 195 mg, yield 81%; Rf value (pet. ether/diethyl ether 9:1) 0.52;
20
20
[α
]
−
5.00 (c 1.0, CHCl3) [ref. [40], [
α
]
−
5.50 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
δ 5.92–5.71 (m, 1H,
D
D
=CH), 5.17–5.06 (m, 2H, =CH2), 3.67–3.51 (m, 1H, CHOH), 2.34–2.01 (m, 2H, CH2CH), 1.83 (s, 1H, OH),
1.48–0.96 (m, 22H, 11
×
CH2), 0.86 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ 134.9, 117.8, 70.6, 41.9,
36.8, 31.9, 29.6, 29.3, 25.6, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M + Na]+ (C16H32ONa+)
requires m/z 263.2345, found m/z 263.2340 [41].
(R)-Heptadec-1-en-4-ol (3c). Colorless oil, 211 mg, yield 83%; Rf value (pet. ether:diethyl ether = 9:1)
0.46; [α] α] δ 5.90–5.70
20 + 4.00 (c 1.0, CHCl3), [ref. [35], [ 20 +4.92 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
D D

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(m, 1H, =CH), 5.12–5.05 (m, 2H, =CH2), 3.68–3.53 (m, 1H, CHOH), 2.32–2.02 (m, 3H, CH2CH, OH),
1.49–1.10 (m, 24H, 12
×
CH2), 0.85 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ 134.9, 117.7, 70.6, 41.9,
36.7, 31.9, 29.6, 29.3, 25.6, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M + Na]+ (C17H34ONa+)
requires m/z 277.2502, found m/z 277.2503.
◦
◦
(R)-Nonadec-1-en-4-ol (3d). White solid, 220 mg, m.p.: 50–52 C (ref. [42], 44–45 C), yield 79%; Rf
20
20
value (pet. ether:diethyl ether = 8:2) 0.57; [α]D −17.0 (c 0.50, CHCl3), [ref. [43], [α]D −18.33 (c 0.36,
1
CHCl3)]; H-NMR (CDCl3)
δ 5.90–5.69 (m, 1H, =CH), 5.12–5.04 (m, 2H, =CH2), 3.64–3.53 (m, 1H,
CHOH), 2.32–2.03 (m, 3H, CH2CH, OH), 1.41–1.09 (m, 28H, 14
13C-NMR (CDCl3)
138.6, 114.6, 71.3, 37.4, 36.4, 31.9, 30.0, 29.7, 29.3, 25.6, 22.6, 14.0; HRMS (ESI) exact
mass calculated for [M + Na]+ (C19H38ONa+) requires m/z 305.2815, found m/z 305.2811.
×
CH2), 0.85 (t, J = 5.8 Hz, 3H, CH3);
δ
Heptadec-1-en-4-d-4-ol ( ). Colorless oil, 194 mg, yield 76%; Rf value (pet. ether:diethyl ether = 7:3) 0.52;
1H-NMR (CDCl3)
5.91–5.70 (m, 1H, =CH), 5.13–5.05 (m, 2H, =CH2), 2.31–1.99 (m, 3H, CH2CH, OH),
1.41–1.14 (m, 24H, 12
7
δ
×
CH2), 0.85 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ 134.9, 117.8, 70.1 (t,
J = 20 Hz), 41.7, 36.6, 31.9, 29.6, 29.3, 25.6, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M + Na]+
(C17H33DONa+) requires m/z 278.2565, found m/z 278.2566.
3.2.4. General Procedure for the Synthesis of 5-Hydroxy Terminal Alkenes 11a,b, 16
To a flame-dried round flask, degassed and under argon atmosphere, copper(I) iodide (38 mg,
0.20 mmol) and allylmagnesium bromide (1M solution in THF, 2.0 mL, 2.00 mmol) were added and
cooled to
dropwise and the reaction mixture was left stirring at
to warm to room temperature and after treatment with a saturated aqueous solution of NH4Cl (5 mL)
was extracted with Et2O (3 10 mL). The combined organic layers were washed with brine (30 mL),
−
40 ◦C. Then, a solution of the epoxide (1.00 mmol) in anhydrous THF (5 mL) was added
−
40 ◦C for 2 h. The reaction mixture was allowed
×
dried over Na2SO4, filtered and concentrated under reduced pressure. Purification of the resulting
residue by silica gel chromatography (petroleum ether 40–60 ◦C/diethyl ether, 9:1 or 8:2) afforded the
desired products.
