Synthesis of highly enantioenriched hydroxy- and dihydroxy-fatty esters: Substrate precursors for cytochrome P450BioI

Article abstract of DOI:10.1016/j.tetasy.2011.08.027

A series of highly enantioenriched hydroxy- and dihydroxy-fatty esters were required as part of our ongoing investigation into cytochrome P450 _BioI. This mediates the biosynthesis of pimelic acid via C-C bond cleavage of long chain fatty acids within Bacillus subtilis. Herein we report the synthesis of various stereoisomers of methyl 7-hydroxytetradecanoate, methyl 8-hydroxytetradecanoate, and methyl 7,8-dihydroxytetradecanoate in highly enantioenriched form, using a combination of asymmetric synthesis and a preparative enantioselective HPLC is reported.

Full text of DOI:10.1016/j.tetasy.2011.08.027

Tetrahedron: Asymmetry 22 (2011) 1709–1719
Contents lists available at SciVerse ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of highly enantioenriched hydroxy- and dihydroxy-fatty esters:
substrate precursors for cytochrome P450BioI
⇑
⇑
Arti A. Singh, Siti N. A. Zulkifli, Michaela Meyns, Patricia Y. Hayes , James J. De Voss
School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane 4072, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of highly enantioenriched hydroxy- and dihydroxy-fatty esters were required as part of our ongo-
ing investigation into cytochrome P450BioI. This mediates the biosynthesis of pimelic acid via C–C bond
cleavage of long chain fatty acids within Bacillus subtilis. Herein we report the synthesis of various ster-
eoisomers of methyl 7-hydroxytetradecanoate, methyl 8-hydroxytetradecanoate, and methyl 7,8-
dihydroxytetradecanoate in highly enantioenriched form, using a combination of asymmetric synthesis
and a preparative enantioselective HPLC is reported.
Received 12 August 2011
Accepted 25 August 2011
Available online 1 November 2011
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
cific production of pimelic acid,9,10 whereas the oxidation of free
fatty acids primarily produced a range of subterminally (
x
x-1 to
Cytochromes P450 (P450s or CYPs) are a superfamily of oxida-
tive haemoproteins that catalyse a wide variety of oxidative trans-
formations,1 including hydroxylation at unactivated carbon
centres2,3 and oxidative C–C bond cleavage reactions.4–8 P450BioI
(CYP107H1) from Bacillus subtilis is the first prokaryotic P450
known to catalyse an oxidative C–C bond cleavage.9 It mediates
the hydroxylation and C–C cleavage of long chain fatty acids to
produce pimelic acid (heptanedioic acid), an important intermedi-
ate in the biosynthesis of biotin (Vitamin H).5,9
To investigate the C–C bond cleavage catalysed by P450BioI, a
series of hydroxy- and dihydroxytetradecanoic acids 1–3 (Fig. 1)
were synthesised and incubated with a catalytically active P450BioI
system.5 The enzyme catalysed the oxidation of 7-hydroxytetra-
decanoic acid 1, but not that of 8-hydroxytetradecanoic acid 2,
resulting in pimelic acid production, while processing of 7,8-
threo-dihydroxytetradecanoic acid threo-3 resulted in a greater
production of pimelic acid compared to erythro-3. Probing the ste-
reoselectivity of these transformations required the synthesis of
enantioenriched samples of both 1 and threo-3. P450BioI processed
alcohol (S)-1 and the corresponding diol (7R,8R)-3 preferentially to
pimelic acid over the corresponding enantiomers, but low selectiv-
ity was observed, with (R)-1 and (7S,8S)-3 still being good sub-
strates. It was suggested that this lack of selectivity was because
-5) hydroxylated fatty acids.11 This strongly suggested that
acyl-ACPs rather than free fatty acids themselves are the natural
substrates for P450BioI. Recently-determined X-ray crystal struc-
tures of a number of P450BioI-acyl-ACP complexes support this
hypothesis and show that the fatty acid chain is oriented in a U
shape within the enzyme’s active site, with C-7 and C-8 positioned
closest to the haem iron.10,12 These structures also indicate that
both the pro-S and pro-R hydrogen atoms at C-7 and C-8 are well
positioned for oxygen insertion,10,12 suggesting that there may still
be low stereoselectivity observed between the enantiomers of
ACP-bound substrates, as previously observed with free hydroxy-
and dihydroxyacid substrates.5
We wish to explore the stereoselectivity of the C–C bond cleav-
age catalysed by P450BioI but with ACP-bound hydroxy- and dihy-
droxy-fatty acids as substrates. Thus, we require highly
enantioenriched samples of methyl 7-hydroxytetradecanoate 4,
methyl 8-hydroxytetradecanoate 5, 7,8-threo-dihydroxytetrade-
canoate threo-6 and 7,8-erythro-dihydroxytetradecanoate erythro-
6. We had previously synthesised enantioenriched samples of 4
and threo-6 but now sought more efficient routes to larger quanti-
ties of all of the stereoisomers of 4–6. These would be required for
the production of acyl-ACPs and subsequent biochemical and en-
zyme co-crystallisation studies. Herein we report the synthesis of
the enantiomers of the hydroxyesters 4 and 5 utilising preparative
enantioselective HPLC, and the enantioselective synthesis of threo
dihydroxyesters (7S,8S)-6 and (7R,8R)-6 by a shorter and less
demanding route than that reported previously.5 Additionally, an
analogous synthesis of the enantiomers of erythro-6 [(7R,8S)-6
and (7S,8R)-6] is detailed, which utilises (S)-methoxyphenylacetic
acid (MPA) ester derivatisation to facilitate both enantiomer sepa-
ration and the determination of the absolute configuration.
the free fatty acids were not the natural substrates for P450BioI
.
Acyl carrier protein-bound fatty acids (acyl-ACP) have also been
isolated in complex with P450BioI when it was heterologously
expressed.9 Enzymic oxidation of such complexes led to the spe-
⇑
Corresponding authors. Tel.: +61 7 3365 3825; fax: + 61 7 3365 4299 (J.J.D.V.).
E-mail addresses: hayesp@uq.edu.au (P.Y. Hayes), j.devoss@uq.edu.au (J.J. De
Voss).
0957-4166/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2011.08.027

1710
A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
O
O
OH
reduced with NaBH4 to the racemic hydroxyester rac-7 (83% yield).
A practical resolution of 7 by enantioselective HPLC employing a
wide range of columns and conditions proved unsuccessful, how-
ever, enantiomeric separation on a preparative scale (300 mg)
was achieved via enantioselective preparative HPLC (Chiralpak
OJ-H column) after derivatisation of rac-7 to its benzoate rac-12.
This process yielded (R)-12 and (S)-12 in 33% and 35%, respectively
(Scheme 1). The absolute configurations and enantiomeric ex-
cesses (ee) of the enantiomers of 12 were determined by enantio-
selective HPLC comparison with synthetic, enantioenriched (R)-12
(66% ee). Standard (R)-12 was synthesised by asymmetric reduc-
tion13 of the acetylenic ketone moiety of ketoester 11 using (9R)-
CBS-borane to afford the corresponding (R)-configured acetylenic
hydroxyester (R)-7 (60% yield), which was then converted to the
corresponding benzoate. Enantiomeric excesses of 96% and 88%
were determined for the HPLC separated (R)-12 and (S)-12, respec-
tively (Fig. 2). Removal of the benzoate groups from both (R)-12
and (S)-12 using sodium hydroxide in methanol, followed by cata-
lytic hydrogenation (H2, Pd/BaSO4, hexane), afforded the target,
saturated hydroxyesters (R)-5 and (S)-5 in good yields.
RO
RO
1 R = H ,4 R = CH3
OH
2 R = H, 5 R = CH3
O
OH
(R)
(R)
RO
OH
(7R,8R)-3 R = H, (7R,8R)-6 R = CH3
threo
O
OH
(S)
RO
(S)
OH
(7S,8S)-3 R = H, (7S,8S)-6 R = CH3
O
OH
(S)
RO
(R)
OH
(7R,8S)-3 R = H, (7R,8S)-6 R = CH3
erythro
O
OH
(R)
RO
(S)
OH
(7S,8R)-3 R = H, (7S,8R)-6 R = CH3
Figure 1. Synthesised hydroxy- and dihydroxy-fatty esters and their acid
analogues.
2. Results and discussion
2.1. Synthesis of hydroxy-fatty esters: (R)- and (S)-methyl 8-
hydroxytetradecanoates (R)-5 and (S)-5, and (R)- and (S)-methyl
7-hydroxytetradecanoates (R)-4 and (S)-4
Since we wished to access both enantiomers of the hydroxy-
fatty esters 4 and 5, a synthetic route that employed resolution
at a late stage was attractive. A number of methods to produce
these structurally simple molecules can be envisioned but we
wished to employ propargylic alcohols such as 7 (Scheme 1) as
intermediates. Such molecules can be generated in the enantioen-
riched form via CBS-borane reduction of the corresponding ynones
in a reaction that proceeds with predictable enantioselectivity.13
Thus, standards would be available for assigning the absolute con-
figuration of the two enantiomeric series produced via resolution.
Additionally, our previous work had shown that the enantiomers of
compounds such as 7 were amenable to analysis via enantioselec-
tive chromatography.5
Figure 2. Enantioselective HPLC traces of rac-12, (R)-12 (96% ee) and (S)-12 (88%
ee) following preparative separation, and synthetically (R)-enriched standard (R)-12
(66% ee). Chiralpak OJ-H column, 2% isopropanol in hexane, flow rate 0.5 mL minꢀ1
,
UV detector 254 nm, retention times: (R)-12 (+)-enantiomer, 15.6 min, (S)-12 (ꢀ)-
enantiomer, 16.8 min.
