Synthesis and preliminary antibacterial evaluation of simplified thiomarinol analogs

Article abstract of DOI:10.1016/j.bmc.2008.01.001

A series of simplified thiomarinol derivatives was prepared by way of catalytic enantioselective inverse electron demand hetero [4 + 2] cycloaddition/allylboration tandem reaction. As a preliminary evaluation, these analogs were tested for antimicrobial a

Full text of DOI:10.1016/j.bmc.2008.01.001

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 17 (2009) 1006–1017
Synthesis and preliminary antibacterial evaluation of simplified
thiomarinol analogs
Olivier Marion, Xuri Gao, Sandra Marcus and Dennis G. Hall*
Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2G2
Received 24 November 2007; accepted 4 January 2008
Available online 9 January 2008
Dedicated to Professor Jon Ellman on receipt of the 2006 Tetrahedron Young Investigator Award in Bioorganic and Medicinal Chemistry
Abstract—A series of simplified thiomarinol derivatives was prepared by way of catalytic enantioselective inverse electron demand
hetero [4 + 2] cycloaddition/allylboration tandem reaction. As a preliminary evaluation, these analogs were tested for antimicrobial
activity using a standard disk diffusion assay. Whereas amide analogs were less active, the simple ester analogs 3 and 4 were dem-
onstrated to be more active than thiomarinol H.
ꢀ 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Mupirocin (pseudomonic acid A, Fig. 1) is one of the
worlds’ leading topical antibiotics commercialized under
the name Bactrobanꢁ by GlaxoSmithKline.1 It is pro-
duced by Pseudomonas fluorescens, a soil isolate re-
ported to possess antibacterial activity as early as
1887.2 While the mixture of pseudomonic acids was
found to be the active component in the 1960s,3 the ma-
jor constituent was characterized later and named
pseudomonic acid A (mupirocin).4 Mupirocin is active
against Gram-positive aerobic bacteria and a few
Gram-negative strains. It is prescribed for treating skin
infections such as impetigo, candidiasis, burn wounds,
and cuts.
Mupirocin inhibits the bacterial isoleucyl tRNA synthe-
tase enzyme responsible for loading the aminoacid isoleu-
cine (Ile) onto its cognate tRNA required for ribosomal
protein synthesis (Fig. 2).5 Aminoacyl tRNA synthetases
belong to a superfamily of nucleotidyl transferase en-
zymes related to other ATP-binding proteins such as
dehydrogenases and photolyase. There is at least one dis-
crete synthetase per specific aminoacid. These enzymes
are divided into two related classes, I or II, depending
on whether they acylate the 20 or 30 end of the tRNA
Figure 1. Structures of mupirocin (pseudomonic acid A) and selected
members of the thiomarinol family.
Keywords: Thiomarinol analogs; Antibacterial; Mupirocin; Cycload-
dition/allylboration tandem reaction.
(Fig. 2).6 Some synthetases, such as tRNAIle synthetase
(a class I synthetase), even possess an editing site for cor-
*
Corresponding author. Tel.: +1 780 492 3141; fax: +1 780 492
8231; e-mail: dennis.hall@ualberta.ca
0968-0896/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.01.001

O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
1007
analogs embodying the monate core and a sulfonamido-
isoleucyl side chain.10 The X-ray crystal structure of mup-
irocin bound to the complex between tRNAIle synthetase
and its cognate tRNA was solved in 1999.11 The structure
confirmed that the right-hand side chain of mupirocin
does not occupy the site that would normally stabilize
the phosphatidyl isoleucine. The structure also confirmed
that mupirocin acts mainly as an ATP mimic and occupies
the site normally occupied by the ribose ring. A map of the
main molecular interactions in the mupirocin–tRNAIle
complex is shown in Figure 3. Critical to the inhibitor
complex is a p–p* interaction between Phe587 and the
acrylate moiety, which is also held in place with a back-
bone hydrogen bond between Val588 and the carbonyl
oxygen.
Due to their structure and their biological activity, the
pseudomonic acids have attracted considerable atten-
tion from synthetic and medicinal chemists.12 Unfortu-
nately, mupirocin displays poor oral absorptivity and
low metabolic stability. In the bloodstream, its ester
linkage is rapidly hydrolyzed to an inactive product,
monic acid (Fig. 1).13 Consequently, there has been sig-
nificant interest in the development of improved analogs
that could also be suitable as oral antibiotics. Thiomar-
inol A14 and thiomarinol H15 (Fig. 1) are rare marine
natural products recently isolated from the bacterium
Alteromonas rava sp. nov. SANK 73390. These closely
related families of naturally occurring antibiotics display
minor structural differences. The structures of thiomari-
nols A and H differ from mupirocin by the presence of a
C4-hydroxyl, a shorter C1-alkoxy chain, and the
replacement of the C10–C11 epoxide with an E alkene
unit. Based on the X-ray crystal structure of the mupiro-
cin–tRNAIle synthetase complex, we speculated that the
additional 4-hydroxyl group in thiomarinols might be
able to form hydrogen bonds with His64 and Asp557
in the bacterial enzyme (Fig. 4). The role of the addi-
tional 4-hydroxyl group is intriguing and deserves fur-
ther investigation because thiomarinol analogs might
demonstrate improved antimicrobial activity. Thiomari-
nols A and H are distinguishable by their respective
holotin and anhydroornithine C1 amide end-groups.
These natural substances were found to be equally po-
Figure 2. Biomechanism of action for tRNAIle synthetase, a class I
aminoacyl tRNA synthetase.
recting misloaded aminoacids. The synthetase site of
these enzymes holds substrates in place without involving
functional groups of the enzyme in a chemical sense (i.e.,
without the involvement of any covalent bonds or proton
exchange). Instead, it stabilizes with very conserved resi-
dues (the so-called HIGH box) the transition state for
cleavage of the a-phosphate upon nucleophilic attack by
the aminoacid carboxylate.7
These enzymes are characterized by the presence of a
Rossman-like dinucleotide-binding fold consisting in a/
b tertiary structure, which is very common amongst aden-
ylyl and cytidylyl triphosphate binding enzymes. Mupiro-
cin is approximately 10,000 times more potent on the
bacterial enzyme than the human homolog, which ensures
its selectivity as a pharmaceutical drug.8 The binding of
mupirocin to the enzyme–tRNA complex is competitive
with isoleucine and ATP, and also with Ile-AMP deriva-
tives. Surprisingly, tryptophan fluorescence studies re-
vealed that the epoxide-containing side chain does not
occupy the site of the other enzyme substrate, isoleucine,
but rather an adjacent site slightly off from the residues
normally involved in phosphate anion stabilization.9 This
information was elegantly employed in a recent report
describing the preparation of subnanomolar chimeric
Figure 3. Map of main molecular interactions in the mupirocin–
tRNAIle complex.11

1008
O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
Figure 5. Qualitative pharmacophore model for mupirocin.
they did not display good in vitro activity (i.e., high
MIC values) probably because of their lipophilic charac-
ter. Monic ester analogs with additional substituents in
the 2-position, like the 2-fluoro and 2-methyl deriva-
tives, retain most of the antimicrobial activity provided
that the olefin geometry is not inverted.18 To improve
the oral bioavailability of the compounds, the left-hand
alkoxy group on the hydrolizable ester was replaced
with various carboxyl group surrogates such as hetero-
cycles like diazoles and triazoles.19 Unfortunately, most
of these derivatives are inactive. Allylic ethers and ke-
tones were also evaluated.20 Whereas the ethers demon-
strated good IC50 values but low in vitro activity, some
of the ketones were active in vitro. Modifications of the
right-hand side chain (C9–C14) were also examined.21
Surprisingly, even subtle changes to the terminal C12–
C14 unit are not well tolerated. Thus, both the C13-
deoxy analog and the analog with inverted stereochem-
istry showed weak activity.
Figure 4. His64 (bottom spheres) and Asp557 (top spheres) near the
C4 center of mupirocin (sticks) complexed to the bacterial tRNA
isoleucyl synthetase.11
tent to pseudomonic acid A, and thiomarinol A was
found to possess a wider spectrum of activity (against
both Gram-positive and -negative bacteria).14 For
example, the activity of thiomarinol H against Staphylo-
coccus aureus was shown to be comparable to that of tet-
racycline and streptomycin.15 These impressive
properties justify efforts to develop synthetic routes to
the thiomarinols. Our group has recently synthesized
the first member of the thiomarinol family, thiomarinol
H, using a synthetic route that could be amenable to the
design of simplified analogs.16 At the onset of this pro-
ject on the evaluation of thiomarinol analogs, several
questions arose: (1) What is the contribution of the
left-hand side chain and the heterocyclic end-group in
the thiomarinols? (2) What is the contribution of the
C4-hydroxy group of thiomarinols. (3) Is the right-hand
side chain necessary in its integral form? These questions
can be addressed with simple analogs that are easily
accessible as a result of our unique synthetic approach
to the thiomarinol skeleton. We hoped that the informa-
tion gained could lead to further improvements through
the design of second-generation analogs.