(R)-Tridec-1-en-5-ol (11a). Colorless oil, 151 mg, yield 76%; Rf value (pet. ether:diethyl ether = 9:1) 0.59;
[α] α] δ 5.92–5.72 (m,
20 +2.30 (c 0.9, MeOH), [ref. [37], [ 20 +2.40 (c 0.86, MeOH)]; 1H-NMR (CDCl3)
D D
1H, =CH), 5.06–4.92 (m, 2H, =CH2), 3.63–3.55 (m, 1H, CHOH), 2.25–2.04 (m, 2H, CH2CH=), 1.94 (s, 1H,
OH), 1.55–1.15 (m, 16H, 8 × CH2), 0.86 (t, J = 6.4 Hz, 3H, CH3); 13C-NMR (CDCl3) δ 138.6, 114.6, 71.4,
37.4, 36.4, 30.0, 29.7, 29.6, 29.2, 25.6, 25.5, 22.6, 22.4, 14.1.
(R)-Heptadec-1-en-5-ol (11b). Colorless oil, 193 mg, yield 76%; Rf value (pet. ether:diethyl ether = 9:1)
0.61; [
α
]
20 + 0.80 (c 0.5, CHCl3); 1H-NMR (CDCl3)
δ
5.94–5.74 (m, 1H, =CH), 5.09–4.93 (m, 2H, =CH2),
CH2, OH), 0.87 (t,
δ 138.6, 114.6, 71.4, 37.5, 36.4, 31.9, 31.7, 30.1, 29.6, 29.3, 25.6,
D
3.67–3.55 (m, 1H, CHOH), 2.31–2.00 (m, 2H, CH2CH=), 1.58–1.15 (m, 25H, 12
J = 6.0 Hz, 3H, CH3); 13C-NMR (CDCl3)
×
22.7, 14.1 [44].
Nonadec-1-en-5-ol (16). Colorless oil, 223 mg, yield 79%; Rf value (pet. ether:diethyl ether = 9:1) 0.53;
1H-NMR (CDCl3)
5.92–5.72 (m, 1H, =CH), 5.07–4.91 (m, 2H, =CH2), 3.64–3.53 (m, 1H, CHOH),
CH2), 0.86 (t, J = 6.3 Hz, 3H,
138.6, 114.6, 71.3, 37.4, 36.4, 33.2, 33.1, 31.9, 30.0, 29.7, 29.5, 29.3, 25.6, 22.6,
δ
2.26–2.04 (m, 2H, CH2CH=), 1.88 (s, 1H, OH), 1.57–1.24 (m, 28H, 14
×
CH3); 13C-NMR (CDCl3)
14.0 [45].
δ
3.2.5. General Procedure for the Synthesis of 3-Hydroxy Fatty Acids 4a–d, 8
Ozone was passed through a solution of 3a or (1.00 mmol) in a mixture of CH2Cl2 (4.5 mL)
and pyridine (0.5 mL) at
78 ◦C. Once the reaction solution had a persistent blue color, was Ar passed
–d
7
−
through until the solution was discolored, then dimethylsulfide (0.4 mL, 14.0 mmol) was added at 0 ◦C
and the reaction mixture was left stirring for 1 to 2 h. After concentration under reduced pressure, the
residue was oxidized to the desired 3-hydroxy fatty acid as described below.

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To a round-bottomed flask containing the aldehyde (1.00 mmol), MeCN (10 mL), t-BuOH (2 mL),
distilled H2O (0.5 mL), 2-methylbut-2-ene (0.5 mL), NaH2PO4 (48 mg, 0.40 mmol), aqueous solution
of NaClO2 (154 mg NaClO2 diluted in 1 mL water) were added at 0 ◦C. The reaction mixture was
left stirring for 2 h and then was quenched by the addition of Na2SO3 (101 mg, 0.80 mmol). After
acidification to pH 1 by the addition of a solution of 1N HCl, the reaction mixture was extracted
with Et2O (3
×
10 mL). The combined organic layers were washed with brine (30 mL), dried over
Na2SO4 and concentrated in vacuo. The resulting residue was purified by column chromatography
(CH2Cl2/MeOH 9:1 containing 10% CH3COOH) and recrystallized with hexane.
(R)-3-Hydroxydodecanoic acid (4a). White solid, 76 mg, m.p.: 63–64 ◦C (ref. [46], 67–68 ◦C), yield 35%; Rf
20
20
value (dichloromethane:methanol = 9:1) 0.37; [
CHCl3)]; 1H-NMR (CDCl3) δ 7.47 (s, 1H, COOH), 4.00 (s, 1H, CHOH), 2.55–2.34 (m, 2H, CH2COOH),
1.43–1.24 (m, 16H, 8 177.3, 68.2, 41.2, 36.4, 31.8,
CH2), 0.85 (t, J = 5.7 Hz, 3H, CH3); 13C-NMR (CDCl3)
29.6, 29.5, 29.3, 25.4, 22.6, 14.0; HRMS (ESI) exact mass calculated for [M
H]− (C12H23O3−) requires
α
]
−
15.80 (c 1.0, CHCl3), [ref. [47], [
α
]
−
16.90 (c 1.0,
D
D
×
δ
−
m/z 215.1653, found m/z 215.1634; LC-HRMS analysis: 95% ee, Chiralpak AD-RH, acetonitrile/H2O
(95:5) formic acid 0.1%, 0.3 mL/min, tR = 9.3 (minor), tR = 9.9 (major).