A strategy analogous to that employed for the synthesis of (R)-5
and (S)-5 was used to access the enantiomers of methyl 7-hydrox-
ytetradecanoate 4. The key intermediate, methyl 7-hydroxytetra-
dec-5-ynoate 13, was available starting from octanal and THP
protected hex-5-yn-1-ol as reported previously.5 As with methyl
8-hydroxytetradec-5-ynoate 7, all attempts to separate the
enantiomers of 13 by preparative enantioselective HPLC were
unsuccessful, hence rac-13 was converted to the corresponding
benzoate rac-14 (Scheme 2). Racemic 14 was subjected to prepara-
The synthesis of (R)-5 and (S)-5 began with the addition of the
anion of THP-protected hept-6-yn-1-ol14 8 (generated by reaction
with n-BuLi) to heptanal, which afforded the mono-protected diol
rac-9 in 87% yield (Scheme 1). Standard transformations then affor-
ded ketoester 11 in 73% yield over 3 steps, which was subsequently

A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
1711
O
O
a
RO
c
O
O
THPO
d
3
3
3
3
4
4
4
OH
O
OH
8
11
rac-7
rac-9 R = THP
rac-10 R = H
b
O
O
O
e
f
O
O
O
+
3
3
3
(S)
(R)
4
4
4
OBz
OR
OR
rac-12
(R)-12 R = Bz
(R)-7 R = H
(S)-12 R = Bz
(S)-7 R = H
g
g
h
h
O
O
(R)
(S)
O
O
3
4
3
4
OH
OH
(R)-5
(S)-5
Scheme 1. Synthesis of (R)-5 and (S)-5. Reagents and conditions: (a) (i) n-BuLi, THF, ꢀ40 °C, N2; (ii) heptanal, ꢀ40 °C to room temperature, N2, 87%; (b) p-TsOH, MeOH, room
temperature, 90%; (c) (i) Jones’ reagent, acetone, 0 °C to room temperature;(ii) CH2N2, MeOH, 0 °C to room temperature, 93% over two steps; (d) NaBH4, MeOH, 0 °C, 99%; (e)
BzCl, CH2Cl2, pyridine, 65%; (f) Preparative enantioselective HPLC separation (Chiralpak OJ-H column, 1% isopropanol in hexane, flow rate 10 mL minꢀ1, UV detector 254 nm),
(R)-12 (+)-enantiomer, retention time 18.3 min, 35% yield, 96% ee, (S)-12 (ꢀ)-enantiomer, retention time 21.1 min, 33% yield, 88% ee; (g) NaOH, MeOH, room temperature,
(R)-7 69%, (S)-7 64%; (h) H2, 5% Pd/BaSO4, hexane, room temperature, (R)-5 80%, (S)-5 62%.
tive enantioselective HPLC (Chiralpak OJ-H column) to afford enan-
tiomerically pure (R)-(+)-14 (43% yield) and (S)-(ꢀ)-14 (35% yield).
Hydroxyesters (R)-(ꢀ)-4 and (S)-(+)-4 were then obtained from
(R)-14 and (S)-14, respectively, following benzoate hydrolysis
and catalytic hydrogenation. The absolute stereochemistry of the
enantiomers of 4 was assigned by comparing their specific rota-
tions with those of the enantioenriched (R)-(ꢀ)-4 (68% ee) and
(S)-(+)-4 (74% ee) produced via asymmetric synthesis previously.5
These results also confirmed the configurations of the enantiomers
of 14 and were in accordance with those expected from their HPLC
elution order: the (R)-enantiomer of both 12 and 14 elutes first.
It is worth noting that, despite the fact 4 and 5 are chiral only
because of the differences in substituents some six bonds removed
from the stereogenic centre, they have small but characteristic spe-
cific rotations; the (R)-isomer is the (ꢀ)-enantiomer in both cases.
Additionally, HPLC resolution of a racemate for the production of
OH
OBz
O
a
4
O
4
O
O
3
3
rac-13
rac-14
OR
OR
O
O
b
(R)
(S)
4
+
4
O
O
3
3
(R)-14 R = Bz
(R)-13 R = H
(S)-14 R = Bz
(S)-13 R = H
c
c
d
d
O
OH
O
OH
O
(R)
(S)
O
4
3
4
3
(R)-4
(S)-4
Scheme 2. Synthesis of (R)-4 and (S)-4. Reagents and conditions: (a) BzCl, CH2Cl2, pyridine, room temperature, 64%; (b) preparative enantioselective HPLC separation (Chiralpak
OJ-H column, 2% isopropanol in hexane, flow rate 10 mL minꢀ1, UV detector 254 nm), (R)-14 (+)-enantiomer, retention time 14.9 min, 43% yield, >99% ee, (S)-14 (ꢀ)-enantiomer,
retention time 17.4 min, 35% yield, >99% ee; (c) NaOH, MeOH, room temperature; (d) H2, 5% Pd/BaSO4, hexane, room temperature, (R)-4 40%, (S)-4 35% over two steps.

1712
A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
enantioenriched 4 and 5 compared favourably to an asymmetric
synthesis utilising CBS-borane; higher ee’s were achieved (88–
100% vs 68–74%) and the operationally difficult CBS-borane reduc-
tion was avoided.
Reduction (Li/NH3) of alkyne 15 afforded the (E)-alkene (E)-18
in 83% yield (Scheme 4). Acid catalysed cleavage of the THP moiety,
followed by Jones oxidation of alcohol (E)-19 and esterification of
acid (E)-20 afforded the methyl ester (E)-16 in 78% yield over three
steps. Dihydroxylation of (E)-16 with either AD-mix-a or AD-mix-b
2.2. Synthesis of the threo and erythro enantiomers of methyl
7,8-dihydroxytetradecanoate, (7S,8S)-6, (7R,8R)-6, (7R,8S)-6 and
(7S,8R)-6
under standard SAD conditions provided the desired 7,8-threo-
dihydroxyesters (7S,8S)-6 and (7R,8R)-6 in 81% and 75% yields,
respectively. Based upon the Sharpless predictive model,15 the
AD-mix-
a would provide the enriched (S,S)-enantiomer and AD-
The previously reported5 synthesis of (7S,8S)-6 and (7R,8R)-6
utilised non-racemic diethyl tartarates as starting materials, with
the production of the enantiomers requiring 12 steps for each.
We envisioned a much more efficient synthesis by making use of
the key alkyne 15. This could be stereoselectively reduced to either
an (E)- or (Z)-alkene that, upon osmium catalysed dihydroxylation,
would yield the corresponding threo and erythro-diols (threo-6 and
erythro-6), respectively. Sharpless asymmetric dihydroxylation
(SAD)15 of the achiral alkenes (E)-16 and (Z)-16 would provide
the opportunity for enantioselective introduction of chirality.
(E)-Alkenes, such as (E)-16, are known to readily undergo SAD
reactions to afford vicinal diols with threo stereochemistry and
high ee’s, while SAD reactions of (Z)-alkenes [e.g. (Z)-16] provides
erythro vicinal diols, albeit with lower ee’s.
mix-b the (R,R)-enantiomer. This prediction was confirmed by
comparison of the specific rotations of the compounds obtained
here with those of (7S,8S)-6 and (7R,8R)-6 synthesised previously
from chiral, non-racemic tartrate starting materials.5 Enantioselec-
tive HPLC analysis (Chiralpak AD-H column) revealed an ee >99%
for both (7S,8S)-6 (from AD-mix-a) and (7R,8R)-6 (from AD-mix-
b). This route thus provides highly enantioenriched samples of
both enantiomers of threo-6 in nine synthetic steps as compared
to 24 steps in the synthesis reported previously.5
The synthesis of the erythro-dihydroxyesters (7R,8S)-6 and
(7S,8R)-6 similarly utilised alkyne 15, but with catalytic hydroge-
nation (Lindlar’s catalyst) affording (Z)-18 in quantitative yield
(Scheme 5). GC/MS and NMR analysis revealed the presence of a
small amount (ꢁ10%) of the corresponding, chromatographically
inseparable (E)-18. This was therefore carried forward through
the synthesis for separation at a later stage. The desired (Z)-methyl
ester (Z)-16 was obtained in high yield following standard THP-
deprotection of (Z)-18 (94% yield), Jones oxidation of alcohol (Z)-
19 (92%), and esterification of acid (Z)-20 (96%).
The key intermediate 15 (Scheme 3) was available in good yield
in three steps from commercially available starting materials.
Deprotonation of 1-octyne with n-BuLi, and subsequent reaction
with THP-protected 6-bromo-1-hexanol16 17 in the presence of
HMPA, afforded the desired product 15 in 81% yield.
Dihydroxylation of (E)-alkenes under SAD conditions usually
occurs more quickly than that of the corresponding (Z)-alkenes.
Thus, oxidation of the mixture of (Z)- and (E)-16 (ꢁ10:1) at this
a
Br
Br
HO
THPO
3
3
17
stage with 0.15 equiv of AD-mix-a (26 h) allowed dihydroxylation
of the ꢁ10% of (E)-alkene impurity present, while leaving the
majority of (Z)-16 unreacted. Purification of the unreacted alkene
(Z)-16 by column chromatography provided geometrically pure
(Z)-16. Subsequent dihydroxylation on geometrically pure (Z)-16
b
4
THPO
4
3
15
under standard SAD conditions (AD-mix-a, 210 h) afforded ery-
17
thro-6 in 97% yield (Scheme 6). Since the oxidation of (Z)-alkenes
with the commercially available SAD reagent premixes is known
to occur with less enantioselectivity than of the corresponding
(E)-alkenes,15 it was not expected that this step would proceed
Scheme 3. Synthesis of bromide 17 and alkyne 15. Reagents and conditions: (a)
3,4-dihydro-2H-pyran, p-TsOH, CH2Cl2, 0 °C to room temperature, N2, 83%; (b) (i) n-
BuLi, THF, ꢀ40 °C, N2; (ii) HMPA, bromide 17, ꢀ40 °C to room temperature, N2, 81%.
(E)
a
RO
4
4
3
THPO
3
(E)-18 R = THP
(E)-19 R = H
15
b
O
OH
(S)
O
O
(S)
e
3
4
O
OH
(E)
c
(7S,8S)-6
RO
4
3
O
OH
f
(E)-20 R = H
(E)-16 R = CH3
(R)
d
(R)
4
3
OH
(7R,8R)-6
Scheme 4. Synthesis of (7S,8S)-6 and (7R,8R)-6 from alkyne 15. Reagents and conditions: (a) Li (s)/NH3 (l), t-BuOH/THF (3:5), ꢀ78 °C, 83%; (b) p-TsOH, MeOH, room
temperature, 95%; (c) Jones’ reagent, acetone, 0 °C to room temperature, 83%; (d) CH2N2, MeOH, 0 °C to room temperature, 99%; (e) AD-mix-a, MeSO2NH2, t-BuOH/H2O (1:1),
0–4 °C, 81%, >99% ee; (f) AD-mix-b, MeSO2NH2, t-BuOH/H2O (1:1), 0–4 °C, 75%, >99% ee (Chiralpak AD-H column, 2% isopropanol in hexane, flow rate 0.5 mL minꢀ1, UV
detector 215 nm, retention times: (7S,8S)-6 16. 9 min, (7R,8R)-6 16.0 min).

