Synthesis of structurally simplified aureolic acid aglycone-C-D-E trisaccharide analogues

Article abstract of DOI:10.1071/CH01198

Syntheses of aureolic acid analogues (5) and (6) with (2S)- and (2R)-acyloin stereochemistry, respectively, are described. The synthesis of (5) utilizes a 'C + DE' glycosidation sequence, whereas analogue (6), with unnatural (2R)-acyloin stereochemistry, was synthesized by a sequence in which the entire C-D-E trisaccharide was introduced in a single step. While these syntheses provided sufficient quantities of the two aureolic acid analogues for use in studies of Mg²⁺ complex formation and deoxyribonucleic acid (DNA) binding, this work also highlights certain limitations in the use of 2-thiophenyl glycosyl donors for synthesis of 2-deoxy-β-glycosides. Specifically, difficulties were encountered in the identification of a protecting group for the aglycone C8 phenol that is fully compatible with the conditions required for reductive removal of the thiophenyl substituents after completion of the glycosidation sequence. Sensitivity of the C2 acyloin stereocentre to the conditions required for deprotection of a phenolic acetate ester are also highlighted in the syntheses of (5), and especially of (6).

Full text of DOI:10.1071/CH01198

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Aust. J. Chem. 2002, 55, 113–121
Synthesis of Structurally Simplified Aureolic Acid
Aglycone-C–D–E Trisaccharide Analogues
William R. Roush,A,B Noel A. PowellA and Ray A. JamesA
A Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, U.S.A.
B Author to whom correspondence should be addressed (e-mail: roush@umich.edu).
Syntheses of aureolic acid analogues (5) and (6) with (2S)- and (2R)-acyloin stereochemistry, respectively, are
described. The synthesis of (5) utilizes a ‘C + DE’ glycosidation sequence, whereas analogue (6), with unnatural
(2R)-acyloin stereochemistry, was synthesized by a sequence in which the entire C–D–E trisaccharide was
introduced in a single step. While these syntheses provided sufficient quantities of the two aureolic acid analogues
for use in studies of Mg2+ complex formation and deoxyribonucleic acid (DNA) binding, this work also highlights
certain limitations in the use of 2-thiophenyl glycosyl donors for synthesis of 2-deoxy-β-glycosides. Specifically,
difficulties were encountered in the identification of a protecting group for the aglycone C8 phenol that is fully
compatible with the conditions required for reductive removal of the thiophenyl substituents after completion of the
glycosidation sequence. Sensitivity of the C2 acyloin stereocentre to the conditions required for deprotection of a
phenolic acetate ester are also highlighted in the syntheses of (5), and especially of (6).
Manuscript received: 1 December 2001.
Final version: 8 March 2002.
C
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01198
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A
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s
Introduction
MeO
HO
Me
O
AcO
Me
Olivomycin A(1), chromomycin A3 (2) and mithramycin (3)
are well known members of the aureolic acid family of
antitumour antibiotics.[1–3] Mithramycin (3) has been used
clinically in the U.S. for treatment of testicular tumours,
while chromomycin A3 has been used in Japan in
combination with mitomycin C and 5-fluorouracil for
treatment of solid tumours, particularly advanced stomach