To address the effect of the structural differences be-
tween mupirocin and the thiomarinols on their respec-
tive antimicrobial activity, we planned the design of
simple analogs 1–6 with a simplified ester or an amide
as left-hand side chain (Fig. 6). It was hoped that amide
analogs, such as 5 and 6, could preserve a high antibac-
terial activity without the hydrolytic susceptibility of
2. Results
2.1. Design of simplified analogs
It is believed that mupirocin and the thiomarinols share
the same target, bacterial isoleucine tRNA synthetase.
Extensive medicinal chemistry studies have been per-
formed on pseudomonic acid analogs and the outcome
of these studies can be of help with the thiomarinol fam-
ily. A precise pharmacophore model of mupirocin was
developed even before the availability of X-ray crystal-
lographic information (Fig. 5). The dihydroxypyran
(monate) unit is essential for the antibacterial activity.
It was shown that the left-hand side chain and the acry-
late linker are quite variable provided that a suitable iso-
electronic replacement such as a N,O-heterocyclic unit is
used as the linker.17 While most of these analogs pos-
sessed potent IC50 values when assayed enzymatically,
Figure 6. Structures of simplified thiomarinol analogs evaluated in this
study.

O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
1009
mupirocin. Furthermore, we designed analogs 7–9 lack-
ing a right-hand (C9–C14) side chain and analog 10 with
a simplified side chain devoid of the C13 hydroxyl and
other substituents. The preliminary evaluation of these
analogs will reveal the extent to which the thiomarinol
core can be simplified toward designing more potent
analogs.
All of these analogs were prepared by way of our cata-
lytic enantioselective inverse electron demand hetero
[4 + 2] cycloaddition/allylboration tandem reaction be-
tween boronate-containing heterodiene 11, enol ethers
(12), and aldehydes (15) (Scheme 1).22 The cycloaddition
step is catalyzed by Jacobsen’s Cr(III) complex 13.23
This multicomponent reaction functions well with a
wide range of enol ethers and aldehydes, and was dem-
onstrated in the context of complex target synthesis, as
exemplified by thiomarinol H.16 Acetal reduction and
a stereoselective dihydroxylation of dihydropyrans 16
would afford the desired analogs.
Scheme 2. Preparation of acid 1 and simplified ester analogs 2–4.
2.2. Preparation of analogs
Analogs 2–4 with a simplified ester as well as the amide
analogs 5 and 6 were prepared from an advanced syn-
thetic intermediate, carboxylic acid 17 (Scheme 2), made
in our total synthesis of thiomarinol H.16 Intermediate
17 can be reached in a dozen steps following the initial
key multicomponent reaction depicted in Scheme 1.
Then, the siloxy groups of 17 were removed using tetra-
butylammonium fluoride to give intermediate 18. The
latter was subjected to an alkylative esterification with
different alkyl iodides to provide the ester analogs 2–4
after hydrolysis of the acetonide with aqueous acetic
acid. The free carboxylic acid analog 1 was made from
18 by direct treatment with aqueous acetic acid. The
respective secondary and tertiary amide analogs 5 and
6 were synthesized with a similar sequence that com-
menced with a PyBroP-promoted amidation to provide
protected intermediates 19 and 20 (Scheme 3). These
two intermediates were treated as above to remove the
siloxy groups and unblock the acetonide-protected diol,
providing analogs 5 and 6.
Scheme 3. Preparation of amide analogs 5 and 6.
Analogs 7–9 with a simplified ester and no right-hand
side chain as well as analog 10 with a simplified right-
hand chain were prepared from the [4 + 2] cycloaddition
between heterodiene 11 and enol ethers 21 and 22 to
produce adducts 23 and 24, which were reacted with
aldehydes 25–27 to generate allylboration products 28–
31 in good yields and high ee (Scheme 4). The hydroxyl
groups of intermediates 28–31 were protected as siloxy
ether prior to the silane-promoted reduction of the ace-
tal to generate intermediates 32–35. Stereo-selective
dihydroxylation of the pyran’s alkene was achieved by
reaction with osmium tetraoxide. The resulting four
intermediates were then treated with TBAF (in the pres-
ence of acetic acid in the case of the furanone analogs) as
above to provide the desired analogs 7–10.
Scheme 1. Three-component hetero [4 + 2] cycloaddition/allylboration
reaction approach to thiomarinol analogs.

1010
O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
Scheme 4. Preparation of simplified analogs 7–10. NMO = N-methyl morpholine oxide, TABF = tetra-n-butylammonium fluoride, TIPS =
triisopropylsilyl.
2.3. Evaluation of antibacterial activity
cyl tRNA synthetase because there are other factors
such as bioavailability that might be limiting (e.g., solu-
bility and the ability to cross the bacterial membrane).
Thus, to clarify the role of the 4-hydroxyl group in thio-
marinols, more studies are required.
As a preliminary evaluation, analogs 1–10 were tested
for antimicrobial activity against S. aureus using a stan-
dard disk diffusion assay.24 The diameter of zones with
complete growth inhibition induced by commonly used
antibiotics and our simplified thiomarinol analogs were
compared. The larger the diameter of the zone, the more
active the analogs. Control antibiotics were streptomy-
cin, penicillin G, and pseudomonic acid A.
Analogs lacking the right-hand side chain 7–9 as well as
the ester analog with the simplified right-hand side chain
10 did not show any antimicrobial activity in the disk
diffusion assay (i.e., no zone of inhibition). It was hoped
that analog 8 (with the trans double bound) would show
some in vitro activity on the basis of the inherent prote-
olytic stability of the lactone ring. On the other hand, it
was expected that analog 9 would be less active based on
previous studies on the olefin geometry of mupirocin
analogs.18 The fact that analog 10 did not inhibit bacte-
rial growth strongly suggests that the right-hand side
chain of the natural molecule must remain mostly intact
to keep the activity. This conclusion is in agreement with
results obtained with the C12–C14 mupirocin analogs.21
Using this simple but reliable assay, it was found that
synthetic thiomarinol H was more active than tetracy-
cline–HCl, but less active than streptomycin, penicillin
G, and pseudomonic acid A (Table 1). Among the sim-
plified analogs, not surprisingly, the acid derivative 1 did
not show any antimicrobial activity, an outcome similar
to monic acid.13 While the amide analogs 5 and 6 are
inferior to thiomarinol H in terms of activity, the simpli-
fied ester analogs, especially the ethyl and isopropyl es-
ters 3 and 4, demonstrated stronger inhibition. Although
the simplified ester analogs of thiomarinols exhibit
slightly lower antimicrobial in vitro activity than
pseudomonic acid A, it does not necessarily mean that
thiomarinols are inferior ligands for the bacterial isoleu-
The information gained in this study will help us design
more potent thiomarinol analogs. Key targets for a sec-
ond-generation of derivatives would be esters similar to
analogs 3 and 4. Analogs bearing a lactone ring on the

O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
Table 1. Disk diffusion assay against Staphylococcus aureus
1011
4. Experimental
Compound
Amount
loaded
on disk
(·10ꢀ2 lmol)
Strains
Inhibition zonea (mm)
4.1. General
ATCC#6538 ATCC#25923
Unless otherwise stated, all reactions was performed un-
der a nitrogen atmosphere using flame-dried glassware.
Toluene and CH2Cl2 were distilled from CaH2. All alde-
hydes were purified by bulb-to-bulb distillation prior to
use. Analytical thin layer chromatography were per-
formed on Merck Silica Gel 60 F254 plates and were
visualized with UV light and 1% KMnO4 (aq). Deacti-
vated silica-gel refers to the silica-gel washed with trieth-
ylamine prior to use. NMR spectra were recorded on
Varian INOVA-300, INOVA-400 or INOVA-500 MHz
instruments. The residual solvent protons (1H) or the
solvent carbon (13C) were used as internal standards.
1H NMR data are presented as follows: chemical shift
in ppm (d) downfield from tetramethylsilane (multiplic-
ity, coupling constant, integration). The following
abbreviations are used in reporting NMR data: s, sin-
glet; br s, broad singlet; d, doublet; t, triplet; q, quartet;
dq, doublet of quartets; dd, doublet of doublets; m, mul-
tiplet. High-resolution mass spectra were recorded by
the University of Alberta mass spectrometry service lab-
oratory using either electron impact (EI) or electrospray
ionization (ESI) techniques. Infrared spectra were ob-
tained on a Nicolet Magna-IR 750 with frequencies ex-
pressed in cmꢀ1. X-ray crystallography was performed
using a Bruker P4/RA/SMART 1000 CCD diffractome-
ter. Catalyst 13 was prepared according to the procedure
of Jacobsen and co-workers.23 Boronate 11 was pre-
pared according to our previously published procedure
and purified by bulb-to-bulb distillation (<1 mmHg,
94%).25 The preparation of intermediate 17 was reported
before.16 BaO (Acros) was used as supplied (90% tech-
powder). Optical rotations were measured using a 1-
mL cell with a 1-dm length on a Perkin-Elmer 241
polarimeter.