A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
1713
(Z)
enantiomers of erythro-6 into their bis-methoxyphenylacetic acid
ester derivatives to at once facilitate both analytical and prepara-
tive separation, as well as to allow the determination of their abso-
lute configurations (Mosher’s analysis).
a
RO
3
4
4
THPO
3
(Z)-18 R = THP
(Z)-19 R = H
15
b
Thus the dihydroxyester erythro-6 obtained from the dihydr-
oxylation of (Z)-16 was reacted with (S)-methoxyphenylacetic acid
to afford the crude diastereomeric bis-(S)-methoxyphenylacetic
acid esters erythro-21 (Scheme 6). Enantioselective HPLC analysis
(Chiralpak AD-H column), unsurprisingly, revealed a low de of
10%, reflecting a 10% ee for the dihydroxylation of (Z)-16. The dia-
stereomeric bis-(S)-methoxyphenylacetic acid esters were success-
fully separated by preparative enantioselective HPLC to afford pure
(7R,8S)-21 and (7S,8R)-21 in 32% and 42% yields, respectively
(>99% de and ee following separation). Base-catalysed methanoly-
sis of the (S)-methoxyphenylacetic acid esters (7R,8S)-21 and
(7S,8R)-21 provided the corresponding enantiomerically pure
dihydroxy-fatty esters (7R,8S)-6 (65%) and (7S,8R)-6 (58% yield;
Scheme 6).
O
(Z)
c
RO
3
4
(Z)-20 R = H
(Z)-16 R = CH3
d
Scheme 5. Synthesis of (Z)-16 from alkyne 15. Reagents and conditions: (a) H2,
Lindlar’s catalyst (5% Pd/CaCO3 poisoned with lead), EtOAc, room temperature,
quantitative; (b) p-TsOH, MeOH, room temperature, 94%; (c) Jones reagent, acetone,
0 °C to room temperature, 92%; (d) CH2N2, MeOH, 0 °C to room temperature, 96%.
with high stereoselectivity but it was hoped that preparative enan-
tioselective HPLC would provide the pure enantiomers. However,
all attempts to separate the erythro enantiomers (7S,8R)-6 and
(7S,8R)-6 were unsuccessful. It was thus decided to convert the
The absolute configuration at the 7- and 8-positions of both
(7R,8S)-21 and (7S,8R)-21 was determined by NMR spectroscopy.
The signals in the 1H NMR spectra of (7R,8S)-21 and (7S,8R)-21 ob-
Ph
Ph
H
H
O
O
O
O
OH
(S)
(S)
(S)
(R)
O
O
O
O
O
O
O
O
O
4
4
3
3
(Z)
OH
(R)
(S)
a
b,c
(R)
(S)
O
O
O
+
4
+
3
4
3
3
4
O
H
O
H
OH
O
O
(Z)-16
(R)
(S)
(S)
(S)
O
O
Ph
Ph
OH
(7R,8S)-21
(7S,8R)-21
erythro-6
d
d
O
OH
O
OH
(R)
(S)
(R)
O
(S)
O
3
4
4
3
OH
OH
(7R,8S)-6
(7S,8R)-6
Scheme 6. Synthesis of (7R,8S)-6 and (7S,8R)-6 from (Z)-16. Reagents and conditions: (a) AD-mix-a, MeSO2NH2, t-BuOH/H2O (1:1), 0–4 °C, 97%; (b) (S)-methoxyphenylacetic
acid, DCC, DMAP, CH2Cl2; (c) preparative enantioselective HPLC separation (Chiralpak AD-H column, 10% isopropanol in hexane, flow rate 10 mL minꢀ1, UV detector 254 nm),
de 10%; (7R,8S)-21 retention time 22.8 min, 32%, (7S,8R)-21 retention time 28.6 min, 42% (both >99% de and ee); (d) NaOH, MeOH, room temperature, (7R,8S)-6 65%, (7S,8R)-6
58%.
Figure 3. Partial 1H NMR spectra (C6D6, 400 MHz) and diagnostics
Dd
RS values for bis-(S)-methoxyphenylacetic acid esters (7R,8S)-21 and (7S,8R)-21. The signals for H-7 and
H-8 were assigned from selective 1D TOCSY experiments.

1714
A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
tained in C6D6 (Fig. 3) were better resolved than the signals in the
corresponding spectra obtained in CDCl3; thus the data obtained in
C6D6 were used for the stereochemical analysis. Selective 1D TOC-
SY experiments were used to assign the signals for H-7 and H-8 in
both (7R,8S)-21 and (7S,8R)-21. Irradiation of the signal corre-
sponding to the methylene group adjacent to the methyl ester
(H2-2) for (7R,8S)-21 revealed that the signal at dH 4.93 ppm corre-
sponded to H-7, whereas H-7 was found to resonate at dH 5.35 ppm
for (7S,8R)-21. This was confirmed by irradiation of the signal cor-
responding to the terminal methyl group (H3-14) for each isomer,
which indicated the signals corresponding to H-8: dH 5.39 for
(7R,8S)-21 and dH 4.97 for (7S,8R)-21.
vanillin and 2.5 mL concentrated H2SO4 dissolved in 250 mL EtOH).
1H and 13C NMR spectra were recorded on either a Bruker AMX400or
Bruker AV500 spectrometer as indicated. 1H and 13C signals are
recorded in parts per million (ppm) on the d scale, with the residual
solvent peaks (CDCl3: dH 7.24 and dC 77.0; C6D6: dH 7.15 and dC 128.0)
as internal references. GC/MS analyses were performed on a Shima-
dzu GCMS QP5000 or QP5050 gas chromatograph mass spectrome-
ter, operating at 70 eV, connected to a GC-17A gas chromatograph
fitted with a DB-5 column (30 m, internal diameter 0.25 mm, J&W
Scientific). Standard GC/MS programme: split mode; column flow
1.0 mL minꢀ1; total flow 102.2 mL minꢀ1; injector 250 °C; detector
250 °C; oven 100 °C (1.0 min equilibration) held for 2.0 min, ramp
16 °C minꢀ1 to 250 °C and held for 24.0 min (total programme time
35.4 min). Melting points were measured on a Buchi Dr. Tottoli
apparatus and are uncorrected. High resolution mass spectra were
recorded in positive ion ESI mode on a Bruker micrOTOFQ spectrom-
eter. Elemental microanalyses were performed by the Microanalyt-
ical Service, School of Chemistry and Molecular Biosciences, at the
University of Queensland. Optical rotations were measured at the
sodium D line (589 nm) at ambient temperature using a 1 mL quartz
cell with a 10 cm path length, using a Jasco P-2000 polarimeter.
Analytical and preparative enantioselective HPLC was performed
on an Agilent 1200 Series Liquid Chromatograph System equipped
with a UV detector and an ALP (Advanced Laser Polarimeter,
PDR-Chiral Inc.) using Chiralpak OJ-H or AD-H columns (20 ꢂ
250 mm or 4.6 ꢂ 250 mm, Daicel Chemical Industries, Ltd.) as
indicated.
Diagnostic
D
dRS values were then calculated17,18 from the 1H
chemical shift values observed for these four important signals
(Fig. 3). These calculated values were then used to assign the abso-
lute configuration at the 7- and 8-positions of both (7R,8S)-21 and
(7S,8R)-21, based upon the model developed by Seco et al.17,18 for
determining the absolute configuration of 1,n-diols from the chem-
ical shifts of their bis-methoxyphenylacetic acid ester derivatives.
Despite the requirement of chemical derivatisation, subsequent
deprotection and preparative enantioselective HPLC separation in
this synthesis of the enantiomers of erythro-6, the route has much
to recommend it. It provides both (7R,8S)-6 and (7S,8R)-6 enantio-
merically pure and in preparatively useful quantities (ꢁ10 mg
each) in only ten synthetic steps. In addition, the use of the bis-
(S)-methoxyphenylacetic acid derivatives (7R,8R)-21 and
(7S,8S)-21 allowed the direct determination of the absolute stereo-
chemistry of each enantiomer.
4.2. Synthesis of (R)- and (S)-methyl 8-hydroxytetradecanoates
(R)-5 and (S)-5
3. Conclusions
4.2.1. rac-14-(Tetrahydro-2H-pyran-2-yloxy)tetradec-8-yn-7-ol
rac-9
Using a combination of asymmetric synthesis and preparative
enantioselective HPLC, we have successfully synthesised a series
of isomeric hydroxy- and dihydroxy-fatty esters with demon-
strated high levels of enantioenrichment in preparatively useful
amounts. Both 7-hydroxy and 8-hydroxytetradecanoates 1 and 2
have been reported from natural sources; the former from a variety
of butterflies19 and the latter from plant leaves.20 However, the ste-
reochemistry of these naturally occurring compounds has not been
investigated and the data reported here should help facilitate fu-
ture work. Indeed, the positive specific rotation observed for both
(S)-4 and (S)-5 aligns with a seemingly general trend for the (S)-
enantiomers of hydroxy-fatty acids. Additionally, all of the com-
pounds reported here will be useful in our future investigations
of the stereoselectivity of the C–C bond cleavage process catalysed
A solution of n-BuLi (1.15 M in hexanes, 24.0 mL, 27.6 mmol)
was added dropwise to a solution of 2-(hept-6-ynyloxy)tetrahy-
dro-2H-pyran14 8 (4.00 g, 20.4 mmol) in THF (40 mL) stirred at
ꢀ40 °C under an N2 atmosphere. The solution was stirred at
ꢀ40 °C for 3 h, then freshly distilled heptanal (5.81 g, 50.8 mmol)
was added dropwise. The reaction mixture was stirred at ꢀ40 °C
for 15 min, then was allowed to warm to room temperature and
was stirred for 2 days. Saturated aqueous NH4Cl solution
(100 mL) was then added to quench the reaction, and the mixture
was extracted with Et2O (5 ꢂ 100 mL). The combined organic ex-
tract was washed with brine (100 mL), dried over anhydrous
MgSO4, filtered and concentrated in vacuo. The crude product
was purified by flash chromatography (silica gel, 10–50% EtOAc
in petroleum spirit 40–60) to afford rac-9 (5.53 g, 17.8 mmol,
87%) as a colourless oil. 1H NMR (400 MHz, CDCl3) d 0.87 (t,
J = 6.6 Hz, 3H, H3-14), 1.20–1.88 (m, 22 H), 2.22 (dt, J = 6.9,
2.0 Hz, 2H, H2-5), 3.39 (td, J = 9.6, 6.6 Hz, 1H, H-1), 3.47–3.53 (m,
1H, H-60), 3.74 (td, J = 9.6, 6.8 Hz, 1H, H-1), 3.84–3.90 (m, 1H, H-
60), 4.34 (tt, J = 6.5, 1.9 Hz, 1H, H-8), 4.57 (t, J = 3.5 Hz, 1H, H-20).