cancers.[2] The aureolic acids are inhibitors of
DNA-dependent ribonucleic acid (RNA) polymerase, and
bind in the minor groove of double stranded DNA as 2:1
OMe OH
O
H
B
O
O
Me
A
O
OH
R1
O
OH OH
Me
O
Me
O
O
HO
HO
O
O
Me
Me
R2CO2
D
C
O
OH
(1) olivomycin A (R1 = H, R2 = i-Pr)
(2) chromomycin A3 (R1 = R2 = Me)
E
Me
Me
OMe OH
O
O
H
HO
HO
HO
antibiotic/Mg2+
complexes
with
selectivity
for
O
Me
O
B
A
guanine/cytosine (GC)-rich sequences.[4–7] Under certain
conditions (low Mg2+ concentration), a 1:1 complex has also
been detected.[8,9] Mithramycin binds to the GC-rich
promoter regions of the c-myc protooncogene and the
dihydrofolate-reductase gene, thereby preventing their
translation.[10,11]
O
OH
Me
O
OH OH
Me
O
HO
Me
Me
OH
O
O
O
HO
HO
Me
O
O
E
D
C
(3) mithramycin
The aureolic acid antibiotics have attracted considerable
attention in view of the role played by the oligosaccharide
units in DNA binding, Mg2+ complex formation, and the
biological manifestations of these properties.[12–17] Nuclear
magnetic resonance (NMR) studies by Patel[4,5] and
Kahne[13,14] have established that the C–D disaccharide of
one monomer stacks on the aromatic nucleus of the other
aglycone in the 2:1 complexes with Mg2+, both when bound
to DNA,[4,5] and when free in MeOH solution.[13,14] The
intact C–D–E trisaccharide is essential for stable dimer
formation (in MeOH)[13,14] and maximal DNA binding,[18,19]
as well as for full activity as an antitumour agent.[1–3]
However, the roles played by the A–B disaccharide and the
C3 polyoxygenated side chain in the DNA binding event
have not been delineated. Kahne has demonstrated that
aureolic acid analogue (4), containing a triethylene glycol
mimic of the C–D–E trisaccharide, forms a 2:1 complex
with Mg2+, but DNA-binding data have not been
reported.[15,16]
© CSIRO 2002
10.1071/CH01198
0004-9425/02/010113

114
W. R. Roush, N. A. Powell and R. A. James
As part of a program aimed at defining the minimal
55 psi H2
Raney nickel
AcCl, pyridine
structural requirements for DNA binding by the aureolic acid
antibiotics, we targeted the synthesis of the simplified
analogues (5) and (6) lacking the A–B disaccharide and C3
side chain. We report herein the syntheses of (5) and (6).
Studies of Mg2+ complex formation and DNA-binding
properties of these analogues are being performed in
collaboration with Professor D. Kahne of Princeton
University, and will be reported in due course.
CH2Cl2, 23˚C
90%
1 M NaOH
89%
OH OH OH
(7)
OH OH
(8)
O
AcO
OH
(9)
O
Pseudomonas
fluorescens lipase (PFL)
1) TMSOTf, Et3N,
CH2Cl2, 78˚C
2) m-CPBA, NaHCO3
CH2Cl2, –78 to 0˚C
vinyl acetate, 23˚C
OH
AcO
OH
O
81%
rac-(10)
1) PFL, pH 7 buffer
+
2) Ac2O, CH2Cl2,
pyridine, 0˚C
70% (2 steps)
OH
OH
OAc
AcO
OH
O
AcO
OH
O
AcO
OH
O
(2S)
(R)-(+)-(10), 97% ee
[α]D25 +48.9˚
(S)-(–)-(10), 47%
95% ee, [α]D24 –44.9˚
(c 1.05, CHCl3)
(R)-(+)-(11) 48%
[α]D25 +154.1˚
O
O
OH OH
O
OH OH
Me
O
(c 0.72, CHCl3)
(c 1.19, CHCl3)
O
O
O
Me
Ac2O, pyridine
Me
O
O
O
HO
HO
O
(R)-(+)-(11)
O
(4)
Me
OH
CH2Cl2, 0˚C
85%
OAc
Me
i-PrCO2
D
C
O
HO
OH
O
(5) (2S)-epimer
(6) (2R)-epimer
E
(R)-(12)
Scheme 1. Synthesis of glycosidation substrates (S)-(10) and
(R)-(10).
Results and Discussion
Synthesis of Analogue (5)
1) NH3, MeOH
2) Bu3SnH
The aglycon unit of analogue (5) was synthesized from
anthralin (7) by using modifications of the sequence reported
by Kahne.[15,16] Raney nickel (RaNi) catalysed
hydrogenation of (7) gave diphenolic ketone (8) (Scheme 1).