Streptomycin sulfate 0.686
Tetracycline–HCl 6.02
Penicillin G Na salt 1.9
16
28
40
32
14
29
32
26
Pseudomonic acid
A Ca salt
Thiomarinol H
1.72
1.72
1.72
1.72
1.72
1.72
3.44
3.44
1.72
1.72
1.72
1.72
16
10
1
2
3
4
5
6
7
8
9
10
No zone
16
22
No zone
13
21
22
14
21
Slight
Slight
No zone
No zone
No zone
No zone
15
No zone
No zone
No zone
No zone
a Diameter of zones with complete growth inhibition. One represen-
tative set of data is shown.
left-hand side chain and the unmodified right-hand side
chain would be of particular interest considering the
probable in vivo stability of the heterocycle. Changes
to the right-hand side chain could be inspired by the
studies of Pope and co-workers.10 Finally, the prepara-
tion of C4–deoxy thiomarinol analogs would greatly
help in clarifying the role of this particular hydroxyl
group in the biological activity of this class of
antibiotics.
3. Conclusions
Thiomarinols are rare marine natural products closely
related to mupirocin. The preparation of simplified thi-
omarinol analogs will help in the quest to generate an
orally available (with high metabolic stability) derivative
of mupirocin. In this study, the efficient enantioselective
inverse electron demand hetero [4 + 2] cycloaddition/
allylboration tandem reaction developed in our labora-
tory was used to prepare rationally designed thiomari-
nol analogs. As a preliminary evaluation of their
antimicrobial activity, these simplified analogs were
tested against two strains of S. aureus using a simple
disk diffusion assay. The evaluation of these analogs
has provided insight into the extent to which the thio-
marinols can be simplified while maintaining a potent
activity. Interestingly, the simplified ester analogs 3
and 4 were demonstrated to be more active than thio-
marinol H, showing that the left-hand side chain and
the heterocyclic end-group are not essential for the anti-
microbial activity. On the other hand, analogs 7–10 did
not show any antimicrobial activity suggesting that the
right-hand chain is necessary in its integral form. Also,
amide analogs 5 and 6 were inferior to thiomarinol H
in the disk diffusion assay. Although more studies will
be required to clarify the role of the C4-hydroxyl group
of the thiomarinols, the information gained in this study
will be very useful in the design of improved second-gen-
eration analogs.
4.2. Preparation of analogs
4.2.1. (4R)-{(2S,3R,4R,5S)-3,4-O-Isopropylidene-3,4-
dihydroxy-5-[(4R,5S)-4-methyl-5-hydroxy-hex-2-enyl]-
tetrahydro-pyran-2-yl}-3-methyl-4-hydroxy-but-2E-enoic
acid (18). To the solution of TIPS protected alcohol 17
(0.210 g, 0.301 mmol) in THF (3 mL) was added TBAF
(2.41 mL. 1.00 M solution in THF, 2.410 mmol). The
reaction mixture was stirred at ambient temperature
for 24 h and quenched with an saturated aqueous solu-
tion of NH4Cl (10 mL). The layers were separated,
and the aqueous layer was extracted with EtOAc (2·
20 mL). The combined organic layers were washed with
water (20 mL) brine (20 mL), dried over anhydrous
Na2SO4, filtered, concentrated, and purified by flash col-
umn chromatography (EtOAc/MeOH, 9:1) to afford the
23
D
title compound 18 (0.083 g, 81%) as a yellow oil. ½aꢁ
ꢀ7.8 (c 0.3, CHCl3); IR (CHCl3, cast, cmꢀ1) 3420,
1690, 1646; 1H NMR (500 MHz, CDCl3) d 6.02 (s,
1 H), 5.41–5.57 (m, 2H), 4.12–4.22 (m, 3H), 3.75 (dd,
J = 3.1, 11.5 Hz, 1H), 3.66 (dd, J = 1.6, 11.5 Hz, 1H),
3.55–3.63 (m, 1H), 3.41 (dd, J = 2.3, 8.4 Hz, 1H),
2.00–2.32 (m, 7H), 1.48 (s, 3H), 1.38 (s, 3H), 1.16 (d,
J = 6.3 Hz, 3H), 1.01 (d, J = 6.9 Hz, 3H); 13C NMR

1012
O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
(125 MHz, CDCl3) d 170.9, 159.7, 134.9, 128.9, 115.9,
108.8, 77.7, 75.6, 75.3, 71.2, 70.2, 66.5, 44.4, 36.5, 34.0,
28.3, 26.3, 20.3, 16.6, 16.0; HRMS (ESI, m/z) calcd for
C20H33O7 [M + H] 385.22208, found 385.22213.
3.52–3.58 (m, 2H), 2.03–2.23 (m, 6H), 1.82–1.88 (m,
1H), 1.28 (t, J = 7.1 Hz, 3H), 1.16 (d, J = 6.1 Hz, 3H),
0.99 (d, J = 6.9 Hz, 3H); 13C NMR (125 MHz, CDCl3)
d 166.9, 158.2, 134.5, 129.1, 115.8, 75.8, 73.8, 71.4,
70.4, 65.3, 64.6, 59.8, 44.6, 41.5, 32.4, 20.6, 16.8, 16.0,
14.3; HRMS (ESI, m/z) calcd for C19H33O7 373.22208,
found 373.22238.
4.2.2. (4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-4-
methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-3-
methyl-4-hydroxy-but-2E-enoic acid (1). A solution of 18
(32.0 mg, 0.056 mmol) in 80% aqueous AcOH (0.65 mL)
was allowed to stir at ambient temperature for 20 h. The
solvent was removed under reduced pressure, and the
residue was purified by flash column chromatography
4.2.5. 2-[(4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-
4-methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-
3-methyl-4-hydroxy-but-2E-enoyl-oxy]-propane (4). Pre-
23
pared as described for compound 2. ½aꢁ 10.94 (c 3.1,
D
1
(EtOAc/MeOH, 9:1) to afford the title compound 1
CHCl3); IR (CHCl3, cast, cmꢀ1) 3412, 197, 1655; H
NMR (500 MHz, CDCl3) d 5.99 (s, 1H), 5.38–5.53 (m,
2H), 5.04 (septet, J = 6.3 Hz, 1H), 4.28 (d, J = 8.8 Hz,
1H), 3.96 (br s, 1H), 3.82–3.88 (m, 2H), 3.67 (dd,
J = 1.6, 9.4 Hz, 1H), 3.52–3.58 (m, 2H), 3.39 (d,
J = 5.5 Hz, 1H), 3.12 (d, J = 9.4 Hz, 1H), 3.01 (s, 1H),
2.20–2.35 (m, 6H), 1.82–1.88 (m, 1H), 1.26 (d,
J = 6.3 Hz, 6H), 1.16 (d, J = 6.2 Hz, 3H), 0.99 (d,
J = 6.9 Hz, 3H); 13C NMR (125 MHz, CDCl3) d 166.4,
157.8, 134.6, 129.1, 116.3, 75.9, 73.9, 71.4, 70.4, 67.1,
65.3, 64.7, 44.6, 41.5, 32.5, 22.0, 20.7, 16.8, 15.9; HRMS
(ESI, m/z) calcd for C20H34O7Na 409.21968, found
409.21960.
23
(27.0 mg, 90%) as a colorless oil. ½aꢁ 1.33 (c 1.4,
D
1
CHCl3); IR (CHCl3, cast, cmꢀ1) 3385, 1693, 1655; H
NMR (500 MHz, CD3OD) d 6.02 (s, 1H), 5.39–5.51
(m, 2H), 4.36 (s, 1H), 3.92 (dd, J = 3.0, 3.0 Hz, 1H),
3.82 (dd, J = 3.0, 9.5 Hz, 1H), 3.76 (dd, J = 2.6,
11.3 Hz, 1H), 3.68 (dd, J = 1.6, 9.5 Hz, 1H), 3.60 (dq,
J = 5.7, 5.7 Hz, 1H), 3.53 (d, J = 11.3 Hz, 1H), 3.41
(dd, J = 2.3, 8.4 Hz, 1H), 2.23–2.29 (m, 1H), 2.08–2.18
(m, 5H), 1.70–1.76 (m, 1H), 1.08 (d, J = 6.3 Hz, 3H),
0.98 (d, J = 6.9 Hz, 3H); 13C NMR (125 MHz, CD3OD)
d 170.5, 160.9, 135.7, 129.9, 116.6, 77.6, 74.4, 72.2, 71.9,
66.0, 65.8, 45.4, 43.9, 33.5, 20.3, 26.7, 16.2; HRMS (ESI,
m/z) calcd for C17H28O7Na 367.17273, found 367.17258.