13C NMR (100 MHz, CDCl3) d 14.1 (C-14), 18.6, 19.7, 22.6, 25.2,
25.5, 28.4, 28.9, 29.2, 29.7, 30.8, 31.7, 38.2, 62.4 (C-60), 62.8 (C-8),
67.4 (C-1), 81.5 (C„C), 85.3 (C„C), 98.9 (C-20). GC/MS EI m/z (%)
209 (1), 165 (1), 141 (6), 101 (9), 85 (100), 84 (35), 67 (31), 57
(25), 55 (83), 43 (46), 41 (51). Anal. Calcd for C19H34O3: C, 73.50;
H, 11.04. Found: C, 73.13; H, 11.29. HRMS ESI calcd for C19H34NaO3
([M+Na]+Å): 333.2400. Observed: 333.2389.
by P450BioI
.
4. Experimental
4.1. General
Materials obtained commercially were of reagent grade unless
otherwise stated. Anhydrous solvents were dried according to the
established procedures and were distilled under vacuum or N2
immediately prior to use. THF was distilled off sodium-benzophe-
none ketyl. CH2Cl2 and DMSO were dried over and distilled from
CaH2. HMPA was dried and stored over CaH2. Moisture or air sensi-
tive experiments were conducted in oven-dried glassware under a
N2 or Ar atmosphere. Flash column chromatography was performed
on Silica Gel 60 (0.04–0.06 mm, 230–400 mesh, Scharlau or Merck).
TLC was performed on Kieselgel 60 F254 plates (Merck, aluminium
backed). Compounds were visualised by treatment with PMA (5%
phosphomolybdic acid in EtOH), KMnO4 (1.0 g KMnO4, 5.0 g Na2CO3
and 500 mg NaOH dissolved in 100 mL H2O), or vanillin dips (6.0 g
4.2.2. rac-Tetradec-6-yne-1,8-diol rac-10
A solution of rac-9 (4.80 g, 15.5 mmol) and p-toluenesulfonic
acid (cat., 200 mg) in MeOH (200 mL) was stirred at room temper-
ature for 2 h. Solid NaHCO3 (5.0 g) was added to quench the reac-
tion and the solvent was evaporated under reduced pressure The
residue was purified by flash chromatography (silica gel, 5–50%

A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
1715
EtOAc in petroleum spirit 40–60) to afford the diol rac-10 (3.16 g,
14.0 mmol, 90%) as a colourless oil. 1H NMR (400 MHz, CDCl3) d
0.88 (t, J = 6.9 Hz, 3H, H3-14), 1.22–1.72 (m, 16H), 2.22 (dt, J = 6.9,
2.0 Hz, 2H, H2-5), 3.65 (t, J = 6.5 Hz, 2H, H2-1), 4.33 (tt, J = 6.6,
1.8 Hz, 1H, H-8). 13C NMR (100 MHz, CDCl3) d 14.0 (C-14), 18.6,
22.6, 24.9, 25.2, 28.3, 28.9, 31.7, 32.1, 38.2, 62.7, 62.8, 81.6
(C„C), 85.1 (C„C). GC/MS EI m/z (%) 180 (3), 141 (33), 138 (12),
109 (14), 95 (61), 79 (50), 67 (70), 55 (100), 43 (94), 41 (79). Anal.
Calcd for C14H26O2: C, 74.29; H, 11.58. Found: C, 73.88; H, 11.74.
HRMS ESI calcd for C14H26NaO2 ([M+Na]+Å): 249.1825. Observed:
249.1832.
0.24 mmol) in THF (5 mL) stirred under an N2 atmosphere. After
10 min the solution was cooled to ꢀ30 °C and a borane–DMS com-
plex (5 M in Et2O, 53 lL, 0.27 mmol) was added dropwise. After
75 min, the reaction mixture was quenched by the addition of
MeOH (1 mL) and was warmed to room temperature and diluted
with Et2O (20 mL). The organic solution was washed with a 1:1
solution of 1 M aqueous NaOH and saturated aqueous NaHCO3
(4 ꢂ 20 mL), and then brine (30 mL), and then was dried over anhy-
drous MgSO4, filtered and concentrated in vacuo. The crude prod-
uct was purified by flash chromatography (silica gel, 20% EtOAc
in hexane) to afford enantioenriched (R)-7 (36 mg, 0.14 mmol,
60%) as a colourless oil. ½a D25
¼ ꢀ1:3 (c 0.95, CHCl3). This compound
ꢃ
4.2.3. Methyl 8-oxotetradec-6-ynoate 11
was spectroscopically identical to rac-7.
To a solution of rac-10 (143 mg, 0.63 mmol) in acetone (6 mL)
stirred at 0 °C was added Jones’ reagent (8 M) dropwise until the
reaction mixture remained orange in colour. The reaction mixture
was allowed to warm to room temperature with stirring over
20 min, then was quenched by the addition of H2O (20 mL). The
mixture was extracted with Et2O (4 ꢂ 10 mL) and the combined
organic extract was dried over anhydrous MgSO4, filtered and con-
centrated under reduced pressure. The crude acid was redissolved
in methanol (10 mL) and the solution was cooled to 0 °C. An ether
CH2N2 solution was added dropwise until a yellowish colour per-
sisted. The excess CH2N2 was evaporated under a stream of N2
and the solvent was removed in vacuo. The residue was purified
by flash chromatography (silica gel, 5% Et2O in hexane) to afford
11 (149 mg, 0.59 mmol, 93% over 2 steps) as a pale yellow oil. 1H
NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.9 Hz, 3H, H3-14), 1.26–1.37
(m, 8H), 1.61–1.67 (m, 2H), 1.75 (m, 2H), 2.35 (t, J = 7.3 Hz, 2H),
2.39 (t, J = 7.0 Hz, 2H), 2.52 (t, J = 7.3 Hz, 2H), 3.68 (s, 3H, RCO2CH3).
13C NMR (100 MHz, CDCl3) d 14.0 (C-14), 18.7, 22.4, 24.1, 27.1,
28.6, 29.7, 31.5, 33.4, 45.5 (C-9), 51.6 (RCO2CH3), 81.1 (C„C),
93.1 (C„C), 173.6 (C-1), 188.5 (C-8). GC/MS EI m/z (%) 221 (10),
135 (53), 108 (64), 95 (42), 79 (100), 77 (36), 67 (28), 55 (39), 43
(83), 41 (64). Anal. Calcd for C15H24O3: C, 71.39; H, 9.59. Found:
C, 71.20; H, 9.63. HRMS ESI calcd for C15H24NaO3 ([M+Na]+Å):
275.1618. Observed: 275.1623.
4.2.6. rac-14-Methoxy-14-oxotetradec-8-yn-7-yl benzoate rac-
12
Benzoyl chloride (583
lL, 5.0 mmol) was added dropwise to a
solution of rac-7 (438 mg, 1.72 mmol) and pyridine (826
l
L,
10.2 mmol) in anhydrous CH2Cl2 (30 mL) stirred at 0 °C. The reac-
tion mixture was allowed to warm to room temperature and was
stirred for 4 h, then water (5 mL) was added to quench the
reaction. The organic and aqueous layers were separated and the
aqueous solution was extracted with Et2O (3 ꢂ 20 mL). The com-
bined organic extract was dried over anhydrous MgSO4, filtered
and concentrated in vacuo. The crude product was purified by flash
chromatography (silica gel, 5% EtOAc in hexane) to afford the pure
benzoate rac-12 (400 mg, 1.12 mmol, 65%) as a colourless oil. 1H
NMR (400 MHz, CDCl3) d 0.87 (t, J = 7.0 Hz, 3H, H3-14), 1.14–1.28
(m, 6H), 1.35–1.47 (m, 4H), 1.57–1.65 (m, 2H), 1.69–1.82 (m,
2H), 2.13 (dt, J = 7.2, 1.9 Hz, 2H, H2-5), 2.41 (t, J = 7.2 Hz, 2H, H2-
2), 3.54 (s, 3H, RCO2CH3), 5.47 (tt, J = 6.5, 1.9 Hz, 1H, H-8), 7.30–
7.35 (m, 2H), 7.42–7.47 (m, 1H), 7.93–7.97 (m, 2H). 13C NMR
(100 MHz, CDCl3) d 14.0 (C-14), 18.4, 22.5, 24.1, 25.1, 27.9, 28.8,
31.7, 33.5, 35.2, 51.5 (RCO2CH3), 65.1 (C-8), 78.2 (C„C), 85.5
(C„C), 128.3 (2C), 129.7 (2C), 130.2, 132.9, 165.7 (RCO2Ph),
173.8 (C-1). GC–MS EI m/z (%) 226 (2) 105 (100), 78 (5), 77 (63),
51 (82) 50 (29), 43 (22). Anal. Calcd for C22H30O4: C, 73.71; H,
8.44. Found: C, 73.55; H, 8.73.
4.2.4. rac-Methyl 8-hydroxytetradec-6-ynoate rac-7
A solution of 11 (149 mg, 0.59 mmol) in MeOH (25 mL) was
cooled to 0 °C and then NaBH4 (88 mg, 2.33 mmol) was added por-
tion-wise. The reaction mixture was stirred at 0 °C for 2 h, then
aqueous oxalic acid solution (5%, 5 mL) was added. The MeOH
was removed by rotary evaporation and then the residue was ex-
tracted with CH2Cl2 (4 ꢂ 20 mL). The combined organic extract
was washed with saturated aqueous NaHCO3 solution (20 mL)
and brine (20 mL). The organic solution was dried over anhydrous
MgSO4, filtered and concentrated in vacuo. Purification by flash
chromatography (silica gel, 20% EtOAc in hexane) afforded rac-7
(149 mg, 0.59 mmol, 99%) as a colourless oil. 1H NMR (500 MHz,
CDCl3) d 0.88 (t, J = 7.1 Hz, 3H, H3-14), 1.23–1.35 (m, 6H), 1.38–
1.46 (m, 2H), 1.54 (m, 2H), 1.59–1.77 (m, 4H), 2.23 (dt, J = 7.0,
1.9 Hz, 2H, H2-5), 2.33 (t, J = 7.5 Hz, 2H, H2-2), 3.67 (s, 3H,
RCO2CH3), 4.33 (tt, J = 6.6, 1.9 Hz, 1H, H-8). 13C NMR (125 MHz,
CDCl3) d 14.0 (C-14), 18.4, 22.6, 24.1, 25.1, 28.0, 28.9, 31.7, 33.5,
38.2, 51.5 (RCO2CH3), 62.7 (C-8), 81.9 (C„C), 84.6 (C„C), 173.9
(C-1). GC/MS EI m/z (%) 223 (1), 169 (72), 137 (68), 109 (63), 92
(35), 81 (73), 79 (59.), 74 (31), 67 (66), 55 (70), 43 (100), 41 (98).
Anal. Calcd for C15H26O3: C, 70.83; H, 10.30. Found: C, 70.68; H,
10.49. HRMS ESI calcd for C15H26NaO3 ([M+Na]+Å): 277.1774. Ob-
served: 277.1784.