We found it advantageous to protect the C8 phenol of (8) in
order to improve the handling characteristics of the air- and
acid-sensitive ketone and subsequent intermediates. In early
stages of this work, we protected (8) as a benzyloxymethyl
(BOM) ether [see (13), Scheme 2] and elaborated this
intermediate to the protected trisaccharide conjugate (14) by
using the glycosidation chemistry employed in our synthesis
3) RaNi, THF,
O
EtOH
38 50%
BOMO
ClAc
OH
Br
O
BOMO
OH
O
Br
(13)
O
O
O
O
ClAcO
O
Me
O
SPh
SPh
Me
i-PrCO2
(14)
OH
I
O
RO
OH
Me
O
Me
O
O
HO
HO
O
O
Me
Me
i-PrCO2
O
RaNi or
H2, Pd/C
(15) R = BOM
(6) R = H
of
olivomycin
A.[20]
However,
while
mild
OH
dechloroacetylation of (14) followed by Bu3SnH reduction
of the three halogen substituents and RaNi reduction of the
two thiophenyl groups provided a route to (15), all attempts
to remove the C8 BOM-ether protecting group by
hydrogenation protocols were unsuccessful. Although we
were able to obtain 1H NMR and mass spectroscopic
evidence for production of (6) in RaNi reductions of (15),
mass recoveries were always extremely poor and we were
never able to isolate research quantities of (6) with
acceptable purity. We attributed these difficulties to the
propensity of (6) to bind to metal ions (or surfaces). Similar
issues were encountered in the final stages of our olivomycin
A total synthesis,[20] a problem that we circumvented by
adjusting the physical properties of the substrate for the RaNi
reduction by incorporation of several silyl ether protecting
groups earlier in the synthesis. Regrettably, similar tactics
were not successful in our efforts to synthesize (6) from
precursors (14) and (15).
Scheme 2. Synthesis of BOM-protected trisaccharide conjugate
(15).
the intermediate enol silane.[21–23] Enzymatic resolution of
racemic (10) using Pseudomonas fluorescens lipase (PFL) in
vinyl acetate provided alcohol (S)-(10) and the enantiomeric
diacetate
(R)-(11)
with
almost
perfect
enantioselectivity.[15,16] Deacylation of (11) was performed
using PFL in aqueous buffer to prevent racemization of the
acyloin centre. However, under these conditions the C8
phenolic acetate was also hydrolysed.[24] The C8 acetate was
easily reinstalled selectively by using Ac2O and pyridine in
CH2Cl2, thereby providing (R)-(10) in good overall yield
with no loss of enantiomeric purity. The enantiomeric purity
of alcohols (S)- and (R)-(10) was assessed by using the
Mosher ester analysis,[25] and their absolute configurations
were confirmed by conversion of (R)-(12), which was
prepared by PFL-mediated resolution of the diphenol
corresponding to rac-(10),[15,16] into the diacetate (R)-(11). It
should be noted that the stereochemistry of these
intermediates reflects the recently reassigned stereostructure
of (R)-(12).[26]
After consideration of other protecting groups for the C8
phenolic unit, we settled on the use of an acetate ester for
these purposes. Thus, acylation of (8) with acetyl chloride
and pyridine provided monoacetate (9) in excellent yield
(Scheme 1). This intermediate was readily converted into
racemic α-hydroxy ketone (10) by Rubottom oxidation of

Synthesis of Structurally Simplified Aureolic Acid Analogues
115
entailed use of 0.3 equiv. of tert-butyldimethylsilyl triflate
(TBSOTf) as the promoter at –15°C. Lower reaction
temperatures and/or use of TMSOTf resulted in the
exclusive formation of (21) and (22). This example adds to
the growing list of cases in which TBSOTf has proven
superior to TMSOTf for glycosidations of sensitive
substrates.[20,31,32]
OH
AcO
OH
rac-(10)
O
Br
O
ClAcO
TESO
AcO
OH
Br
O
AcO
OH
Br
O
TMSOTf, CH2Cl2
4 Å sieves
–78˚C
O
O
PhS
O
NH
CCl3
(16)
O
O
ClAcO
TESO
ClAcO
TESO
PhS
(17) 30%
PhS
(18) 34%
(S)-(10), TMSOTf
4 Å sieves CH2Cl2, –78˚C
The fully elaborated trisaccharide (23) was readily
converted into analogue (5) by a three-step sequence. The
chloroacetyl (ClAc) groups were removed selectively by
treating (23) with methanolic NH3 in CH2Cl2 at 0°C to
provide diol (24). Cleavage of the phenolic acetate group was
avoided by stopping the reaction at 50% conversion, HPLC
separation of the product, and resubmission of unreacted
(23) and the monochloroacetate intermediates to the reaction
conditions. This process was repeated three times, giving
(24) in 59% yield. The three halogen substituents and two
thiophenyl groups were then removed in a single step by
using freshly prepared W-2 RaNi[33] in EtOH/THF at 45°C
with sonication, giving the penultimate phenolic acetate
intermediate (25) in 49% yield. Finally, deprotection of the
phenolic acetate was accomplished by using NaHCO3 in
aqueous methanol, which provided analogue (5) with natural
(2S) stereochemistry in 70% yield. Interestingly,
epimerization of the C2 acyloin centre was relatively slow
under these conditions, in striking contrast to our experience
with intermediate (33) in the synthesis of analogue (6) (see
below). Use of KCN–MeOH[34] for the final deprotection of
(25) resulted in rapid decomposition, while use of NH3 or
n-BuNH2/MeOH gave slower rates and correspondingly
lower yields than the NaHCO3 protocol.