4.2.6. (4R)-{(2S,3R,4R,5S)-3,4-O-Isopropylidene-3,4-
dihydroxy-5-[(4R,5S)-4-methyl-5-triisopropylsilyloxy-hex-
2-enyl]-tetrahydro-pyran-2-yl}-3-methyl-4-triisopropylsilyl-
oxy-but-2E-enoic acid butylamide (19). To a solution of
17 (0.220 g, 0.320 mmol) in CH2Cl2 (1.5 mL) at ambient
temperature were added sequentially PyBroP (0.180 g,
0.380 mmol) and butylamine (0.028 g, 0.380 mmol) fol-
lowed by Hunig’s base (0.130 g, 1.00 mmol). After being
stirred at ambient temperature overnight, the mixture
was diluted with EtOAc (30 mL) and washed with
H2O (10 mL) and brine (10 mL), dried over anhydrous
Na2SO4, filtered, concentrated, and purified by flash col-
4.2.3. (4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-4-
methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-3-
methyl-4-hydroxy-but-2E-enoyl-oxy-methane (2). To a
solution of compound 18 (0.130 g, 0.340 mmol) in
DMF (1.5 mL) at ambient temperature was added
KOSiMe3 (0.047 g, 0.370 mmol). After 10 min at ambi-
ent temperature, MeI (0.145 g, 1.00 mmol) was added.
The mixture was then stirred overnight at ambient tem-
perature. After that time, the mixture was diluted with
EtOAc (20 mL) and washed with H2O (10 mL) and
brine (10 mL), dried over anhydrous Na2SO4, filtered,
and concentrated to afford crude ester which was used
without purification.
umn chromatography (hexanes/EtOAc, 5:1) to afford 19
23
(0.195 g, 82%) as yellow oil. ½aꢁ 3.13 (c 0.3, CHCl3); IR
D
(CHCl3, cast, cmꢀ1) 3294, 1662, 1653; 1H NMR
(500 MHz, CDCl3) d 5.78 (s, 1 H), 5.59 (t, J = 5.5 Hz,
1H), 5.32–5.48 (m, 2H), 4.09–4.15 (m, 2H), 3.85–3.93
(m, 2H), 3.59–3.62 (m, 2H), 3.22–3.38 (m, 3H), 2.26–
2.32 (m, 1H), 2.16–2.22 (m, 2H), 2.05 (s, 3H), 1.90–
1.96 (m, 1H), 1.43–1.55 (m, 5H), 1.31–1.42 (m, 5H),
1.03–1.10 (m, 45H), 1.00 (d, J = 6.8 Hz, 3H), 0.93 (t,
J = 6.8 Hz, 3H); 13C NMR (125 MHz, CDCl3) d 167.1,
149.9, 135.7, 127.2, 120.3, 108.3, 80.2, 79.1, 75.6, 71.7,
71.0, 66.0, 44.1, 38.9, 36.8, 33.8, 31.8, 28.3, 26.4, 20.2,
19.2, 18.2, 18.2, 18.1, 18.0, 15.4, 14.1, 13.7, 12.6, 12.6;
HRMS (ESI, m/z) calcd for C42H82NO6Si2752.56752,
found 752.56731.
The ketal protecting group in the crude ester was re-
23
moved as described in the synthesis of 1. ½aꢁ 9.02 (c
D
0.57, CHCl3); IR (CHCl3, cast, cmꢀ1) 3420, 1705,
1655; 1H NMR (500 MHz, CDCl3) d 6.04 (s, 1H),
5.41–5.53 (m, 2H), 4.31 (s, 1H), 3.99 (br s, 1H), 3.85–
3.91 (m, 2H), 3.72 (s, 3H), 3.66 (dd, J = 2.0, 9.6 Hz,
1H), 3.53–3.59 (m, 2H), 3.41 (dd, J = 2.3, 8.4 Hz, 1H),
2.06–2.26 (m, 6H), 1.82–1.88 (m, 1H), 1.16 (d,
J = 6.2 Hz, 3H), 1.01 (d, J = 6.8 Hz, 3H); 13C NMR
(125 MHz, CDCl3) d 167.3, 158.7, 134.4, 129.0, 115.3,
75.8, 73.7, 71.4, 70.4, 65.3, 64.6, 51.1, 44.5, 41.5, 32.4,
20.6, 16.8, 16.0; HRMS (ESI, m/z) calcd for C18H31O7
[M+H] 359.20643, found 359.20673.
4.2.7. (4R)-{(2S,3R,4R,5S)-3,4-O-Isopropylidene-3,4-
dihydroxy-5-[(4R,5S)-4-methyl-5-triisopropylsilyloxy-hex-
2-enyl]-tetrahydro-pyran-2-yl}-3-methyl-4-triisopropylsilyl-
4.2.4. (4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-4-
methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-3-
methyl-4-hydroxy-but-2E-enoyl-oxy-ethane (3). Prepared
oxy-but-2E-enoic acid diethylamide (20). Prepared as de-
23
23
as described for compound 2. ½aꢁ 13.86 (c 3.1, CHCl3);
scribed for compound 19. ½aꢁ ꢀ9.65 (c 0.97, CHCl3);
D
D
IR (CHCl3, cast, cmꢀ1) 3419, 1700, 1653; 1H NMR
(500 MHz, CDCl3) d 6.02 (s, 1H), 5.36–5.52 (m, 2H),
4.30 (s, 1H), 4.16 (q, J = 7.1 Hz, 2H), 3.96 (br s, 1H),
3.82–3.89 (m, 2H), 3.66 (dd, J = 1.5, 9.5 Hz, 1H),
IR (CHCl3, cast, cmꢀ1) 2942, 1656, 1631; 1H NMR
(500 MHz, CDCl3) d 6.02 (s, 1H), 5.38–5.46 (m, 2H),
4.20 (d, J = 4.5 Hz, 1H), 4.08 (dd, J = 2.3, 5.0 Hz, 1H),
3.86–3.98 (m, 2H), 3.58–3.62 (m, 2H), 3.34–3.46 (m,

O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
1013
4H), 3.28 (dd, J = 4.3, 8.9 Hz, 1H), 2.26–2.32 (m, 1H),
2.16–2.22 (m, 2H), 1.88–2.00 (m, 4H), 1.46 (s, 3H),
1.32 (s, 3H), 1.12–1.16 (m, 51H), 1.00 (d, J = 6.9 Hz,
3H); 13C NMR (125 MHz, CDCl3) d 167.6, 146.7,
135.6, 127.2, 119.9, 108.3, 80.3, 78.7, 75.7, 71.7, 70.7,
65.8, 44.1, 36.9, 33.7, 28.3, 26.4, 19.2, 18.2, 18.1, 18.1,
18.1, 15.4, 14.1, 12.7, 12.6; HRMS (ESI, m/z) calcd for
C42H82NO6Si2 752.56752, found 752.56780.
(br s, 1H), 5.40–5.52 (m, 2H), 4.26 (s, 1H), 3.96 (s,
1H), 3.82–3.88 (m, 2H), 3.67 (d, J = 8.9 Hz, 1H), 3.52–
3.58 (m, 2H), 3.25–3.32 (m, 2H), 2.02–2.12 (m, 6H),
1.82–1.88 (m, 1H), 1.46–1.53 (m, 2H), 1.32–1.40 (m,
2H), 1.16 (d, J = 6.1 Hz, 3H), 1.00 (d, J = 6.7 Hz, 3H),
0.93 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3)
d 167.9, 151.2, 134.6, 128.8, 118.7, 76.2, 73.3, 71.3,
70.7, 65.0, 64.8, 44.4, 41.5, 39.2, 32.3, 31.6, 20.7, 20.2,
16.9, 15.5, 13.8; HRMS (ESI, m/z) calcd for
C21H38NO6 400.26936, found 400.26975.
4.2.8. (4R)-{(2S,3R,4R,5S)-3,4-O-Isopropylidene-3,4-
dihydroxy-5-[(4R,5S)-4-methyl-5-hydroxy-hex-2-enyl]-
tetrahydro-pyran-2-yl}-3-methyl-4-hydroxy-but-2E-enoic
acid butylamide (19-O-TIPS deprotected). To the solu-
tion of 19 (0.220 g, 0.235 mmol) in THF (3 mL) was
added TBAF (1.50 mL. 1.00 M solution in THF,
1.50 mmol). The reaction mixture was stirred at ambient
temperature for 11 h and quenched with a saturated
aqueous solution of NH4Cl (10 mL). The layers were
separated, and the aqueous layer was extracted with
EtOAc (2· 20 mL). The combined organic layers were
washed with water (20 mL) brine (20 mL), dried over
anhydrous Na2SO4, filtered, concentrated, and purified
by flash column chromatography (EtOAc/MeOH, 9:1)
4.2.11. (4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-4-
methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-3-
methyl-4-hydroxy-but-2E-enoic acid diethylamide (6).