(R)-3-Hydroxypentadecanoic acid (4b). White solid, 119 mg, m.p.: 82–83 ◦C (ref. [48], 86–87 ◦C), yield 46%;
20
20
Rf value (dichloromethane:methanol = 9:1) 0.29; [
α
]
D
−
14.00 (c 1.0, CHCl3), [ref. [49], [
α
]
D
−
15.00
(c 1.0, CHCl3)]; 1H-NMR (CDCl3)
δ 4.06–3.97 (m, 1H, CHOH), 2.63–2.46 (m, 2H, CH2COOH), 1.57–1.01
(m, 22H, 11 × CH2), 0.85 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3) δ 177.4, 68.0, 41.0, 36.5, 31.9, 29.6,
29.6, 29.5, 29.4, 25.4, 22.7, 14.1; HRMS (ESI) exact mass calculated for [M
−
H]− (C15H29O3−) requires
m/z 257.2122, found m/z 257.2110; LC-HRMS analysis: 91% ee, Chiralpak AD-RH, acetonitrile/H2O
(95:5) formic acid 0.1%, 0.3 mL/min, tR = 12.7 (minor), tR = 14.7 (major).
(R)-3-Hydroxyhexadecanoic acid (4c). White solid, 106 mg, m.p.: 80–81 ◦C (ref. [50], 83–84 ◦C), yield
20
20
39%; Rf value (dichloromethane:methanol = 9:1) 0.32; [
12.60 (c 2.08, CHCl3)]; 1H-NMR (CDCl3)
4.02 (s, 1H, CHOH), 2.61–2.31 (m, 3H, CH2COOH, OH),
1.66–1.11 (m, 24H, 12 177.9, 68.0, 41.0,
CH2), 0.87 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
H]−
α
]
−
13.00 (c 2.0, CHCl3), [ref. [13], [α]
D
D
−
δ
×
δ
36.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.2, 25.4, 22.7, 14.1; HRMS (ESI) exact mass calculated for [M
(C16H31O3−) requires m/z 271.2279, found m/z 271.2274; LC-HRMS analysis: 89% ee, Chiralpak AD-RH,
acetonitrile/H2O (95:5) formic acid 0.1%, 0.3 mL/min, tR = 14.7 (minor), tR = 17.8 (major).
−
(R)-3-Hydroxyoctadecanoic acid (4d). White solid, 129 mg, m.p.: 82–84 ◦C (ref. [51], 88–90 ◦C), yield
20
20
43%; Rf value (dichloromethane:methanol = 9:1) 0.27; [
15.80 (c 1.0, CHCl3)]; 1H-NMR (CDCl3)
4.06–4.01 (m, 1H, CHOH), 2.62–2.39 (m, 3H, CH2COOH,
OH), 1.65–1.17 (m, 28H, 14 177.3, 68.0,
CH2), 0.87 (t, J = 6.4 Hz, 3H, CH3); 13C-NMR (CDCl3)
H]−
α
]
−
16.00 (c 1.0, CHCl3), [ref. [8], [α]
D
D
−
δ
×
δ
41.0, 36.5, 31.9, 29.7, 29.6, 29.5, 29.4, 25.4, 22.7, 14.1; HRMS (ESI) exact mass calculated for [M
(C18H35O3−) requires m/z 299.2592, found m/z 299.2572; LC-HRMS analysis: 92% ee, Chiralpak AD-RH,
acetonitrile/H2O (95:5) formic acid 0.1%, 0.3 mL/min, tR = 21.0 (minor), tR = 26.5 (major).
−
◦
3-Hydroxyhexadecanoic-3-d acid (
8
). White solid, 104 mg, m.p.: 80–82 C, yield 38%; Rf value (pet.
1
ether:diethyl ether = 7:3) 0.27; H-NMR (CDCl3)
J = 16.0 Hz, 1H, CHHCOOH), 2.03 (s, 1H, OH), 1.48–1.10 (m, 24H, 12
CH3); 13C-NMR (CDCl3)
δ
2.58 (d, J = 16.0 Hz, 1H, CHHCOOH), 2.45 (d,
CH2), 0.88 (t, J = 6.0 Hz, 3H,
177.3, 40.8, 36.4, 31.9, 29.7, 29.6, 29.5, 29.4, 25.4, 22.7, 14.1; HRMS (ESI) exact
×
δ
mass calculated for [M − H]− (C16H30DO3−) requires m/z 272.2341, found m/z 272.2331.