63%
Br
O
ClAcO
O
Me
O
PhS
Me
i-PrCO2
O
NH
CCl3
OH
HF/pyridine
I
(20)
AcO
OH
Br
O
(18)
O
THF, pyridine, 0˚C
88%
TBSOTf, 4 Å sieves
CH2Cl2, –15˚C
O
ClAcO
HO
(19)
PhS
W-2 RaNi
EtOH, THF
AcO
OH
Br
O
AcO
OH
Br
O
+
O
O
Br
R
25-45˚C,
sonication
49%
HO
RO
O
O
O
O
RO
O
O
Me
O
PhS
PhS
PhS
Me
i-PrCO2
NH3, MeOH
CH2Cl2, 0˚C
59%
(23) (38%), R = ClAc
(24) R = H
(21) R = ClAc (21%)
(22) R = H (9%)
HO
I
NaHCO3
MeOH, H2O
AcO
OH
Me
O
0˚C
70%
OH OH
Me
O
O
O
Me
HO
Me
O
O
HO
O
O
HO
HO
O
O
O
O
Me
Me
Me
O
Me
O
i-PrCO2
i-PrCO2
(25)
(5)
HO
HO
Scheme 3. Synthesis of aureolic acid analogue (5) with natural
(2S)-acyloin stereochemistry.
It was also of interest to synthesize the (2R)-analogue (6),
in order to determine the role of the stereochemistry of the
acyloin C2 stereocentre on DNA binding and Mg2+ complex
formation. Unfortunately, the ‘C + DE’ coupling strategy
employed for the synthesis of (5) was not successful for the
synthesis of (6) (Scheme 4). Deprotection of the TES ether
(17) provided alcohol (26) in quantitative yield. However, all
attempts to synthesize the protected trisaccharide (30) by
coupling of (26) with the D–E disaccharide
trichloroacetimidate (20) were unsuccessful. The only
products obtained from these experiments were the
chloroacetyl migration product (27) and the diol (28).
Our synthesis of analogue (5) with the natural
(2S)-stereochemistry is summarized in Scheme 3. In the
early stages of this work we used rac-(10) in trimethylsilyl
triflate (TMSOTf) promoted glycosidation reactions with
the C-residue glycosyl trichloroacetimidate (16), thereby
providing an easily separable mixture of diastereomeric
β-glycosides (17) (30%) and (18) (34%).[27–29] It was much
easier to perform the glycosidation reaction using (16) as
the resolving agent than to perform the lipase-mediated
resolution of (10) on a large scale. We also anticipated that
both (17) and (18) could be elaborated to aureolic acid
analogues (see below) by using the glycosidation sequence
employed in our olivomycin A total synthesis.[20] The
stereochemistry at the C2 acyloin centre was determined
by glycosidation of enzymatically resolved (S)-(10) with
(16), which provided (18) in 63% yield. The triethylsilyl
(TES) ether of (18) was removed by treatment with
HF/pyridine in a tetrahydrofuran (THF)/pyridine solvent
mixture, giving alcohol (19) in 88% yield.[30]
Glycosidation of (19) with the D–E disaccharide
(20) TBSOTf
4 Å sieves
AcO
OH
Br
O
AcO
OH
Br
O
AcO
OH
Br
O
+
O
O
O
CH2Cl2
–20 – 0˚C
ClAcO
RO
O
HO
HO
O
HO
ClAcO
O
PhS
PhS
(28)
PhS
(27)
(17) R = TES
(26) R = H
HF/pyridine, THF,
pyridine, 0˚C, 100%
only products observed
Scheme 4. Attempted glycosidation of (26).