4.2.7. Analysis and preparative enantioselective HPLC
separation of rac-12
Preparative enantioselective HPLC separation (Chiralpak OJ-H
column, 1% isopropanol in hexane, flow rate 10 mL minꢀ1, UV
detector 254 nm) was performed with 1 mL injections of a 1 mg/
mL solution of rac-12. Retention times: (R)-12 [(+)-enantiomer]
18.3 min, (S)-12 [(ꢀ)-enantiomer] 21.1 min. The enantiomeric pur-
ity of each isomer following preparative separation was deter-
mined by analytical enantioselective HPLC (Chiralpak OJ-H
column, 2% isopropanol in hexane, flow rate 0.5 mL minꢀ1, UV
detector 254 nm). Retention times: (R)-12 [(+)-enantiomer]
15.0 min, (S)-12 [(ꢀ)-enantiomer] 16.0 min.
4.2.7.1. (+)-(R)-14-Methoxy-14-oxotetradec-8-yn-7-yl benzoate
(R)-12. 106 mg, 0.30 mmol, 35%, 96% ee. ½a D25
¼ þ17:3 (c 0.93,
ꢃ
CHCl3). By comparison with the enantioenriched standard (R)-12,
the observed retention time of 15.2 min indicated that the major
isomer was the (R)-enantiomer. This compound was spectroscopi-
cally identical to rac-12.
4.2.7.2. (ꢀ)-(S)-14-Methoxy-14-oxotetradec-8-yn-7-yl benzoate
(S)-12. 100 mg, 0.28 mmol, 33%, 88% ee. ½a D25
¼ ꢀ18:6 (c 0.68,
ꢃ
4.2.5. Enantioenriched (R)-Methyl 8-hydroxytetradec-6-ynoate
(R)-7
(9R)-CBS-borane (1.0 M in toluene, 0.49 mL, 0.49 mmol) was
added to a solution of methyl 8-oxotetradec-6-ynoate 11 (60 mg,
CHCl3). The observed retention time of 16.2 min indicated that
the major isomer was the (S)-enantiomer. This compound was
spectroscopically identical to rac-12.

1716
A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
4.2.8. Enantioenriched (R)-14-Methoxy-14-oxotetradec-8-yn-7-
yl benzoate (R)-12
J = 7.1, 2.1 Hz, 2H, H2-5), 2.41 (t, J = 7.7 Hz, 2H, H2-2), 3.65 (s,
3H, RCO2CH3), 5.56 (tt, J = 6.6, 1.9 Hz, 2H, H-7), 7.44–7.40 (m,
2H), 7.56–7.52 (m, 1H), 8.05–8.02 (m, 2H). 13C NMR
Following a procedure analogous to that for the synthesis of rac-
12, enantioenriched (R)-12 (15 mg, 48
from enantioenriched (R)-7 (35 mg, 138
l
mol, 30%) was synthesised
mol) and was obtained
(100 MHz, CDCl3) d 14.1 (C-14), 18.2, 22.6, 23.7, 29.1 (2C),
l
31.7, 32.7, 35.1, 51.5 (RCO2CH3), 65.0 (C-8), 78.7 (C„C), 84.8
(C„C), 128.3 (2C), 129.7 (2C), 130.2, 133.0, 165.6 (RCO2Ph),
173.5 (C-1). GC/MS EI m/z (%) 271 (3), 221 (1), 194 (1), 174
(2), 105 (100), 91 (8), 77 (30), 67 (7), 55 (19), 43 (26), 41
(32). Anal. Calcd for C22H30O4: C, 73.71; H, 8.44. Found: C,
as a colourless oil. 66% ee (Chiralpak OJ-H column, 2% isopropanol
in hexane, flow rate 0.5 mL minꢀ1, UV detector 254 nm; retention
times: major isomer (R)-12 15.6 min, minor isomer (S)-12
16.8 min). ½a 2D5
¼ þ12:5 (c 1.20, CHCl3). This compound was spec-
ꢃ
troscopically identical to rac-12.
73.88; H, 8.73. HRMS ESI calcd for
381.2042. Observed: 381.2036.
C
22H30NaO4 ([M+Na]+Å):
4.2.9. (ꢀ)-(R)-Methyl 8-hydroxytetradec-6-ynoate (R)-7
Powdered solid NaOH (80 mg, 2.0 mmol) was added to a solu-
tion of (R)-12 (106 mg, 0.30 mmol; obtained from resolution of
rac-12) in MeOH (10 mL), followed by a drop of water. The solution
was allowed to stir at room temperature overnight, and then water
was added (20 mL) and the mixture was extracted with EtOAc
(2 ꢂ 20 mL). After drying over anhydrous MgSO4, the combined or-
ganic extract was filtered and then concentrated in vacuo. The
crude product was purified by flash chromatography to afford
4.3.2. Analysis and preparative enantioselective HPLC
separation of rac-14
Preparative enantioselective HPLC separation (Chiralpak OJ-H
column, 2% isopropanol in hexane, flow rate 10 mL minꢀ1, UV
detector 254 nm) was performed with 1 mL injection of
a
5 mg/mL solution of rac-14. Retention times: (R)-14 [(+)-enantio-
mer] 14.9 min, (S)-14 [(ꢀ)-enantiomer] 17.4 min. Both enantio-
mers were obtained enantiomerically pure (>99% ee) after
preparative HPLC separation, as determined by analytical enan-
tioselective HPLC (Chiralpak OJ-H column, 2% isopropanol in hex-
ane, flow rate 0.5 mL minꢀ1, UV detector 254 nm). Retention
times: (R)-14 [(+)-enantiomer] 13.6 min, (S)-14 [(ꢀ)-enantiomer]
16.9 min.
(R)-7 (52 mg, 0.20 mmol, 69%) as a colourless oil. ½a D25
¼ ꢀ1:7 (c
ꢃ
0.46, CHCl3). This compound was spectroscopically identical to
rac-7.
4.2.10. (+)-(S)-Methyl 8-hydroxytetradec-6-ynoate (S)-7
Following a procedure analogous to that for the synthesis of (R)-
7, the enantiomeric (S)-7 (48 mg, 0.19 mmol, 64%) was synthesised
from (S)-7 (105 mg, 0.29 mmol) and was obtained as a colourless
4.3.2.1. (+)-(R)-1-Methoxy-1-oxotetradec-5-yn-7-yl benzoate
oil. ½a 2D5
¼ þ1:9 (c 0.90, CHCl3). This compound was spectroscopi-
ꢃ
(R)-14. 128 mg, 0.36 mmol, 43%, >99% ee. ½a D25
¼ þ20:4 (c 1.20,
ꢃ
cally identical to rac-7.
CHCl3). This compound was spectroscopically identical to rac-14.
4.2.11. (R)-Methyl 8-hydroxytetradecanoate (R)-5
4.3.2.2. (ꢀ)-(S)-1-Methoxy-1-oxotetradec-5-yn-7-yl benzoate
A solution of (R)-7 (52 mg, 0.20 mmol) in hexane (20 mL) was
stirred under an H2 atmosphere for 1 h in the presence of a cata-
lytic amount of 5% Pd/BaSO4. After filtration, concentration and
purification by flash chromatography (silica gel, 25% EtOAc in hex-
ane), (R)-5 (42 mg, 0.16 mmol, 80%) was obtained as a white solid
(S)-14. 106 mg, 0.30 mmol, 35%, >99% ee. ½a D25
¼ ꢀ21:7 (c 1.10,
ꢃ
CHCl3). This compound was spectroscopically identical to rac-14.
(mp 29–30 °C). ½a D25
ꢃ
¼ ꢀ1:2 (c 0.68, CHCl3). 1H NMR (400 MHz,
4.3.3. (S)-Methyl 7-hydroxytetradecanoate (S)-4
Powdered solid NaOH (80 mg, 2.0 mmol) was added to a solu-
tion of (S)-14 (106 mg, 0.30 mmol) in MeOH (10 mL), followed
by a drop of water. The solution was allowed to stir at room
temperature overnight, and then water was added (20 mL) and
the mixture was extracted with EtOAc (2 ꢂ 20 mL). After drying
over anhydrous MgSO4, the combined organic extract was fil-
tered and then concentrated in vacuo to give the crude hydroxy-
ester (S)-13. A solution of crude (S)-13 in hexane (2 mL) was
stirred under an H2 atmosphere in the presence of a catalytic
amount of 5% Pd/BaSO4 for 1 h. After filtration, concentration
and purification by flash chromatography (silica gel, 25% EtOAc
in hexane), (S)-4 was obtained (27 mg, 0.10 mmol, 35% over 2
CDCl3) d 0.86 (t, J = 6.8 Hz, 3H, H3-14), 1.23–1.46 (m, 19H), 1.56–
1.64 (m, 2H), 2.28 (t, J = 7.5 Hz, 2H, H2-2), 3.52–3.60 (m, 1H,
H-8), 3.64 (s, 3H, RCO2CH3). 13C NMR (100 MHz, CDCl3) d 14.1 (C-
14), 22.6, 24.8, 25.4, 25.6, 29.1, 29.3, 29.4, 31.8, 34.0, 37.4, 37.5,
51.5 (RCO2CH3), 71.9 (C-8), 174.3 (C-1). GC/MS EI m/z (%) 173 (5),
141 (24), 101 (19), 95 (18), 87 (36), 74 (11), 69 (18), 67 (10), 59
(19), 57 (24), 56 (9), 55 (81), 45 (12), 44 (13), 43 (97), 41 (100).
Anal. Calcd for C15H30O3: C, 69.72; H, 11.70. Found: C, 70.01; H,
11.88.
4.2.12. (S)-Methyl 8-hydroxytetradecanoate (S)-5
Following a procedure analogous to that for the synthesis of (R)-
5, the enantiomeric (S)-5 (30 mg, 0.12 mmol, 62%) was synthesised
from (S)-7 (48 mg, 0.19 mmol) and was obtained as a white solid
steps) as
¼ þ0:9 (c 2.20, CHCl3). For enantioenriched (S)-4 (74% ee)
synthesised previously,5
a
white solid (mp 28–30 °C, lit.5 29.5–30.5 °C).
½ ꢃ
a 2D5
½
a 2D5
ꢃ
¼ þ0:8 (c 1.20, CHCl3). This com-
(mp 29–30 °C). ½a D25
¼ þ1:8 (c 0.80, CHCl3). This compound was
ꢃ
pound was spectroscopically identical to the enantioenriched
spectroscopically identical to (R)-5.