3.2.6. General Procedure for the Synthesis of Lactones 13a,b
Ozone passed through a solution of 11a
,
b
(1.00 mmol) in CH2Cl2 (10 mL) at
78 ◦C. Once the
−
reaction solution had a persisted blue color, O2 passed through for 5 min and then Ar, until the solution
was discolored. The reaction mixture was allowed to warm to room temperature and then, PPh3
(262 mg, 1.00 mmol) was added and left stirring overnight. The solution was concentrated in vacuo
and the resulting residue was purified by column chromatography (petroleum ether 40–60 ◦C/diethyl

Molecules 2019, 24, 2081
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ether, 8:2 or 7:3). Thus, a mixture of lactol/lactone was obtained, which was fully oxidized to the
desired lactone as described below.
To a solution of lactol/lactone (1.00 mmol) in acetone (10 mL) Jones solution 2 M (1.5 mL, 3.00 mmol)
was added dropwise at 0 ◦C and the reaction mixture was left stirring for 1 h. Then, the reaction mixture
was quenched by the addition of a saturated aqueous solution of NaHSO3 (10 mL) and extracted with
Et2O (3
×
10 mL). The combined organic layers were washed with brine (30 mL), dried over Na2SO4
and concentrated in vacuo. The resulting residue was purified by column chromatography (petroleum
ether 40–60 ◦C/diethyl ether, 7:3 or 6:4).
(R)-5-Octyldihydrofuran-2(3H)-one (13a). Colorless oil, 182 mg, yield 92%; Rf value (pet. ether:diethyl
20
ether = 7:3) 0.62; [
1H-NMR (CDCl3)
1.89–1.23 (m, 15H, 7
35.5, 31.7, 29.3, 29.2, 29.1, 28.8, 27.9, 25.1, 22.6, 14.0.
α
]
δ
20 + 42.80 (c 1.0, MeOH) [ref. [37], for S-enantiomer: [
α
]
−
43.10 (c 1.01, MeOH)];
D
D
4.52–4.39 (m, 1H, CH), 2.54–2.46 (m, 2H, CH2CO), 2.37–2.21 (m, 1H, CHHCH),
×
CH2, CHHCH), 0.84 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3)
δ
177.4, 81.0,
(R)-5-Dodecyldihydrofuran-2(3H)-one (13b). White solid, 226 mg, m.p.: 35–36 ◦C (ref. [52], 38–39 ◦C),
yield 89%; Rf value (pet. ether:diethyl ether = 7:3) 0.56; [
20 +7.60 (c 1.0, CHCl3); 1H-NMR (CDCl3)
α
]
D
δ
4.56–4.39 (m, 1H, CH), 2.56–2.44 (m, 2H, CH2CO), 2.38–2.22 (m, 1H, CHHCH), 1.93–1.56 (m, 3H, CH2,
CHHCH), 1.59–1.24 (m, 20H, 10 × CH2), 0.86 (t, J = 6.3 Hz, 3H, CH3); 13C-NMR (CDCl3) δ 177.3, 81.0,
35.5, 31.9, 29.6, 29.5, 29.4, 29.3, 28.8, 28.0, 25.2, 22.6, 14.1.
3.2.7. Nonadec-1-en-5-yl Palmitate (17)
To a solution of palmitic acid (1.0 g, 4.00 mmol) in dry CH2Cl2 (15 mL), EDC (770 mg, 4.00 mmol),
Et3N (0.6 mL, 4.00 mmol) and 4-DMAP (24 mg, 0.20 mmol) were added at 0 ◦C and the reaction mixture
was left stirring for 10 min. Then, a solution of alcohol 16 (300 mg, 1.00 mmol) in dry CH2Cl2 (10 mL)
was added and the mixture was left stirring at room temperature overnight. The reaction mixture was
washed sequentially with a saturated aqueous solution of NH4Cl (10 mL), an aqueous solution of 10%
NaHCO3 (10 mL), an aqueous solution of 10% citric acid (10 mL) and brine (15 mL). The combined
organic layers were dried over Na2SO4, concentrated in vacuo and the product was purified by column
chromatography (pet.ether 40–60 ◦C/ EtOAc 95:5). White solid; 458 mg, m.p.: 105–107 ◦C, yield 88%;
Rf value (pet. ether:EtOAc = 95:5) 0.44; 1H-NMR (CDCl3)
=CH2, CHCOO), 2.27 (t, J = 7.4 Hz, 2H, CH2COO), 2.10–2.00 (m, 2H, CH2CH=), 1.71–1.25 (m, 54H, 27
CH2), 0.87 (t, J = 6.4 Hz, 6H, 2 173.5, 137.9, 114.8, 73.4, 34.7, 34.1, 33.4,
CH3); 13C-NMR (CDCl3)
δ 5.88–5.70 (m, 1H, =CH), 5.05–4.83 (m, 3H,
×
×
δ
31.9, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 25.3, 25.1, 22.7, 14.1; HRMS (ESI) exact mass calculated for [M +
Na]+ (C35H68O2Na+) requires m/z 543.5112, found m/z 543.5101.