23
Prepared as described for compound 1. ½aꢁ 25.39 (c
D
0.48, CHCl3); IR (CHCl3, cast, cmꢀ1) 3391, 1653,
1600; 1H NMR (500 MHz, CDCl3) d 6.18 (s, 1H),
5.39–5.53 (m, 2H), 4.25 (s, 1H), 3.95 (s, 1H), 3.86 (dd,
J = 2.5, 11.4 Hz, 1H), 3.83 (dd, J = 3.1, 9.6 Hz, 1H),
3.65 (dd, J = 2.8, 9.3 Hz, 1H), 3.52–3.58 (m, 2H),
3.36–3.50 (m, 5H), 2.06–2.26 (m, 3H), 1.86–1.91 (m,
4H), 1.12–1.19 (m, 9H), 0.99 (d, J = 6.9 Hz, 3H); 13C
NMR (125 MHz, CDCl3) d 169.2, 146.1, 134.3, 129.3,
119.0, 76.2, 73.3, 71.1, 70.6, 65.3, 64.9, 44.5, 42.8, 41.4,
39.5, 32.5, 20.4, 16.6, 15.7, 14.2, 13.0; HRMS (ESI, m/z)
calcd for C21H38NO6 400.26936, found 400.26975.
to afford the title compound 19-O-TIPS deprotected
23
(0.119 g, 81%) as a white foam. ½aꢁ ꢀ3.86 (c 0.84,
D
1
CHCl3); IR (CHCl3, cast, cmꢀ1) 3320, 1669, 1635; H
NMR (500 MHz, CDCl3) d 5.90 (s, 1H), 5.42–5.60 (m,
3H), 4.13–4.20 (m, 2H), 4.06 (s, 1H), 3.73 (dd, J = 1.7,
11.5 Hz, 1H), 3.66 (d, J = 11.5 Hz, 1H), 3.58 (t,
J = 6.1 Hz, 2H), 3.38–3.43 (m, 1H), 3.26–3.32 (m, 2H),
2.02–2.26 (m, 7H), 1.46–1.53 (m, 5H), 1.32–1.40 (m,
5H), 1.16 (d, J = 6.2 Hz, 3H), 1.02 (d, J = 6.8 Hz, 3H),
0.93 (t, J = 6.3 Hz, 3H); 13C NMR (125 MHz, CDCl3)
d 170.0, 150.6, 134.9, 128.9, 119.0, 108.7, 77.5, 75.7,
74.9, 71.1, 70.4, 66.4, 44.5, 39.0, 36.5, 34.1, 31.7, 28.3,
26.3, 20.5, 20.1, 16.7, 15.3, 13.7; HRMS (ESI, m/z) calcd
for C24H42NO6 440.30066, found 440.30006.
4.2.12. (R,2E)-ethyl 4-((2R,6S)-6-ethoxy-5,6-dihydro-
2H-pyran-2-yl)-4-hydroxy-3-methylbut-2-enoate (28). In
a flame-dried round-bottomed flask was placed a mix-
ture of 3-boronoacrolein pinacolate 11 (1.07 g,
5.88 mmol) (freshly distilled by Kugelrohr) and ethoxy-
ethene 21 (2 mL, 24.7 mmol). To this solution were
added the Jacobsen catalyst (1S,2R) 13 (100 mg,
0.21 mmol) and barium oxide powder (2.4 g). The reac-
tion mixture was allowed to stir at 20 ꢂC overnight and
then was directly purified to removed the catalyst
through a short chromatography column (Et3N deacti-
vated silica-gel, hexanes/ether 9:1). The desired com-
pound 23 (1.28 g) was obtained and was directly used
in the next reaction.
4.2.9. (4R)-{(2S,3R,4R,5S)-3,4-O-Isopropylidene-3,4-
dihydroxy-5-[(4R,5S)-4-methyl-5-hydroxy-hex-2-enyl]-
tetrahydro-pyran-2-yl}-3-methyl-4-hydroxy-but-2E-enoic
acid diethylamide (20-O-TIPS deprotected). Prepared as
23
D
described for compound 19-O-TIPS deprotected. ½aꢁ
A mixture of hetero Diels–Alder cycloadduct (1.28 g,
5.00 mmol) and the aldehyde 25 (2.0 g, 14.1 mmol) was
stirred at 50 ꢂC for 5 h in a sealed tube under nitrogen.
Upon completion, the mixture was cooled to ambient
temperature and a saturated aqueous NaHCO3 solution
(10 mL) was added to the reaction mixture, which was
stirred for 30 min. The resulting mixture was extracted
with ether. The ethereal layers were combined, washed
with brine and then dried over anhydrous MgSO4. After
filtration and concentration in vacuo, the residue was
purified by flash column chromatography (Et3N deacti-
vated silica-gel, hexane/EtOAc, 1:1) to yield 1.1 g (81%)
ꢀ12.89 (c 0.63, CHCl3); IR (CHCl3, cast, cmꢀ1) 3393,
1653, 1607; 1H NMR (500 MHz, CDCl3) d 6.16 (s,
1H), 5.45–5.57 (m, 2H), 4.18–4.22 (m, 2H), 4.10 (s,
1H), 3.74 (dd, J = 3.2, 11.7 Hz, 1H), 3.66 (d, J = 1.4,
11.7 Hz, 1H), 3.58 (dq, J = 6.3, 6.3 Hz, 1H), 3.35–3.43
(m, 5H), 2.18–2.26 (m, 2H), 2.08–2.12 (m, 1H), 2.02–
2.08 (m, 1H), 1.96 (s, 3H), 1.50 (s, 3H), 1.36 (s, 3H),
1.12–1.28 (m, 9H), 1.02 (d, J = 6.9 Hz, 3H); 13C NMR
(125 MHz, CDCl3) d 167.9, 146.3, 134.6, 129.0, 119.2,
108.5, 77.6, 75.7, 74.6, 71.0, 70.5, 66.5, 44.3, 42.4, 39.4,
36.6, 34.3, 28.3, 26.3, 20.4, 16.5, 15.4, 14.3, 13.1; HRMS
(ESI, m/z) calcd for C24H42NO6 440.30066, found
440.30033.
of the title compound 28 as a colorless oil. ½aꢁ25 +65.95 (c
D
2.42, CHCl3); IR (CHCl3, cast, cmꢀ1) 3444, 1714, 1654,
1
1377, 1215, 1149, 1061; H NMR (400 MHz, CDCl3) d
4.2.10. (4R)-{(2S,3R,4R,5S)-3,4-dihydroxy-5-[(4R,5S)-4-
methyl-5-hydroxy-hex-2-enyl]-tetrahydro-pyran-2-yl}-3-
6.02 (s, 1H), 5.62 (dq, J = 2.0, 10.2 Hz, 1H), 4.76 (dd,
J = 3.6, 6.0 Hz, 1H), 4.44 (m, 1H), 4.16 (q, J = 7.2 Hz,
2H), 4.01 (t, J = 5.4 Hz, 1H), 3.90 (dq, J = 7.2, 9.6 Hz,
1H), 3.52 (dq, J = 7.2, 9.4 Hz, 1H), 3.15 (d, J = 6.4 Hz,
1H), 2.22 (m, 5H), 1.28 (t, J = 7.0 Hz, 3H), 1.24 (t,
J = 7.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) d 166.7,
methyl-4-hydroxy-but-2E-enoic acid butylamide (5).
23
D
Prepared as described for compound 1. ½aꢁ 14.37 (c
0.16, CHCl3); IR (CHCl3, cast, cmꢀ1) 3346, 1667,
1
1634; H NMR (500 MHz, CDCl3) d 5.98 (s, 1H), 5.95

1014
O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
25
D
156.6, 125.9, 125.1, 117.4, 97.9, 78.1, 74.9, 64.7, 59.8,
30.6, 15.3, 15.1, 14.3; HRMS (EI, m/z) calcd for
C14H21O5 269.13889, found 269.13890.
compound 28-O-TIPS. ½aꢁ +38.78 (c 1.47, CHCl3);
IR (CHCl3, cast, cmꢀ1) 2944, 2868, 1720, 1216, 1149,
1112, 1047; 1H NMR (500 MHz, CDCl3) d 5.87 (s,
1H), 5.84 (ddd, J = 2.0, 6.0, 10.0 Hz, 1H), 5.64 (dt,
J = 1.2, 10.5 Hz, 1H), 4.58 (d, J = 2.5 Hz, 1H), 4.34
(m, 2H), 4.15 (q, J = 7.0 Hz, 2H), 3.88 (dq, J = 7.2,
9.8 Hz, 1H), 3.49 (m, 1H), 2.15 (d, J = 1.5 Hz, 2H),
2.07 (m, 1H), 1.66 (m, 1H), 1.23 (m, 16H), 1.07 (m,
21H), 0.87 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz,
CDCl3) d 166.7, 158.1, 130.4, 125.2, 117.5, 100.8, 78.9,
78.7, 64.1, 59.6, 39.3, 31.9, 29.8, 28.9, 27.1, 22.7, 18.0,
16.7, 15.3, 14.4, 14.1, 12.3; HRMS (EI, m/z) calcd for
C29H54O5Si 510.37405, found 510.37434.