(S)-4 reported previously.5
4.3. Synthesis of (R)-and (S)-methyl 7-hydroxytetradecanoates
(R)-4 and (S)-4
4.3.4. (R)-Methyl 7-hydroxytetradecanoate (R)-4
Following a procedure analogous to that described for the
synthesis of (S)-4, the enantiomeric (R)-4 (37 mg, 0.14 mmol,
4.3.1. rac-1-Methoxy-1-oxotetradec-5-yn-7-yl benzoate rac-14
Following a procedure analogous to that for the synthesis of
benzoate rac-12, benzoate rac-14 (300 mg, 0.84 mmol, 64%) was
synthesised from methyl 7-hydroxytetradec-5-ynoate5 rac-13
(330 mg, 1.31 mmol) and was obtained as a colourless oil. 1H
NMR (400 MHz, CDCl3) d 0.85 (t, J = 7.0 Hz, 3H, H3-14), 1.35–
1.22 (m, 7H), 1.51–1.44 (m, 2H), 1.89–1.77 (m, 4H), 2.27 (dt,
40% over
2 steps) was synthesised from (R)-14 (128 mg,
0.36 mmol) and was obtained as a white solid (mp 30–32 °C,
lit.5 29.5–30.5 °C). ½a 2D5
¼ ꢀ1:6 (c 0.95, CHCl3). For enantioen-
ꢃ
riched (R)-4 (68% ee) synthesised previously,5
½
a 2D5
ꢃ
¼ ꢀ1:2 (c
1.20, CHCl3). This compound was spectroscopically identical to
the enantioenriched (R)-4 reported previously.5

A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
1717
4.4. Synthesis of the threo enantiomers of methyl 7,8-
dihydroxytetradecanoate, (7S,8S)-6 and (7R,8R)-6
as a pale yellow oil. 1H NMR (500 MHz, CDCl3) d 0.86 (t, J = 7.0 Hz,
3H, H3-14), 1.15–1.38 (m, 15H), 1.55 (m, 2H), 1.95 (m, 4H, H2-6 &
H2-9), 3.62 (t, J = 6.7 Hz, 2H, H2-1), 5.36 (m, 2H, H-7 & H-8). 13C
NMR (125 MHz, CDCl3) d 14.1 (C-14), 22.6, 25.6, 28.8, 28.9, 29.55,
29.60, 31.7, 32.5, 32.6, 32.8, 63.1 (C-1), 130.1 (RHC@CHR), 130.5
(RHC@CHR). GC/MS EI m/z (%) 195 (0.1, M+ÅꢀOH), 194 (1,
M+ÅꢀH2O), 138 (1), 123 (1), 111 (1), 109 (6), 95 (14), 85 (1), 81
(25), 71 (3), 67 (44), 57 (13), 55 (56), 45 (3), 43 (39), 41 (100). Anal.
Calcd for C14H28O: C, 79.18; H, 13.29. Found: C, 78.92; H, 13.44.
4.4.1. 2-(Tetradec-7-yn-1-yloxy)tetrahydro-2H-pyran 15
n-BuLi (1.42 M in hexanes, 6.0 mL, 8.5 mmol) was added drop-
wise to a solution of 1-octyne (96%, 1.60 mL, 10.4 mmol) in anhy-
drous THF (12 mL) stirred at ꢀ40 °C under a N2 atmosphere. The
solution was stirred at ꢀ40 °C for 2.5 h, then HMPA (2.0 mL) was
added, followed 15 min later by dropwise addition of 2-(6-bro-
mohexyloxy)-tetrahydro-2H-pyran16 17 (2.45 g, 9.2 mmol). The
reaction mixture was allowed to warm to room temperature and
was stirred for 24 h. Saturated aqueous NH4Cl solution (20 mL)
was added to quench the reaction and the mixture was extracted
with petroleum spirit 40–60 (6 ꢂ 25 mL). The combined organic
extract was washed with aqueous LiCl solution (4 M, 6 ꢂ 25 mL)
and brine (4 ꢂ 25 mL), and then was dried over anhydrous MgSO4
and filtered. The solvent was removed by rotary evaporation and
the crude product was purified by flash column chromatography
(silica gel, 0.5–2% Et2O in petroleum spirit 40–60) to afford the al-
kyne 15 (2.04 g, 6.9 mmol, 81%) as a colourless oil. 1H NMR
(400 MHz, CDCl3) d 0.87 (t, J = 7.0 Hz, 3H, H3-14), 1.18–1.88 (m,
22H), 2.12 (m, 4H, H2-6 & H2-9), 3.37 (td, J = 9.6, 6.6 Hz, 1H, H-1),
3.48 (m, 1H, H-60), 3.71 (td, J = 9.6, 6.9 Hz, 1H, H-1), 3.85 (m, 1H,
H-60), 4.55 (m, 1H, H-20). 13C NMR (100 MHz, CDCl3) d 14.0 (C-
14), 18.7, 18.8, 19.7, 22.6, 25.5, 25.8, 28.5, 28.7, 29.11, 29.13,
29.7, 30.8, 31.4, 62.3 (C-60), 67.6 (C-1), 80.1 (C„C), 80.3 (C„C),
98.8 (C-20). GC/MS EI m/z (%) 294 (0.04, M+Å), 223 (1), 221 (1),
209 (1), 195 (1), 137 (1), 123 (1), 121 (2), 109 (4), 101 (7), 95
(10), 85 (71), 81 (19), 71 (2), 67 (41), 57 (14), 55 (55), 43 (47), 41
(100). Anal. Calcd for C19H34O2: C, 77.50; H, 11.64. Found: C,
77.34; H, 11.91. HRMS ESI calcd for C19H34NaO2 ([M+Na]+Å):
317.2457. Observed: 317.2437.
4.4.4. (E)-Tetradec-7-enoic acid (E)-20
To a solution of alcohol (E)-19 (220 mg, 1.04 mmol) in acetone
(25 mL) stirred at 0 °C was added Jones’ reagent (8 N) dropwise un-
til the reaction mixture remained orange in colour. The reaction
mixture was allowed to warm to room temperature with stirring
over 20 min, then was quenched by the addition of H2O (50 mL).
The mixture was extracted with Et2O (5 ꢂ 25 mL) and the com-
bined organic extract was washed with brine (3 ꢂ 25 mL) and then
was extracted with aqueous NaOH solution (5%, 5 ꢂ 25 mL). The
combined basic aqueous extract was cooled to 0 °C and concen-
trated aqueous HCl (32%, 25 mL) was added dropwise until the
solution was strongly acidic. The acidic aqueous solution was ex-
tracted with Et2O (5 ꢂ 25 mL), and the combined organic extract
was washed with brine (3 ꢂ 25 mL), dried over anhydrous MgSO4
and filtered. The solvent was removed in vacuo to afford the acid
(E)-20 (195 mg, 0.86 mmol, 83%) as a pale yellow oil. 1H NMR
(400 MHz, CDCl3) d 0.86 (t, J = 6.9 Hz, 3H, H3-14), 1.17–1.40 (m,
12H), 1.62 (m, 2H), 1.95 (m, 4H, H2-6 & H2-9), 2.33 (t, J = 7.5 Hz,
2H, H2-2), 5.36 (m, 2H, H-7 & H-8). 13C NMR (100 MHz, CDCl3) d
14.1 (C-14), 22.6, 24.5, 28.5, 28.8, 29.2, 29.6, 31.7, 32.3, 32.6,
33.8, 129.9 (RHC@CHR), 130.8 (RHC@CHR), 179.2 (C-1). GC/MS EI
m/z (%) 226 (0.2, M+Å), 164 (1), 151 (1), 137 (1), 125 (1), 123 (2),
115 (1), 111 (2), 110 (3), 101 (2), 95 (6), 91 (1), 87 (1), 85 (2), 83
(9), 79 (3), 73 (7), 71 (4), 69 (19), 67 (17), 60 (9), 59 (1), 57 (10),
55 (64), 45 (17), 43 (52), 41 (100). HRMS ESI calcd for C14H26NaO2
([M+Na]+Å): 249.1830. Observed: 249.1825.
4.4.2. (E)-2-(Tetradec-7-en-1-yloxy)tetrahydro-2H-pyran (E)-18
Lithium metal (150 mg, 21.6 mmol) was added to liquid NH3
(50 mL) stirred at ꢀ78 °C until the solution remained blue in col-
our. t-BuOH (3 mL) was added, followed by dropwise addition of
a solution of alkyne 15 (595 mg, 2.02 mmol) in anhydrous THF
(5 mL). The reaction mixture was stirred at ꢀ78 °C for 4 h, then
was allowed to slowly warm to room temperature while stirring
overnight, during which time the NH3 evaporated. Saturated aque-
ous NH4Cl solution (50 mL) was added to quench the reaction, and
the mixture was extracted with Et2O (6 ꢂ 30 mL). The combined
organic extract was washed with brine (2 ꢂ 30 mL), dried over
anhydrous MgSO4, filtered and concentrated in vacuo. The crude
product was purified by flash column chromatography (silica gel,
0.5% Et2O in petroleum spirit 40–60) to afford (E)-18 (495 mg,
1.67 mmol, 83%) as a pale yellow oil. 1H NMR (400 MHz, CDCl3) d
0.86 (t, J = 6.9 Hz, 3H, H3-14), 1.17–1.40 (m, 14H), 1.43–1.63 (m,
6H), 1.69 (m, 1H), 1.80 (m, 1H), 1.95 (m, 4H, H2-6 & H2-9), 3.36
(td, J = 9.6, 6.7 Hz, 1H, H-1), 3.48 (m, 1H, H-60), 3.71 (td, J = 9.6,
6.9 Hz, 1H, H-1), 3.85 (m, 1H, H-60), 4.55 (m, 1H, H-20), 5.36 (m,
2H, H-7 & H-8). 13C NMR (100 MHz, CDCl3) d 14.1 (C-14), 19.7,
22.6, 25.5, 26.1, 28.8, 29.0, 29.57, 29.61, 29.7, 30.8, 31.7, 32.5,
32.6, 62.3 (C-60), 67.7 (C-1), 98.8 (C-20), 130.2 (RHC@CHR), 130.5
(RHC@CHR). GC/MS EI m/z (%) 296 (0.1, M+Å), 223 (1), 205 (1),
194 (1), 138 (1), 124 (1), 111 (1), 109 (4), 101 (2), 96 (9), 85
(100), 82 (13), 71 (2), 69 (17), 67 (23), 57 (10), 55 (28), 43 (14),
41 (27). Anal. Calcd for C19H36O2: C, 76.97; H, 12.24. Found: C,
76.96; H, 12.08. HRMS ESI calcd for C19H36NaO2 ([M+Na]+Å):