3.2.8. 4-(Palmitoyloxy)octadecanoic acid (18)
Ozone was passed through a solution of compound 17 (521 mg, 1.00 mmol) in a mixture of CH2Cl2
(4.5 mL) and pyridine (0.5 mL) at
78 ◦C. Once the reaction solution had a persistent blue color, Ar was
−
passed through until the solution was discolored, then dimethylsulfide (0.4 mL, 14.0 mmol) was added
at 0 ◦C and the reaction mixture was left stirring for 1 to 2 h. Then, after concentration under reduced
pressure, the residue was oxidized by a Pinnick oxidation. The desired product was obtained after
purification by column chromatography (pet. ether 40–60 ◦C/EtOAc 8:2). White solid, 210 mg, m.p.:
129–131 ◦C, yield 39%; Rf value (dichloromethane:methanol = 9:1) 0.34; 1H-NMR (CDCl3)
CH), 2.41–2.24 (m, 4H, 2 CH2COO), 1.95–1.78 (m, 4H, 2 CH2), 1.64–1.25 (m, 50H, 25
J = 5.9 Hz, 6H, 2
CH3); 13C-NMR (CDCl3)
δ
4.91 (s, 1H,
×
×
×
CH2), 0.87 (t,
×
δ
178.5, 173.7, 72.9, 34.5, 34.1, 31.9, 30.0, 29.7, 29.6, 29.−5,
29.4, 29.3, 29.2, 28.9, 25.2, 25.1, 22.7, 14.1; HRMS (ESI) exact mass calculated for [M
−
H]− (C34H65O4
)
requires m/z 537.4888, found m/z 537.4887.
3.2.9. 2,2-d2-Pentadecanal (5)
To a flame-dried round-bottom flask under argon atmosphere, pentadecanal (226 mg, 1.00 mmol),
D2O (1 mL) and triethylamine (0.01 mL, 0.10 mmol) were added and the mixture was left stirring in an

Molecules 2019, 24, 2081
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oil bath at 100 ◦C for 1 h. Then, the mixture was allowed to warm to room temperature and after the
addition of an aqueous solution of 1 N HCl, it was extracted with Et2O (2 10 mL). The organic layers
×
were washed successively with an aqueous solution of 10% NaHCO3 (10 mL) and brine (10 mL) and
then collected, dried over Na2SO4 and concentrated in vacuo. The aldehyde was immediately used for
the next step without further purification. Colorless oil, 185 mg, yield 81%; Rf value (pet. ether:diethyl
ether = 9:1) 0.37; 1H-NMR (CDCl3)
δ
9.59 (s, 1H, CHO), 1.46–1.06 (m, 24H, 12
×
CH2), 0.75 (t, J = 6.2 Hz,
3H, CH3); 13C-NMR (CDCl3)
δ 201.9, 43.6–42.1 (m, CD2) 31.7, 29.5, 29.4, 29.3, 29.2, 28.9, 22.5, 21.7, 13.8.
4. Conclusions
In conclusion, we have developed a convenient enantioselective synthesis of biologically important
3-hydroxy fatty acids. Our methodology employs as the key-step the organocatalytic synthesis of chiral
terminal epoxides using MacMillan’s third generation imidazolidinone organocatalyst thus ensuring
high enantiomeric purity. The subsequent ring opening by vinylmagnesium bromide, followed by
ozonolysis and oxidation leads to the target products. An approach for the synthesis of deuterated
3-hydroxy fatty acids is demonstrated, leading to deuterated derivatives, which can be useful in
biological studies and in mass spectrometry studies as internal standards. Furthermore, a similar
procedure using allylmagnesium bromide for the opening of epoxides leads to fatty
allows the synthesis of fatty acid asters of 4-hydroxy fatty acids.
γ-lactones and
Supplementary Materials: Supplementary Materials are available online.
Author Contributions: G.K. conceived and designed the experiments; A.M., D.L. and O.G.M. synthesized and
characterized the compounds; M.G.K. performed the mass spectrometry studies; A.M. and G.K. wrote the paper.
Funding: We would like to thank the Special Account for Research Grants of the National and Kapodistrian
University of Athens for the financial support (Grant 13300).
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Offermanns, S. Free fatty acid (FFA) and hydroxy carboxylic acid (HCA) receptors. Annu. Rev. Pharmacol. Toxicol.
2014, 54, 407–434. [CrossRef] [PubMed]
2.
Suzuki, M.; Takaishi, S.; Nagasaki, M.; Onozawa, Y.; Iino, I.; Maeda, H.; Komai, T.; Oda, T. Medium-chain
fatty acid-sensing receptor, GPR84, is a proinflammatory receptor. J. Biol. Chem. 2013, 288, 10684–10691.
[CrossRef] [PubMed]
3.