trichloroacetimidate
high-performance
(20)[20]
liquid chromatography
provided,
after
(HPLC)
Accordingly, we synthesized the simplified aureolic acid
analogue (6) [with unnatural (2R)-stereochemistry] in the
manner summarized in Scheme 5. Glycosidation of aglycone
(R)-(10) using the C–D–E trisaccharide trichloroacetimidate
separation, trisaccharide (23) in 38% yield, the
chloroacetyl migration product (21) (21%), and diol (22)
(9%). Optimal conditions for the glycosidation reaction

116
W. R. Roush, N. A. Powell and R. A. James
(R)-(10)
OH
Br
Br
ClAc
t-BuNH2
O
O
O
O
ClAcO
MeOH, CH2Cl2
AcO
OH
O
AcO
OH
Br
O
O
O
AcO
OH
Br
O
Me
PhS
PhS
O
Me
i-PrCO2
0˚C
68%
O
TMSOTf, 4 Å MS
CH2Cl2, –78˚C
66%
Br
O
NH
CCl3
ClAc
Br
O
O
O
O
(29)
OH
ClAcO
O
HO
O
O
I
HO
O
Me
O
PhS
PhS
(30)
Me
Me
i-PrCO2
Me
i-PrCO2
PhS
PhS
(31)
O
O
OH
I
OH
I
(Me3Si)3SiH
Et3B, O2
W-2 Raney nickel
EtOH, THF
Pseudomonas
fluorescens lipase
AcO
OH
O
AcO
OH
Me
O
OH OH
Me
HO
O
O
O
O
O
PhCH3, 23˚C
89%
45˚C, sonication
24%
pH 7 buffer, 23˚C
95%
Me
Me
Me
O
Me
O
O
HO
O
O
O
HO
O
HO
O
O
HO
O
HO
O
O
Me
Me
Me
OH
PhS
PhS
(32)
Me
i-PrCO2
Me
i-PrCO2
O
Me
i-PrCO2
O
(33)
(6)
OH
OH
Scheme 5. Synthesis of aureolic acid analogue (6) with unnatural (2R)-acyloin stereochemistry.
(29)* as the glycosyl donor and TMSOTf as the activating
agent provided the trisaccharide conjugate (30) in 66%
yield.[28] None of the corresponding α-glycoside was
detected. The two chloroacetyl protecting groups were
removed selectively in the presence of the phenolic acetate,
giving diol (31) in 68% yield, by using t-BuNH2 in MeOH.†
Use of other amines for this deprotection step resulted in
competitive cleavage of the C8 phenolic acetate and imine
formation (when NH3 was used). Attempted one-step
reduction of the halogen and thiophenyl substituents in (31)
using RaNi in a mixture of THF and EtOH gave (33) in very
low yield (4%). The poor efficiency of this reaction
presumably reflects the lability of the phenolic acetate unit
under these conditions, together with strong complexation of
the fully-deprotected trisaccharide conjugate (6) with the
RaNi catalyst. Better results were obtained when reductive
cleavage of the halogen substituents was decoupled from the
desulfurization step. Thus, reduction of (31) with
tris(trimethylsilyl)silane[35] at ambient temperature using
Et3B and a trace of O2 as the radical initiator[36] provided (32)
in excellent yield (89%). Reduction of a solution of (32) in
EtOH/THF with freshly prepared W-2 RaNi[33] in a
preheated (45°C) sonication bath then provided (33) in 24%
yield (optimized). Deprotection of the remaining C8
phenolic acetate proved somewhat tricky to accomplish
without epimerization of the C2 acyloin stereocentre. Use of
NaHCO3 in aqueous MeOH, conditions that were successful
in the (2S)-epimer series (see above), resulted in substantial
epimerization of the acyloin C2 centre. Since the C8 acetate
had proven labile under the conditions of the enzymatic
resolution conditions employed in the synthesis of (R)-(10),
use of a lipase to hydrolyse the phenolic acetate under very
mild conditions was explored. To our considerable delight,
treatment of acetate (33) with PFL in pH 7 buffer gave the