4.2.13. (R,2E)-ethyl 4-((2R,5R,6S)–6-ethoxy-5-hexyl-5,6-
dihydro-2H-pyran-2-yl)-4-hydroxy-3-methylbut-2-enoate
(29). Prepared as described for compound 28. ½aꢁ25 +4.25
D
(c 2.62, CHCl3); IR (CHCl3, cast, cmꢀ1) 3418, 2927, 1716,
1214, 1150, 1044; 1H NMR (500 MHz, CDCl3) d 6.05 (t,
J = 2.0 Hz, 1H), 5.83 (dt, J = 3.0, 10.5 Hz, 1H), 5.62 (dt,
J = 2.0, 10.5 Hz, 1H), 4.72 (d, J = 3.5 Hz, 1H), 4.50 (m,
1H), 4.16 (dq, J = 1.5, 7.0 Hz, 2H), 3.97 (t, J = 5.3 Hz,
1H), 3.90 (dq, J = 7.0, 9.5 Hz, 1H), 3.48 (m, 2H), 2.24
(m, 1H), 2.18 (d, J = 1.5 Hz, 2H), 1.57 (m, 1H), 1.28 (m,
16H), 0.88 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz,
CDCl3) d 166.8, 157.1, 129.7, 124.9, 116.9, 98.9, 77.9,
74.3, 65.3, 59.7, 38.1, 31.8, 29.9, 29.5, 26.9, 22.7, 15.4,
14.9, 14.4, 14.1; HRMS (ESI, m/z) calcd for C20H34O5Na
377.22985, found 377.22963.
4.2.17. 3-((R)-1-((2R,6S)-6-ethoxy-5,6-dihydro-2H-pyr-
an-2-yl)-1-triisopropylsilyloxypropan-2-ylidene)-dihydro-
furan-2(3H)-one (30-O-TIPS) and (31-O-TIPS).
Prepared as described for compound 28-O-TIPS from
a mixture of 30 and 31 and obtained as a hard to sepa-
rate mixture. IR (CHCl3, cast, cmꢀ1) 2943, 2867, 1749,
1376, 1181, 1105, 1063, 1042, 1028; 1H NMR
(400 MHz, CDCl3) d 5.78 (m, 3H), 4.65 (m, 1H), 4.30
(m, 2H), 3.92 (m, 1H), 3.53 (m, 1H), 2.88 (m, 1H),
2.23 (t, J = 2.4, Hz, trans Me), 2.15 (m, 2H), 1.96 (t,
J = 1.8, Hz, cis Me), 1.27 (m, 5H), 1.06 (m, 21H);
HRMS (EI, m/z) calcd for C23H40O5Si 424.26450, found
424.26254.
4.2.14. 3-((R)-1-((2R,6S)-6-ethoxy-5,6-dihydro-2H-pyr-
an-2-yl)-1-hydroxypropan-2-ylidene)-dihydrofuran-2(3H)-
one (30) and (31). Prepared as described for compound
28 from a mixture of 26 and 27 and obtained as an
inseparable mixture. IR (CHCl3, cast, cmꢀ1) 3460,
1740, 1377, 1180, 1060, 1025; 1H NMR (400 MHz,
CDCl3) d 5.70 (m, 2H), 4.78 (m, 1H), 4.36 (m, 3H),
3.96 (m, 1H), 3.59 (m, 1H), 3.04 (m, 2H), 2.32 (t,
J = 2.4, Hz, trans Me), 2.26 (m, 2H), 2.03 (t,
J = 1.8, Hz, cis Me), 1.27 (m, 5H).
25
Cis compound 31-O-TIPS: ½aꢁ +31.11 (c 3.22, CH2Cl2);
D
IR (microscope, cmꢀ1) 2943, 2866, 1746, 1185, 1106,
1
1061, 1042, 1028; H NMR (300 MHz, CHCl3) d 6.25
4.2.15. (R,2E)-ethyl 4-((2R,6S)-6-ethoxy-5,6-dihydro-
2H-pyran-2-yl)-4-triisopropylsilyloxy-3-methylbut-2-eno-
ate (28-O-TIPS). To a solution of alcohol 28 (1.00 g,
3.70 mmol) and 2,6-lutidine (1.19 g, 11.10 mmol) in
dichloromethane (20 mL) at 0 ꢂC was added triisopropyl-
silyl trifluoromethanesulfonate (2.27 g, 7.40 mmol). The
reaction mixture was allowed to slowly warm to room
temperature and was left to react overnight. An aqueous
saturated NaHCO3 solution (10 mL) was added and the
reaction mixture was stirred for another 30 min. The lay-
ers were separated and the aqueous layer was extracted
with CH2Cl2 (2· 100 mL). The combined organic layers
were washed with brine (50 mL), dried over anhydrous
Na2SO4, filtered, concentrated, and purified by flash col-
umn chromatography (Et3N deactivated silica-gel, pen-
(d, J = 5.7 Hz, 1H), 5.75 (m, 2H), 4.62 (dd, J = 4.0,
8.0 Hz, 1H), 4.35 (m, 3H), 3.91 (dq, J = 7.2, 9.8 Hz,
1H), 3.49 (dq, J = 7.2, 9.5 Hz, 1H), 2.86 (t, J = 7.0 Hz,
2H), 2.12 (m, 3H), 1.90 (t, J = 1.8 Hz, 3H), 1.20 (t,
J = 7.1 Hz, 2H), 1.06 (m, 21H); 13C NMR (100 MHz,
CHCl3) d 153.7, 130.6, 127.1, 124.3, 120.5, 98.7, 77.8,
69.1, 64.6, 63.9, 31.4, 28.1, 18.2, 17.9, 15.4, 12.5; HRMS
(ESI, m/z) calcd for C23H40O5SiNa 447.25372, found
447.25328.
4.2.18. (R,2E)-ethyl 4-((R)-5,6-dihydro-2H-pyran-2-yl)-4-
triiso-propylsilyloxy-3-methylbut-2-enoate (32). To
a
solution of pyran 28-O-TIPS (0.80 g, 1.88 mmol) and
triethylsilane (0.87 g, 7.50 mmol) in CH2Cl2 (10 mL)
was added TiCl4 (2.44 mL, 1.0 M solution in CH2Cl2,
2.44 mmol) dropwise at ꢀ50 ꢂC. After being stirred for
2.5 h at ꢀ50 ꢂC, the reaction mixture was allowed to
warm up to ambient temperature and quenched with
aqueous saturated NaHCO3 solution (3 mL). The layers
were separated and the aqueous layer was extracted with
CH2Cl2 (2· 15 mL). The combined organic layers were
washed with brine (15 mL), dried over anhydrous
Na2SO4, filtered, concentrated, and purified by flash col-
umn chromatography (hexanes/EtOAc 7:3) to afford the
tane/ether, 9:1) to yield 1.5 g of the title compound 28-
25
O-TIPS (yield 95%) as colorless oil. ½aꢁ +97.78 (c 2.45,
D
CHCl3); IR (CHCl3, cast, cmꢀ1) 2944, 2868, 1719, 1216,
1144, 1108, 1063; 1H NMR (400 MHz, CDCl3) d 5.91 (s,
1H), 5.72 (m, 1H), 5.64 (dq, J = 1.6, 10.0 Hz, 1H), 4.62
(q, J = 3.4 Hz, 1H), 4.38 (m, 2H), 4.16 (q, J = 7.0 Hz,
2H), 3.95 (dq, J = 7.2, 9.6 Hz, 1H), 3.54 (dq, J = 7.2,
9.6 Hz, 1H), 2.15 (d, J = 1.2 Hz, 3H), 2.13 (m, 2H), 1.29
(t, J = 7.2 Hz, 3H), 1.24 (t, J = 7.2 Hz, 3H), 1.07 (m,
21H); 13C NMR (100 MHz, CDCl3) d 166.8, 158.2,
125.9, 124.6, 117.2, 99.0, 78.6, 63.9, 59.6, 31.3, 18.0,
17.8, 16.5, 15.3, 14.4, 12.4; HRMS (EI, m/z) calcd for
C23H42O5Si 426.28015, found 426.28069.
title compound 32 (0.71 g, 98% yield) as a yellow oil.