Jin, S.-J.; Hoppel, C.L.; Tserng, K.-Y. Incomplete fatty acid oxidation. The production and epimerization of
3-hydroxy fatty acids. J. Biol. Chem. 1992, 267, 119–125. [PubMed]
4.
5.
Raetz, C.R.; Whitfield, C. Lipopolysaccharide endotoxins. Annu. Rev. Biochem. 2002, 71, 635–700. [CrossRef]
Jones, P.M.; Bennett, M.J. Clinical applications of 3-hydroxy fatty acid analysis by gas chromatography–mass
spectrometry. Biochim. Biophys. Acta 2011, 1811, 657–662. [CrossRef]
6.
Uhlig, S.; Negård, M.; Heldal, K.K.; Straumfors, A.; Madsø, L.; Bakke, B.; Eduard, W. Profiling of 3-hydroxy
fatty acids as environmental markers of endotoxin using liquid chromatography coupled to tandem mass
spectrometry. J. Chromatogr. A 2016, 1434, 119–126. [CrossRef]
7.
8.
Oikawa, Y.; Sugano, K.; Yonemitsu, O. Meldrum’s acid in organic synthesis. 2. A general and versatile
synthesis of α-keto esters. J. Org. Chem. 1978, 43, 2087–2088. [CrossRef]
Ratovelomanana-Vidal, V.; Girard, C.; Touati, R.; Tranchier, J.P.; Ben Hassine, B.; Genêt, J.P. Enantioselective
hydrogenation of -keto esters using chiral diphosphine-ruthenium complexes: Optimization for academic
α
and industrial purposes and synthetic applications. Adv. Synth. Catal. 2003, 345, 261–274. [CrossRef]
Concellon, J.M.; Concellon, C. Aldol-type reactions of unmasked iodoacetic acid with carbonyl compounds
promoted by samarium diiodide: Efficient synthesis of carboxylic 3-hydroxyacids and their derivatives.
J. Org. Chem. 2006, 71, 4428–4432. [CrossRef]
9.
10. Sailer, M.; Dubicki, K.I.; Sorensen, J.L. The synthesis of medium-chain-length β-hydroxy esters via the
Reformatsky reaction. Synthesis 2015, 47, 79–82.

Molecules 2019, 24, 2081
12 of 13
11. Kaspersen, M.H.; Jenkins, L.; Dunlop, J.; Milligan, G.; Ulven, T. Succinct synthesis of saturated hydroxy fatty
acids and in vitro evaluation of all hydroxylauric acids at FFA1, FFA4 and GPR84. Med. Chem. Comm. 2017
8, 1360–1365. [CrossRef] [PubMed]
,
12. Guaragna, A.; De Nisco, M.; Pedatella, S.; Palumbo, G. Studies towards lipid A: A synthetic strategy for the
enantioselective preparation of 3-hydroxy fatty acids. Tetrahedron: Asymmetry 2006, 17, 2839–2841. [CrossRef]
13. Jakob, B.; Voss, G.; Gerlach, H. Synthesis of (S)- and (R)-3-hydroxyhexadecanoic acid. Tetrahedron: Asymmetry
1996, 7, 3255–3262. [CrossRef]
14. Comprehensive Enantioselective Organocatalysis: Catalysts, Reactions, and Applications; Dalko, P.I. (Ed.) Wiley-VCH:
Weinheim, Germany, 2013.
15. MacMillan, D.W.C. The advent and development of organocatalysis. Nature 2008, 455, 304–308. [CrossRef]
16. Brochu, M.P.; Brown, S.P.; MacMillan, D.W.C. Direct and enantioselective organocatalytic α-chlorination of
aldehydes. J. Am. Chem. Soc. 2004, 126, 4108–4109. [CrossRef]
17. Halland, N.; Braunton, A.; Bachmann, S.; Marigo, M.; Jørgensen, K.A. Direct organocatalytic asymmetric
α-chlorination of aldehydes. J. Am. Chem. Soc. 2004, 126, 4790–4791. [CrossRef]
18. Amatore, M.; Beeson, T.D.; Brown, S.P.; MacMillan, D.W.C. Enantioselective linchpin catalysis by SOMO
catalysis: An approach to the asymmetric alpha-chlorination of aldehydes and terminal epoxide formation.
Angew. Chem. Int. Ed. 2009, 48, 5121–5124. [CrossRef] [PubMed]
19. Kang, B.; Britton, R. A general method for the synthesis of nonracemic trans-epoxides: Concise syntheses of
trans-epoxide-containing insect sex pheromones. Org. Lett. 2007, 24, 5083–5086. [CrossRef]
20. Wang, L.; Cai, C.; Curran, D.P.; Zhang, W. Enantioselective α-chlorination of aldehydes with recyclable
fluorous (S)-pyrrolidine–thiourea bifunctional organocatalyst. Synlett 2010, 433–436. [CrossRef]
21. Kaplaneris, N.; Spyropoulos, C.; Kokotou, M.G.; Kokotos, C.G. Enantioselective organocatalytic synthesis of
2-oxopiperazines from aldehydes: Identification of the elusive epoxy lactone intermediate. Org. Lett. 2016
18, 5800–5803. [CrossRef]
,
22. Mountanea, O.G.; Limnios, D.; Kokotou, M.G.; Bourboula, A.; Kokotos, G. Asymmetric synthesis of saturated
hydroxy fatty acids and fatty acid esters of hydroxy fatty acids. Eur. J. Org. Chem. 2019, 2019, 2010–2019.