targeted aureolic acid analogue (2R)-(6) in excellent yield
with no detectable epimerization of C2.‡
Conclusion
Syntheses of aureolic acid analogues (5) and (6) with (2S)-
and (2R)-acyloin stereochemistry, respectively, have been
developed. It is clear from the results presented in
Schemes 3–5 that the one-step glycosidation sequence
leading to trisaccharide conjugate (30) (Scheme 5) is more
efficient than the ‘C + DE’ approach utilized in the synthesis
of (23) (Scheme 3). Nevertheless, sufficient quantities of
(23), and hence also analogue (5), were prepared by the latter
route, so that we did not need to develop a route to (23)
involving the glycosidation of (S)-(10) with (20). The
considerably different behaviour of the intermediates in the
two analogue syntheses is also striking. This is especially
evident by comparison of the conditions required for the
reductive conversion of (24) into (25) in Scheme 3 versus the
conversion of (31) into (33) in Scheme 5, as well as in the
considerably greater sensitivity of (33) to base-catalysed
epimerization (Scheme 5) compared with (25) (Scheme 3).
Finally, the sensitivity of (18) (Scheme 3) and (26)
(Scheme 4) towards chloroacetate migration is also
noteworthy, especially since comparable problems were not
encountered in our olivomycin A synthesis.[20]
The syntheses of (5) and (6) highlight additional
limitations in the use of 2-thiophenyl glycosyl donors for
synthesis of 2-deoxy-β-glycosides, specifically the difficulty
of identifying a protecting group for the C8 phenol that is
fully compatible with the conditions required for reductive
removal of the thiophenyl substituent after completion of the
glycosidation sequence. The 2-deoxy-2-iodoglycosyl donor
*Trisaccharide trichloracetimidate (29) was synthesized by appropriate modifications of our previously published route to the corresponding
bis-C6-O-tosyl C–D–E trisaccharide trichloracetimidate (see supporting information to ref. 27). Complete details will be provided in a full paper
detailing our total synthesis of olivomycin A.
†This reagent combination showed the greatest selectivity for hydrolysis of the chloroacetates and minimization of a number of side reactions, and
was chosen after screening a number of reagents or other amine bases such as thiourea, NH , NH NH , n-BuNH2, and Et3N. See also A. Lubineau,
3
2
2
E. Meyer, P. Place, Carbohydr. Res. 1992, 228, 191.
‡For an earlier example of a lipase-mediated hydrolysis of a phenolic acetate, see ref. 24.

Synthesis of Structurally Simplified Aureolic Acid Analogues
117
1H NMR (CDCl3, 300 MHz) δ 2.08, quintet, J 6.4 Hz, 2H; 2.41, s, 3H;
2.73, dd, J 6.4, 6.4 Hz, 2H; 2.96, dd, J 6.2, 6.2 Hz, 2H; 7.01, m, 2H;
7.52, m, 2H; 14.80, s, 1H. 13C NMR (CDCl3, 75 MHz) δ 21.2, 22.6,
30.0, 38.9, 112.2, 116.7, 117.2, 118.9, 125.4, 130.2, 139.0, 139.5,
148.9, 163.3, 170.3, 205.2.
glycosidation methodology that we recently introduced
promises to solve this problem[32,37] and will be adopted in
our future work on the synthesis of DNA-binding aureolic
acid analogues.
Studies of the DNA binding properties and Mg2+ complex
formation of (5) and (6) are in progress and will be reported
in due course.