319.2613. Observed: 319.2597.
4.4.5. (E)-Methyl tetradec-7-enoate (E)-16
Ethereal CH2N2 was added to a solution of acid (E)-20 (190 mg,
0.84 mmol) in MeOH (20 mL) stirred at 0 °C until the solution re-
mained yellow in colour. The reaction mixture was stirred at 0 °C
for 30 min, then was allowed to warm to room temperature and
was stirred for a further 30 min. Excess CH2N2 was evaporated un-
der a stream of N2 and the solvent was removed in vacuo to afford
the methyl ester (E)-16 (200 mg, 0.83 mmol, 99%) as a pale yellow
oil. 1H NMR (400 MHz, CDCl3) d 0.86 (t, J = 6.9 Hz, 3H, H3-14), 1.17–
1.40 (m, 12H), 1.60 (m, 2H), 1.95 (m, 4H, H2-6 & H2-9), 2.28 (t,
J = 7.6 Hz, 2H, H2-2), 3.64 (s, 3H, RCO2CH3) 5.36 (m, 2H, H-7 & H-
8). 13C NMR (100 MHz, CDCl3) d 14.1 (C-14), 22.6, 24.8, 28.6,
28.8, 29.2, 29.6, 31.7, 32.3, 32.6, 34.1, 51.4 (RCO2CH3), 129.9
(RHC@CHR), 130.7 (RHC@CHR), 174.3 (C-1). GC/MS EI m/z (%)
240 (0.6, M+Å), 209 (2), 208 (3), 190 (0.4), 179 (1), 166 (3), 151
(1), 141 (1), 137 (2), 128 (1), 125 (1), 123 (4), 115 (1), 111 (3),
110 (5), 101 (2), 96 (12), 91 (2), 87 (14), 85 (3), 84 (15), 81 (11),
74 (27), 73 (4), 71 (3), 67 (22), 59 (19), 57 (8), 55 (68), 43 (54),
41 (100). Anal. Calcd for C15H28O2: C, 74.95; H, 11.74. Found: C,
74.99; H, 11.80. HRMS ESI calcd for C15H28NaO2 ([M+Na]+Å):
263.1987. Observed: 263.1982.
4.4.6. (7S,8S)-Methyl 7,8-dihydroxytetradecanoate (7S,8S)-6
To a solution of t-BuOH and H2O (1:1, 2 mL) stirred at 0 °C was
added AD-mix-a (Aldrich, 337 mg) and methanesulfonamide (98%,
4.4.3. (E)-Tetradec-7-en-1-ol (E)-19
25 mg, 0.25 mmol). The mixture was stirred for 15 min, then a
solution of (E)-16 (54 mg, 0.23 mmol) in t-BuOH (2 mL) was added.
H2O (2 mL) was added and the reaction mixture was stirred at 4 °C
for 67 h. The reaction mixture was then re-cooled to 0 °C and solid
Following a procedure analogous to that described for the syn-
thesis of rac-10 from rac-9, THP-ether (E)-18 (495 mg, 1.67 mmol)
was deprotected to afford alcohol (E)-19 (336 mg, 1.58 mmol, 95%)

1718
A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
Na2SO3 (44 mg, 0.35 mmol) was added. The mixture was allowed
to warm to room temperature with stirring over 30 min and was
then extracted with EtOAc (5 ꢂ 10 mL). The combined organic ex-
tract was washed with brine (10 mL), dried over anhydrous MgSO4,
filtered and concentrated in vacuo. The crude product was purified
by flash column chromatography (silica gel, 50% EtOAc in petro-
leum spirit 40–60) to afford (7S,8S)-6 (50 mg, 0.18 mmol, 81%) as
a white solid (mp 35–36 °C, lit.5 mp 35–36 °C). >99% ee (Chiralpak
4.5.2. (Z)-Tetradec-7-en-1-ol (Z)-19
Following a procedure analogous to that described for the syn-
thesis of rac-10 from rac-9, THP-ether (Z)-18 (448 mg, 1.51 mmol)
was deprotected to afford alcohol (Z)-19 (301 mg, 1.42 mmol, 94%,
ꢁ10% (E)-isomer) as a pale yellow oil. 1H NMR (400 MHz, CDCl3) d
0.86 (t, J = 6.8 Hz, 3H, H3-14), 1.17–1.40 (m, 15H), 1.54 (m, 2H),
2.00 (m, 4H, H2-6 & H2-9), 3.61 (t, J = 6.6 Hz, 2H, H2-1), 5.32 (m,
2H, H-7 & H-8). 13C NMR (100 MHz, CDCl3) d 14.1 (C-14), 22.6,
25.6, 27.1, 27.2, 28.96, 29.05, 29.69, 29.71, 31.8, 32.8, 63.0 (C-1),
129.7 (RHC@CHR), 130.0 (RHC@CHR). GC/MS EI m/z (%) 195 (0.1,
M+ÅꢀOH), 194 (1, M+ÅꢀH2O), 138 (1), 123 (1), 111 (1), 109 (5), 95
(13), 85 (1), 81 (25), 71 (3), 67 (45), 57 (13), 55 (57), 45 (3), 43
(38), 41 (100). Anal. Calcd for C14H28O: C, 79.18; H, 13.29. Found:
C, 79.18; H, 13.48.
AD-H column, 2% isopropanol in hexane, flow rate 0.5 mL minꢀ1
,
UV detector 215 nm, retention time (7S,8S)-6 16.9 min. ½a D25
¼
ꢃ
ꢀ20:3 (c 0.57, MeOH). 1H NMR (400 MHz, CDCl3) d 0.87 (t,
J = 6.8 Hz, 3H, H3-14), 1.20–1.54 (m, 16H), 1.63 (m, 2H), 1.91 (d,
J = 4.2 Hz, 1H, ROH), 1.99 (d, J = 4.2 Hz, 1H, ROH), 2.30 (t,
J = 7.5 Hz, 2H, H2-2), 3.38 (m, 2H, H-7 & H-8), 3.65 (s, 3H, RCO2CH3).
13C NMR (100 MHz, CDCl3) d 14.1 (C-14), 22.6, 24.8, 25.3, 25.6,
29.1, 29.3, 31.8, 33.4, 33.6, 34.0, 51.5 (RCO2CH3), 74.4, 74.5, 174.2
(C-1). GC/MS EI m/z (%) 159 (10), 142 (5), 129 (1), 127 (25), 115
(2), 110 (17), 101 (2), 97 (6), 87 (25), 85 (3), 81 (29), 74 (20), 73
(2), 71 (4), 69 (17), 59 (20), 57 (33), 55 (92), 43 (97), 41 (100). Anal.
Calcd for C15H30O4: C, 65.66; H, 11.02. Found: C, 65.89; H, 10.87.
HRMS ESI calcd for C15H30NaO4 ([M+Na]+Å): 297.2042. Observed:
297.2029.
4.5.3. (Z)-Tetradec-7-enoic acid (Z)-20
Following a procedure analogous to that described for the
Jones’ oxidation of alcohol (E)-19 to afford acid (E)-20, alcohol
(Z)-19 (251 mg, 1.18 mmol) was oxidised to afford acid (Z)-20
(246 mg, 1.09 mmol, 92%, ꢁ10% (E)-isomer) as a pale yellow oil.
1H NMR (400 MHz, CDCl3) d 0.86 (t, J = 6.9 Hz, 3H, H3-14), 1.17–
1.40 (m, 12H), 1.62 (m, 2H), 1.98 (m, 4H, H2-6 & H2-9), 2.33 (t,
J = 7.5 Hz, 2H, H2-2), 5.33 (m, 2H, H-7
&
H-8). 13C NMR
(100 MHz, CDCl3) d 14.1 (C-14), 22.6, 24.6, 27.0, 27.2, 28.7, 29.0,
29.3, 29.7, 31.8, 34.0, 129.4 (RHC@CHR), 130.3 (RHC@CHR),
179.8 (C-1). GC/MS EI m/z (%) 226 (0.2, M+Å), 208 (1), 164 (1),
137 (1), 125 (1), 123 (2), 115 (1), 111 (2), 110 (3), 101 (2), 96
(6), 91 (1), 87 (2), 85 (2), 83 (9), 79 (4), 73 (7), 71 (4), 69 (20),
67 (16), 60 (8), 59 (3), 57 (10), 55 (65), 45 (14), 43 (51), 41
(100). Anal. Calcd for C14H26O2: C, 74.29; H, 11.58. Found: C,
73.89; H, 11.57. HRMS ESI calcd for C14H26NaO2 ([M+Na]+Å):
249.1830. Observed: 249.1817.
4.4.7. (7R,8R)-Methyl 7,8-dihydroxytetradecanoate (7R,8R)-6
Following a procedure analogous to that described for the syn-
thesis of (7S,8S)-6, (E)-16 (54 mg, 0.23 mmol) was dihydroxylated
by the action of AD-mix-b (Aldrich, 339 mg) over 115 h to afford
(7R,8R)-6 (46 mg, 0.17 mmol, 75%) as a white solid (mp 35–36 °C,
lit.5 mp 35–36 °C). >99% ee (Chiralpak AD-H column, 2% isopropa-
nol in hexane, flow rate 0.5 mL minꢀ1, UV detector 215 nm, reten-
tion time (7R,8R)-6 16.0 min. ½a D25
¼ þ21:0 (c 0.51, MeOH). This
ꢃ
compound was spectroscopically identical to (7S,8S)-6. Anal. Calcd
for C15H30O4: C, 65.66; H, 11.02. Found: C, 65.69; H, 10.99. HRMS
ESI calcd for
297.2033.