[CrossRef]
23. Gant, T.G. Using deuterium in drug discovery: Leaving the label in the drug. J. Med. Chem. 2014, 57,
3595–3611. [CrossRef]
24. Schmidt, C. First deuterated drug approved. Nat. Biotechnol. 2017, 35, 493–494. [CrossRef] [PubMed]
25. Ariza, X.; Asins, G.; Garcia, J.; Hegardt, F.G.; Makowski, K.; Serra, D.; Velascoa, J. Preparation of
aldehydes by base-catalyzed exchange reactions. J. Label. Compd. Radiopharm. 2010, 53, 556–558. [CrossRef]
26. Solladi , G.; Matloubi-Moghadam, F. Asymmetric synthesis of five- and six-membered lactones from chiral
α-labeled
é
sulfoxides: Application to the asymmetric synthesis of insect pheromones, (R)-(+)-delta-n-hexadecanolactone
and (R)-(+)-gamma-n-dodecanolactone. J. Org. Chem. 1982, 47, 91–94. [CrossRef]
27. Wheeler, J.W.; Happ, G.M.; Araujo, J.; Pasteels, J.M. γ-Dodecalactone from rove beetles. Tetrahedron Lett.
1972, 46, 4635–4638. [CrossRef]
28. Bittencourt, M.L.F.; Ribeiro, P.R.; Franco, R.L.P.; Hilhorst, H.W.M.; De Castro, R.D.; Fernandez, L.G. Metabolite
profiling, antioxidant and antibacterial activities of Brazilian propolis: Use of correlation and multivariate
analyses to identify potential bioactive compounds. Food Res. Int. 2015, 76, 449–457. [CrossRef]
29. Yore, M.M.; Syed, I.; Moraes-Vieira, P.M.; Zhang, T.; Herman, M.A.; Homan, E.A.; Patel, R.T.; Lee, J.;
Chen, S.; Peroni, O.D.; et al. Discovery of a class of endogenous mammalian lipids with anti-diabetic and
anti-inflammatory effects. Cell 2014, 159, 318–332. [CrossRef]
30. Moraes-Vieira1, P.M.; Saghatelian, A.; Kahn, B.B. GLUT4 Expression in adipocytes regulates de novo
lipogenesis and levels of a novel class of lipids with antidiabetic and anti-inflammatory effects. Diabetes 2016
,
65, 1808–1815. [CrossRef]
31. Kuda, M.; Brezinova, M.; Rombaldova, B.; Slavikova, M.; Posta, P.; Beier, P.; Janovska, J.; Veleba, J.;
Kopecky, J., Jr.; Kudova, E.; et al. Docosahexaenoic acid-derived fatty acid esters of hydroxy fatty acids
(FAHFAs) with anti-inflammatory properties. Diabetes 2016, 65, 2580–2590. [CrossRef]
32. Nelson, A.T.; Kolar, M.J.; Chu, Q.; Syed, I.; Kahn, B.B.; Saghatelian, A.; Siegel, D. Stereochemistry of
endogenous palmitic acid ester of 9-hydroxystearic acid and relevance of absolute configuration to regulation.
J. Am. Chem. Soc. 2017, 139, 4943–4947. [CrossRef] [PubMed]

Molecules 2019, 24, 2081
13 of 13
33. Pflimlin, E.; Bielohuby, M.; Korn, M.; Breitschopf, K.; Löhn, M.; Wohlfart, P.; Konkar, A.; Podeschwa, M.;
Bärenz, F.; Pfenninger, A.; et al. Acute and repeated treatment with 5-PAHSA or 9-PAHSA isomers does not
improve glucose control in mice. Cell Metab. 2018, 28, 217–227. [CrossRef] [PubMed]
34. Savle, P.S.; Lamoreaux, M.J.; Berry, J.F.; Gandour, R.D. A convenient resolution of long-chain alkyl epoxides
with Jacobsen’s salen(Co)III(OAc) catalysts. Tetrahedron: Asymmetry 1998, 11, 1843–1846. [CrossRef]
35. Harbindu, A.; Kumar, P. Synthesis of aculeatins A and B via iterative hydrolytic kinetic resolution. Synthesis
2010, 1479–1484.