25
½aꢁ +61.62 (c 2.11, CHCl3); IR (CHCl3, cast, cmꢀ1
)
D
2944, 2867, 1719, 1217, 1152, 1107, 883; 1H NMR
(400 MHz, CDCl3) d 5.9 (m, 2H), 5.70 (dq, J = 1.6,
10.4 Hz, 1H), 4.31 (d, J = 5.6 Hz, 1H), 4.25 (m, 1H),
4.15 (q, J = 7.2 Hz, 2H), 3.92 (m, 1H), 3.63 (ddd,
J = 4.0, 9.2, 11.0 Hz, 1H), 2.2 (m, 1H), 2.14 (d,
J = 1.6 Hz, 3H), 1.9 (m, 1H), 1.28 (t, J = 7.2 Hz, 3H),
4.2.16. (R,2E)-ethyl 4-((2R,5R,6S)-6-ethoxy-5-hexyl-5,6-
dihydro-2H-pyran-2-yl)-4-triisopropylsilyloxy-3-methyl-
but-2-enoate (29-O-TIPS). Prepared as described for

O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
1015
1.06 (m, 21H); 13C NMR (100 MHz, CDCl3) d 166.9,
158.5, 126.3, 126.1, 117.1, 78.8, 63.4, 59.6, 25.3, 18.0,
17.8, 16.5, 14.4, 12.4; HRMS (ESI, m/z) calcd for
C21H38O4SiNa 405.24316, found 405.24318.
compound dihydroxy-32 (0.50 g, 91%) as a colorless
25
oil. ½aꢁ +14.44 (c 1.08, CHCl3); IR (CHCl3, cast,
D
cmꢀ1) 3486, 2945, 2869, 1718, 1216, 1155, 1096, 883;
1H NMR (400 MHz, CDCl3) d 6.07 (s, 1H), 4.55 (d,
J = 4.4 Hz, 1H), 4.18 (dq, J = 1.2, 7.2 Hz, 2H), 4.03
(q, J = 3.2 Hz, 1H), 3.99 (s, 1H), 3.83 (dd, J = 4.0,
9.6 Hz, 1H), 3.75 (dt, J = 2.8, 11.6 Hz, 1H), 3.66 (ddd,
J = 1.4, 5.4, 11.2 Hz, 1H), 3.57, (dd, J = 3.0, 9.9 Hz,
1H), 2.68 (d, J = 1.6 Hz, 1H), 2.21 (d, J = 1.2 Hz, 3H),
1.80 (m, 1H), 1.74 (m, 1H), 1.29 (t, J = 7.2 Hz, 3H),
1.15 (m, 3H), 1.06 (t, J = 6.6 Hz, 18H); 13C NMR
(100 MHz, CDCl3) d 166.8, 157.1, 117.6, 78.8, 76.0,
69.7, 66.3, 62.5, 60.0, 30.7, 18.2, 18.0, 14.5, 12.3; HRMS
(EI, m/z) calcd for C21H40O6Si 426.25942, found
426.25026.
4.2.19. (R,2E)-ethyl 4-((2R,5R)-5-hexyl-5,6-dihydro-2H-
pyran-2-yl)-4-triisopropylsilyloxy-3-methylbut-2-enoate
25
(33). Prepared as described for compound 32. ½aꢁ
D
+27.93 (c 1.42, CHCl3); IR (CHCl3, cast, cmꢀ1) 2928,
2867, 1720, 1215, 1182, 1008; 1H NMR (500 MHz,
CDCl3) d 5.87 (m, 2H), 5.69 (dt, J = 1.7, 10.0 Hz, 1H),
4.31 (d, J = 5.5 Hz, 1H), 4.22 (m, 1H), 4.16 (q,
J = 7.0 Hz, 2H), 3.66 (m, 2H), 2.15 (d, J = 1.5 Hz,
2H), 1.94 (m, 1H), 1.29 (m, 14H), 1.07 (m, 21H), 0.89
(t, J = 7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) d
166.7, 158.3, 131.0, 125.3, 117.4, 78.9, 77.5, 67.4, 59.6,
34.7, 33.3, 31.8, 29.5, 27.2, 22.7, 18.0, 16.6, 14.4, 14.1,
12.4; HRMS (EI, m/z) calcd for C27H50O4Si
466.34784, found 466.34809.
4.2.23. (R,E)-ethyl 4-((2S,3R,4R,5S)-5-hexyl-tetrahydro-
3,4-di-hydroxy-2H-pyran-2-yl)-4-triisopropylsilyloxy-3-
me-thylbut-2-enoate (dihydroxy-33). Prepared as de-
25
scribed for compound dihydroxy-32. ½aꢁ +37.19 (c
D
4.2.20. (3E)-dihydro-3-((R)-1-((R)-5,6-dihydro-2H-pyran-
2-yl)-1-triisopropylsilyloxypropan-2-ylidene)furan-2(3H)-
0.63, CHCl3); IR (CHCl3, cast, cmꢀ1) 3485, 2929,
2868, 1719, 1215, 1154, 1094, 1047; 1H NMR
(400 MHz, CDCl3) d 6.08 (t, J = 1.2 Hz, 1H), 4.55 (d,
J = 4.0 Hz, 1H), 4.15 (m, 3H), 3.84 (s, 1H), 3.81 (m,
1H), 3.73 (s, 1H), 3.66 (dd, J = 3.2, 10.0 Hz, 1H), 3.54
(d, J = 11.6 Hz, 1H), 2.72 (s, 1H), 2.21 (d, J = 1.2 Hz,
2H), 1.72 (m, 1H), 1.27 (m, 14H), 1.09 (m, 21H), 0.87
(t, J = 7.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) d
166.6, 157.1, 117.2, 78.5, 70.2, 66.7, 65.6, 59.8, 40.3,
31.7, 29.3, 28.7, 27.6, 22.6, 18.04, 19.95, 17.5, 14.3,
14.1, 12.1; HRMS (ESI, m/z) calcd for C27H52O6SiNa
523.34254, found 523.34233.
25
D
one (34). Prepared as described for compound 32. ½aꢁ
ꢀ1.29 (c 0.97, CHCl3); IR (CHCl3, cast, cmꢀ1) 2944,
2867, 1753, 1375, 1183, 1101, 1068, 1038, 1014, 883;
1H NMR (400 MHz, CHCl3) d 5.90 (m, 1H), 5.79 (dd,
J = 3.8, 8.2 Hz, 1H), 4.56 (d, J = 6.4 Hz, 1H), 4.27 (m,
3H), 3.85 (m, 1H), 3.62 (m, 1H), 3.05 (m, 1H), 2.88
(m, 1H), 2.22 (t, J = 2.2 Hz, 3H), 2.17 (m, 1H), 1.94
(m, 1H), 1.07 (m, 21H); 13C NMR (100 MHz, CHCl3)
d 170.8, 152.7, 126.5, 126.0, 120.4, 77.5, 75.9, 64.7,
63.0, 28.0, 25.3, 18.0, 12.4, 5.9; HRMS (EI, m/z) calcd
for C21H36O4Si 380.23828, found 380.23831.
4.2.24. (3E)-dihydro-3-((R)-1-((2S,3R,4R)-tetrahydro-
3,4-dihydroxy-2H-pyran-2-yl)-1-triisopropylsilyloxy-pro-
pan-2-ylidene)furan-2(3H)-one (dihydroxy-34). Prepared
4.2.21. (3Z)-dihydro-3-((R)-1-((R)-5,6-dihydro-2H-pyr-
an-2-yl)-1-triisopropylsilyloxypropan-2-ylidene)furan-
2(3H)-one (35). Prepared as described for compound 32.
25
as described for compound dihydroxy-32. ½aꢁ ꢀ6.90
D
25
½aꢁ +23.08 (c 1.92, CH2Cl2); IR (microscope, cmꢀ1
)
(c 1.15, CHCl3); IR (CHCl3, cast, cmꢀ1) 3461, 2945,
2868, 1732, 1184, 1099, 1058, 1038, 1015; 1H NMR
(500 MHz, CHCl3) d 4.84 (d, J = 4.5 Hz, 1H), 4.28 (m,
2H), 4.18 (s, 1H), 4.07 (q, J = 3.0 Hz, 1H), 3.89 (dd,
J = 4.5, 10.0 Hz, 1H), 3.76 (dt, J = 3.0, 11.7 Hz, 1H),
3.63 (m, 2H), 3.14 (m, 1H), 2.82 (m, 1H), 2.64 (d,
J = 1.0 Hz, 1H), 2.39 (t, J = 2.2 Hz, 3H), 1.79 (m, 2H),
1.13 (m, 21H); 13C NMR (125 MHz, CHCl3) d 170.6,
149.9, 122.7, 76.8, 76.1, 70.3, 66.2, 64.8, 62.3, 32.7,
30.5, 28.1, 17.9, 12.1; HRMS (ESI, m/z) calcd for
C21H38O6SiNa 437.23299, found 437.23286.