4.5.4. (Z)-Methyl tetradec-7-enoate (Z)-16
C
15H30NaO4 ([M+Na]+Å): 297.2042. Observed:
Following a procedure analogous to that described for the syn-
thesis of ester (E)-16 from acid (E)-20, acid (Z)-20 (195 mg,
0.86 mmol) was esterified using ethereal diazomethane to afford
the methyl ester (Z)-16 (198 mg, 0.82 mmol, 96%, ꢁ10% (E)-iso-
mer) as a colourless oil. 1H NMR (400 MHz, CDCl3) d 0.86 (t,
J = 6.9 Hz, 3H, H3-14), 1.17–1.40 (m, 12H), 1.61 (m, 2H), 2.00 (m,
4H, H2-6 & H2-9), 2.28 (t, J = 7.6 Hz, 2H, H2-2), 3.65 (s, 3H,
RCO2CH3) 5.32 (m, 2H, H-7 & H-8). 13C NMR (100 MHz, CDCl3) d
14.1 (C-14), 22.6, 24.9, 27.0, 27.2, 28.8, 29.0, 29.4, 29.7, 31.8,
34.1, 51.4 (RCO2CH3), 129.4 (RHC@CHR), 130.2 (RHC@CHR), 174.3
(C-1). GC/MS EI m/z (%) 240 (0.2, M+Å), 209 (1, M+ÅꢀOCH3), 208 (2,
M+ÅꢀMeOH), 166 (2), 151 (1), 141 (1), 137 (1), 128 (1), 125 (1),
123 (2), 115 (1), 111 (2), 110 (3), 101 (1), 96 (9), 86 (10), 85 (3),
81 (9), 74 (23), 73 (3), 71 (2), 67 (18), 59 (18), 57 (7), 55 (61), 43
(54), 41 (100). Anal. Calcd for C15H28O2: C, 74.95; H, 11.74. Found:
C, 74.67; H, 11.99. HRMS ESI calcd for C15H28NaO2 ([M+Na]+Å):
263.1987. Observed: 263.1982.
4.5. Synthesis of the erythro enantiomers of methyl 7,8-
dihydroxytetradecanoate, (7S,8R)-6 and (7R,8S)-6
4.5.1. (Z)-2-(Tetradec-7-en-1-yloxy)tetrahydro-2H-pyran (Z)-18
A flask containing a solution of alkyne 15 (502 mg, 1.70 mmol)
in EtOAc (20 mL) was evacuated and purged twice with N2 gas,
then twice with H2 gas. Lindlar’s catalyst (5% Pd on CaCO3 poisoned
with lead, 42 mg) was added and the mixture was stirred under a
H2 atmosphere for 30 min at room temperature. The reaction mix-
ture was filtered through a pad of Celite™, which was thoroughly
washed with additional EtOAc. The filtrate was concentrated in va-
cuo and the residue was purified by flash column chromatography
(silica gel, 1–2% EtOAc in petroleum spirit 40–60) to afford (Z)-18
(504 mg, 1.70 mmol, quantitative, ꢁ10% (E)-isomer) as a colourless
oil. 1H NMR (400 MHz, CDCl3) d 0.86 (t, J = 6.9 Hz, 3H, H3-14), 1.17–
1.43 (m, 14H), 1.43–1.63 (m, 6H), 1.69 (m, 1H), 1.80 (m, 1H), 1.99
(m, 4H, H2-6 & H2-9), 3.36 (td, J = 9.6, 6.7 Hz, 1H, H-1), 3.48 (m, 1H,
H-60), 3.71 (td, J = 9.6, 6.9 Hz, 1H, H-1), 3.85 (m, 1H, H-60), 4.55 (m,
1H, H-20), 5.32 (m, 2H, H-7 & H-8). 13C NMR (100 MHz, CDCl3) d
14.0 (C-14), 19.7, 22.6, 25.5, 26.1, 27.1, 27.2, 29.0, 29.1, 29.69,
29.72 (2C), 30.8, 31.8, 62.3 (C-60), 67.6 (C-1), 98.8 (C-20), 129.7
(RHC=CHR), 130.0 (RHC@CHR). GC/MS EI m/z (%) 296 (0.02, M+Å),
281 (0.03, M+ÅꢀCH3), 138 (1), 123 (1), 111 (1), 109 (3), 101 (3),
95 (8), 85 (86), 81 (16), 71 (3), 69 (19), 67 (34), 57 (18), 55 (68),
43 (47), 41 (100). Anal. Calcd for C19H36O2: C, 76.97; H, 12.24.
4.5.5. erythro-Methyl 7,8-dihydroxytetradecanoate erythro-6
Following a procedure analogous to that described for the syn-
thesis of (7S,8S)-6 from (E)-16, (Z)-16 (47 mg, 0.20 mmol) was
dihydroxylated by the action of AD-mix-a (Aldrich, 300 mg) over
210 h to afford a mixture of (7R,8S)- and (7S,8R)-methyl 7,8-
dihydroxytetradecanoate erythro-6 (52 mg, 0.19 mmol, 97%) as a
white solid (mp 89–90 °C). ½a D25
ꢃ
¼ þ0:4 (c 0.42, MeOH). 1H NMR
(500 MHz, CDCl3) d 0.87 (t, J = 6.9 Hz, 3H, H3-14), 1.20–1.54 (m,
16H), 1.63 (m, 2H), 1.76 (br s, 1H, ROH), 1.80 (br s, 1H, ROH),
2.30 (t, J = 7.5 Hz, 2H, H2-2), 3.57 (m, 2H, H-7 & H-8), 3.65 (s, 3H,
RCO2CH3). 13C NMR (125 MHz, CDCl3) d 14.1 (C-14), 22.6, 24.8,
25.6, 26.0, 29.1, 29.3, 30.9, 31.3, 31.8, 34.0, 51.5 (RCO2CH3), 74.5,
74.7, 174.2 (C-1). GC/MS EI m/z (%) 207 (0.3), 189 (1), 159 (14),
Found: C, 76.84; H, 12.27. HRMS ESI calcd for
C19H36NaO2
([M+Na]+Å): 319.2613. Observed: 319.2595.

A. A. Singh et al. / Tetrahedron: Asymmetry 22 (2011) 1709–1719
1719
145 (1), 142 (8), 129 (1), 127 (37), 115 (1), 110 (24), 101 (2), 97 (4),
J = 8.0 Hz, 2H). HRMS ESI calcd for
C
33H46NaO8 ([M+Na]+Å):
87 (29), 85 (2), 81 (39), 74 (21), 73 (2), 71 (4), 69 (16), 59 (17), 57
(39), 55 (99), 43 (100), 41 (87). Anal. Calcd for C15H30O4: C, 65.66;
H, 11.02. Found: C, 65.51; H, 11.17. HRMS ESI calcd for C15H30NaO4
([M+Na]+Å): 297.2042. Observed: 297.2030.
593.3090. Observed: 593.3103.
4.5.7. (7R,8S)-Methyl 7,8-dihydroxytetradecanoate (7R,8S)-6
Powdered solid NaOH (80 mg, 2.0 mmol) was added to a solu-
tion of (7R,8S)-21 (29 mg, 51 lmol) in MeOH (10 mL), followed
4.5.6. (7R,8S)- and (7S,8R)-Methyl 7,8-bis((S)-2-methoxy-2-
phenylacetoxy)tetradecanoates (7R,8S)-21 and (7S,8R)-21
To a solution of dihydroxyester mixture erythro-6 (45 mg,
0.16 mmol) in anhydrous CH2Cl2 (3 mL) under a N2 atmosphere
was added DCC (135 mg, 0.65 mmol), DMAP (80 mg, 0.65 mmol)
and (S)-methoxyphenylacetic acid (110 mg, 0.66 mmol) and the
resulting solution was stirred at room temperature overnight. After
filtration of the precipitate and removal of the CH2Cl2 in vacuo, the
crude material (45:55 mixture of two diastereomers, >99% ee, 10%
de) was subjected to preparative separation by enantioselective
HPLC (Chiralpak AD-H column, 10% isopropanol in hexane, flow
rate 10 mL minꢀ1, UV detector 254 nm, retention times: (7R,8S)-
21 22.8 min, (7S,8R)-21 28.6 min). Both diastereomers were ob-
tained optically pure (>99% de and ee; 74% combined yield) and
their absolute configurations were determined by NMR
spectroscopy.
by a drop of water. The solution was allowed to stir at room tem-
perature overnight and then dilute aqueous HCl solution (1%,
15 mL) was added. The mixture was extracted with CH2Cl2
(3 ꢂ 20 mL) and the combined organic extract was washed with
brine (20 mL) and water (20 mL). After drying over anhydrous
MgSO4, the organic extract was filtered and then concentrated in
vacuo. The crude product was purified by flash chromatography
(25% EtOAc in hexane) to afford (7R,8S)-6 (9 mg, 33 lmol, 65%)
as a white solid (mp 96 °C). ½a D25
¼ þ1:7 (c 0.40, CHCl3). This com-
ꢃ
pound was spectroscopically identical to the essentially racemic
mixture erythro-6.
4.5.8. (7S,8R)-Methyl 7,8-dihydroxytetradecanoate (7S,8R)-6
Following an analogous procedure to that described for the syn-
thesis of (7R,8S)-6 from (7R,8S)-21, the desired compound (7S,8R)-
6 (9 mg, 33
lmol, 58%) was synthesised from (7S,8R)-21 (32 mg,
(7R,8S)-21: 30 mg, 53
l
mol, 32%. Colourless oil. ½a D25
ꢃ
¼ þ72:2 (c
56 mol) and was obtained as a
l
white solid (mp 94 °C).
0.34, CHCl3). 1H NMR (400 MHz, CDCl3) d 0.51–0.73 (m, 2H), 0.79–
0.96 (m, 2H), 0.89 (t, J = 6.8 Hz, 3H, H3-14), 1.02–1.34 (m, 12H),
1.43–1.54 (m, 2H), 2.08 (t, J = 7.6 Hz, 2H, H2-2), 3.42 (s, 3H), 3.43
(s, 3H), 3.68 (s, 3H), 4.46 (s, 1H), 4.75 (dt, J = 10.0, 3.5 Hz, 1H, H-
7), 4.77 (s, 1H), 5.14 (dt, J = 8.6, 4.2 Hz, 1H, H-8), 7.25–7.33 (m,
5H), 7.36–7.41 (m, 3H), 7.46–7.49 (m, 2H). 13C NMR (100 MHz,
CDCl3) d 14.0, 22.5, 24.0, 24.4, 25.3, 27.5, 28.3, 28.9, 30.2, 31.5,
33.7, 51.4 (RCO2CH3), 57.3, 57.5, 74.4, 74.7, 82.1, 82.5, 127.1 (2C),
127.3 (2C), 128.4 (2C), 128.5 (2C), 128.6, 128.7, 136.4, 136.5,
170.1, 170.3, 174.0 (C-1). 1H NMR (400 MHz, C6D6) d 0.64–0.99
(m, 3H), 0.86 (t, J = 7.2 Hz, 3H, H3-14), 1.05–1.47 (m, 15H), 1.96
(t, J = 7.5 Hz, 2H, H2-2), 3.24 (s, 3H), 3.36 (s, 3H), 3.38 (s, 3H),
4.59 (s, 1H), 4.71 (s, 1H), 4.94 (dt, J = 10.3, 3.2 Hz, 1H, H-7), 5.39
(dt, J = 9.8, 3.5 Hz, 1H, H-8), 7.06–7.18 (m, 6H), 7.46 (br d,
J = 8.0 Hz, 2H), 7.57 (br d, J = 8.0 Hz, 2H). HRMS ESI calcd for
½
a 2D5
ꢃ
¼ ꢀ2:3 (c 0.24, CHCl3). This compound was spectroscopically
identical to the essentially racemic mixture erythro-6.
Acknowledgments
A.A.S. is grateful for Australian Postgraduate Award scholarship
support and S.N.A.Z. is grateful for a University of Queensland
Summer Research Scholarship.
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