36. Hubieki, M.P.; Gandour, R.D.; Ashendel, C.L. Synthesis of optically pure cyclic lipoidal ammonium salts and
evaluation of inhibition of protein kinase C. J. Org. Chem. 1996, 61, 9379–9384. [CrossRef]
37. Matsumoto, K.; Usuda, K.; Okabe, H.; Hashimoto, M.; Shimada, Y. Synthesis of optically active heterocyclic
compounds via deracemization of 1,2-diol monotosylate derivatives bearing a long aliphatic chain by a
combination of enzymatic hydrolysis with Mitsunobu inversion. Tetrahedron: Asymmetry 2013, 24, 108–115.
[CrossRef]
38. Jacoby, C.; Braekman, J.-C.; Daloze, D. Asymmetric synthesis of (2R)- and (2S)- 2-iodohexadecanal, natural
inhibitors of the thyroid gland metabolism. Tetrahedron 1996, 52, 10473–10484. [CrossRef]
39. Kumar, S.C.; Sreedhar, E.; Venkateswar, R.; Suresh, B.; Rao, J.M. A simple and efficient enantioselective
route to 2, 6-disubstituted piperidines: Synthesis of (2R, 6S)-isosolenopsin A and (2S, 6R)-isosolenopsin.
Tetrahedron: Asymmetry 2009, 20, 1160–1163. [CrossRef]
40. Boga, C.; Drioli, S.; Forzato, C.; Micheletti, G.; Nitti, P.; Prati, F. An easy route to enantiomerically enriched 7-
and 8-hydroxy-stearic acids by olefin-metathesis-based approach. Synlett 2016, 27, 1354–1358.
41. Wetzel, I.; Krauss, J.; Bracher, F. Enantiodivergent chemoenzymatic synthesis of (S)- and (R)-(Z)-9-dodecyl-
4,5,8,9-tetrahydro-3H-oxonin-2-one as analogues of topsentolides. Lett. Org. Chem. 2012, 9, 169–174. [CrossRef]
42. Padhi, B.; Reddy, G.S.; Mohapatra, D.K. Total synthesis of tetraketide and cryptorigidifoliol I via a sequential
allylation strategy. J. Nat. Prod. 2016, 79, 2788–2796. [CrossRef] [PubMed]
43. Perez, F.; Waldeck, A.R.; Krische, M.J. Total synthesis of cryptocaryol A via enantioselective iridium catalyzed
alcohol C-H allylation. Angew. Chem. Int. Ed. 2016, 55, 5049–5052. [CrossRef]
4
44. Tremblay, A.E.; Whittle, E.; Buist, P.H.; Shanklin, J. Stereochemistry of
∆
dehydrogenation catalyzed by an
ivy (Hedera helix) ∆9 desaturase homolog. Org. Biom. Chem. 2007, 5, 1270–1275. [CrossRef]
45. Kumar, P.; Pandey, M.; Gupta, P.; Dhavale, D.D. Organocatalytic stereoselective synthesis of passifloricin A.
Org. Biom. Chem. 2012, 10, 1820–1825. [CrossRef]
46. Hardy, P.M.; Aubrey Prout, R.; Rydon, H.N. Polypeptides. Part XXIV. Synthesis of isariic acid. J. Chem. Soc.
Perkin Trans. 1 1974, 796. [CrossRef]
47. Pirrung, M.C.; Zhang, F.; Ambadi, S.; Rao, Y.G. Total synthesis of fellutamides, lipopeptide proteasome
inhibitors. More sustainable peptide bond formation. Org. Biomol. Chem. 2016, 14, 8367–8375. [CrossRef]
48. Lammek, B. Resolution of racemic 3-hydroxypentadecanoic acid into its enantiomers and determination of
their absolute configuration. Roczn. Chem. 1976, 50, 997. [CrossRef]
49. Skogh, M. The higher normal chain DL-beta-hydroxy acids-synthesis and investigation of the crystal behavior
of 17 homologous acids with 8 to 24 carbon atoms. Acta Chem. Scand. 1952, 6, 809–817. [CrossRef]
50. Ansari, A.A.; Osman, S.M. Reaction of hydrogen bromide with diols of long chain α,β-unsaturated acids.
J. Am. Oil Chem. Soc. 1976, 53, 118–121. [CrossRef]
51. Negelmann, L.; Pisch, S.; Bornscheuer, U.; Schmid, R.D. Properties of unusual phospholipids. III: Synthesis,
monolayer investigations and DSC studies of hydroxy octadeca(e)noic acids and diacylglycerophosphocholines
derived therefrom. Chem. Phys. Lipids 1997, 90, 117–134. [CrossRef]
52. Goossen, L.J.; Ohlmann, D.M.; Dierker, M. Silver triflate-catalysed synthesis of γ-lactones from fatty acids.
Green Chem. 2010, 12, 197–200. [CrossRef]
Sample Availability: Samples of the compounds are available from the authors.
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