D
2943, 2866, 1745, 1183, 1102, 1086, 1063, 1042; 1H
NMR (500 MHz, CHCl3) d 6.19 (d, J = 5.5 Hz, 1H),
5.92 (m, 1H), 5.69 (dq, J = 2.0, 10.5 Hz, 1H), 4.35 (t,
J = 7.3 Hz, 2H), 4.22 (m, 1H), 4.04 (quint, J = 5.5 Hz,
1H), 3.70 (quint, J = 5.5 Hz, 1H), 2.89 (t, J = 7.5 Hz,
2H), 2.09 (m, 2H), 1.96 (t, J = 1.5 Hz, 3H), 1.10 (m,
21H); 13C NMR (125 MHz, CHCl3) d 169.5, 154.7,
126.9, 126.4, 119.8, 77.3, 70.2, 64.7, 62.3, 27.9, 25.2,
18.0, 17.6, 12.5; HRMS (ESI, m/z) calcd for C21H36O4S-
iNa 403.22751, found 403.22818.
4.2.22. (R,E)-ethyl 4-((2S,3R,4R)-tetrahydro-3,4-dihy-
droxy-2H-pyran-2-yl)-4-triisopropylsilyloxy-3-methylbut-
2-enoate (dihydroxy-32). The pyran 32 (0.50 g,
1.31 mmol) was dissolved in acetone/water (60 mL,
9:1). Then, the monohydrate of N-methylmorpholine
N-oxide (0.23 g, 1.96 mmol) and osmium tetroxide
(2.5 wt% solution in 2-methyl-2-propanol, 0.7 mL) were
added and the mixture was stirred at ambient tempera-
ture overnight. It was then diluted with aqueous sodium
sulfite (50 mL) and extracted with EtOAc (2· 200 mL).
The combined organic layers were washed with water
(100 mL) and brine (100 mL), dried over anhydrous
Na2SO4, filtered, concentrated, and purified by flash col-
umn chromatography (EtOAc 100%) to afford the title
4.2.25. (R,E)-ethyl 4-((2S,3R,4R)-tetrahydro-3,4-dihy-
droxy-2H-pyran-2-yl)-4-hydroxy-3-methylbut-2-enoate
25
(7). Prepared as described for compound 1. ½aꢁ ꢀ14.07
D
(c 0.63, CHCl3); IR (CHCl3, cast, cmꢀ1) 3421, 2929,
2878, 1703, 1218, 1157, 1137, 1112, 1078, 1046, 757;
1H NMR (400 MHz, acetone-d6) d 6.02 (s, 1H), 4.32
(d, J = 8.0 Hz, 1H), 4.09 (q, J = 7.2 Hz, 2H), 4.07 (m,
1H), 3.86 (m, 1H), 3.76 (d, J = 8.4 Hz, 1H), 3.69 (m,
3H), 3.55 (ddd, J = 2.0, 4.9, 10.9 Hz, 1H), 2.79 (s, 1H),
2.11 (s, 3H), 1.73 (m, 2H), 1.22 (t, J = 7.2 Hz, 3H);
13C NMR (100 MHz, acetone-d6) d 167.1, 161.0, 115.7,
76.8, 74.2, 68.2, 67.8, 62.3, 59.7, 33.2, 16.1, 14.6; HRMS
(ESI, m/z) calcd for C12H20O6Na 283.11521, found
283.11520.

1016
O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
4.2.26.
(3E)-dihydro-3-((R)-1-((2S,3R,4R)-tetrahydro-
colonies were inoculated into 4 ml trypticase soy broth
and grown about five hours, standing, at 35 ꢂC. Cultures
were adjusted to A625 of 0.1 (0.5 McFarland’s Standard)
and streaked on Mueller–Hinton agar plates using a
sterile cotton swab. All compounds were dissolved in
25% methanol in water. Disks were loaded with com-
pounds in 15 ll of the appropriate solvents as indicated
and placed on the agar plates. Plates were incubated for
about 17 h at 35 ꢂC and zones of inhibition were re-
corded. All plates were done in duplicate for each S. aur-
eus strain. One representative set of data is shown.
3,4-dihydroxy-2H-pyran-2-yl)-1-hydroxypropan-2-ylidene)-
furan-2(3H)-one (8). To the solution of the TIPS
protected alcohol dihydroxy-34 (0.04 g, 0,096 mmol) in
THF (8 mL) were added acetic acid (0.01 g, 0.16 mmol)
and TBAF (1 M solution in THF, 0.096 mL,
0.096 mmol). The reaction mixture was stirred at rt for
20 h. Upon completion, the solvent was evaporated in
vacuo and the residue was used directly purified by flash
chromatography (EtOAc/MeOH, 9:1) to yield the title
25
compound 8 as a white solid (25 mg, 100% yield). ½aꢁ
D
ꢀ60.70 (c 0.42, MeOH); IR (CHCl3, cast, cmꢀ1) 3310,
1
1723, 1181, 1071, 1020; H NMR (500 MHz, CD3OD)
d 4.60 (s, 1H), 4.30 (m, 2H), 4.08 (m, 1H), 3.68 (m,
3H), 3.55 (dd, J = 2.0, 9.5 Hz, 1H), 2.97 (m, 2H), 2.26
(t, J = 2.3 Hz, 3H), 1.85 (tdd, J = 2.5, 5.5, 12.0 Hz,
1H), 1.72 (dq, J = 1.7, 14.0 Hz, 1H); 13C NMR
(100 MHz, CD3OD) d 173.5, 157.7, 119.3, 79.1, 72.1,
68.43, 68.39, 66.4, 62.8, 33.6, 28.0, 14.5; HRMS (ESI,
m/z) calcd for C12H18O6Na 281.09956, found 281.09970.
Acknowledgments
This work was funded by the Natural Sciences and Engi-
neering Research Council (NSERC) of Canada. X.G.
thanks the University of Alberta for a Province of Al-
berta Graduate Fellowship. The authors thank Dr. R.
McDonald and Dr. M. Ferguson for the X-ray crystal-
lographic analysis of compound 8.
4.2.27. (3Z)-dihydro-3-((R)-1-((2S,3R,4R)-tetrahydro-3,4-
dihydroxy-2H-pyran-2-yl)-1-hydroxypropan-2-ylidene)-
furan-2(3H)-one (9). The dihydroxy pyran was prepared
as described in the synthesis of dihydroxy-32 and was di-
Supplementary data
rectly in the next reaction. The TIPS deprotection was
Procedure for the preparation of 22, 26, and 27: struc-
25
1
D
tures of additional synthetic intermediates; H and 13C
achieved as described for compound 8. ½aꢁ ꢀ6.90 (c
1.15, CHCl3); IR (CHCl3, cast, cmꢀ1) 3315, 2974,
2918, 2880, 1723, 1650, 1182, 1071, 1022, 921; 1H
NMR (400 MHz, acetone-d6) d 5.78 (s, 1H), 4.32 (dt,
J = 1.6, 4.5 Hz, 2H), 4.10 (m, 1H), 3.89 (d, J = 8.4 Hz,
1H), 3.72 (m, 2H), 3.55 (dd, J = 2.0, 9.5 Hz, 1H), 3.45
(m, 2H), 1.93 (t, J = 2.3 Hz, 3H), 1.85 (m, 1H), 1.72
(m, 1H); 13C NMR (100 MHz, acetone-d6) d 170.6,
157.2, 120.0, 80.4, 68.4, 67.9, 67.6, 65.7, 62.2, 33.0,
29.4, 18.4; HRMS (EI, m/z) calcd for C12H14O4
222.08920, found 222.08933.
NMR spectra for compounds 1–10 and crystallographic
data for compound 8 (CCDC #668593) are provided.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.bmc.2008.
01.001.
References and notes
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3,4-di-hydroxy-2H-pyran-2-yl)-4-hydroxy-3-methylbut-2-
25
enoate (10). Prepared as described for compound 1. ½aꢁ
D
ꢀ4.82 (c 0.99, MeOH); IR (CHCl3, cast, cmꢀ1) 3496,
3365, 2926, 2896, 1717, 1214, 1155, 1045; 1H NMR
(400 MHz, CDCl3) d 6.01 (t, J = 1.4 Hz, 1H), 4.28 (d,
J = 9.2 Hz, 1H), 4.16 (q, J = 7.2 Hz, 2H), 3.97 (m,
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4.3. Bioassay24
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O. Marion et al. / Bioorg. Med. Chem. 17 (2009) 1006–1017
1017
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´
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