8-Acetoxy-2,9-dihydroxy-3,4-dihydro-1(2H)-anthracenone, rac-(10)
A 250 mL round-bottom flask, flame-dried under N2, was charged
with ketone (9) (950 mg, 3.51 mmol) and CH2Cl2 (35 mL). The dark
yellow solution was cooled to –78°C and Et3N (4.0 mL, 28.1 mmol, 8
equiv.) was added, followed by the dropwise addition of TMSOTf
(2.54 mL, 14.1 mmol, 4 equiv.). The resulting fluorescent-yellow
suspension was stirred at –78°C for 1 h, and then poured into 150 mL
of saturated aqueous NaHCO3. The layers were separated, and the
aqueous layer was extracted with CH2Cl2 (× 2). The combined
organic extracts were dried over Na2SO4 and concentrated. The
residue was dissolved in dry CH2Cl2 (25 mL), flushed with N2, and
the solution was cooled to –78°C. Solid NaHCO3 (591 mg, 7.02
mmol, 2 equiv.) was added, followed by recrystallized m-CPBA (1.21
g, 7.02 mmol, 2 equiv.). The resulting slurry was stirred vigorously
while warming to 0°C over 3–4 h. The reaction was quenched by
addition of saturated aqueous NaHCO3 (50 mL), and then saturated
aqueous NaHSO3 (50 mL) was added carefully to avoid foaming. The
biphasic mixture was stirred vigorously for 30 min and then poured
into a separatory funnel containing saturated aqueous NaHCO3 (100
mL) and saturated aqueous Na2HSO3 (100 mL). The aqueous layer
was extracted with CH2Cl2 (× 4). The organic layers were dried over
Na2SO4 and concentrated. The residue was dissolved in MeOH (20
mL) and transferred to a 100 mL flask. The flask was flushed with
N2, and the solution was heated to reflux overnight. The solution was
concentrated, and then the crude product was purified by flash
chromatography (SiO2; 20% EtOAc/hexanes–2% MeOH, then 30%
EtOAc/hexanes–2% MeOH) to give rac-(10) (813 mg, 81%) as a
yellow solid, m.p. 126–131°C (Found: C, 66.6; H, 5.1%; [M + H]+
(CI/NH3), 287.0912. C16H14O5 requires C, 67.1; H, 4.9%; [M + H]+,
287.0919). FT–IR (KBr) 3467, 3060, 3026, 2942, 2875, 2836, 1764,
1629, 1573, 1493, 1459, 1437, 1399, 1375, 1322, 1206, 1174, 1074,
1040, 994, 950, 916, 888, 849, 772 cm–1. 1H NMR (CDCl3, 500
MHz) δ 2.05, ddd, J 12.5, 12.1, 5.9 Hz, 1H; 2.41, s, 3H; 2.51, m, 1H;
3.09, m, 2H; 3.77, s, 1H; 4.41, dd, J 12.8, 5.5 Hz, 1H; 7.05, dd, J 6.8,
1.6 Hz, 1H; 7.09, s, 1H; 7.55, m, 2H; 13.85, s, 1H. 13C NMR (CDCl3,
125 MHz) δ 21.2, 27.5, 30.8, 73.2, 110.4, 117.0, 117.5, 119.4, 125.6,
130.7, 138.4, 139.9, 148.9, 163.2, 170.3, 204.3.
Experimental
General
All reactions were conducted in flame-dried or oven-dried glassware
under an atmosphere of dry nitrogen. All solvents were purified before
use unless otherwise indicated. THF was distilled from sodium
benzophenone ketyl; toluene, Et3N, and pyridine were distilled from
CaH2; CH2Cl2 was distilled from CaH2 or P2O5; MeOH was distilled
from Mg turnings. Crushed 4 Å molecular sieves were activated by
flame-drying under high vacuum immediately prior to use. Solvents
were removed on a rotary evaporator at reduced pressure. Reagents
were purchased and used without further purification.
Analytical thin-layer chromatography (TLC) was performed on
Kieselgel 60 F254 glass plates precoated with a 0.25 mm thickness of
silica gel. The TLC plates were visualized by shortwave and longwave
ultraviolet (UV) light and/or ceric ammonium molybdate stain. Flash
column chromatography was performed according to the method of
Still on Kieselgel 60 (230–400 mesh) silica gel.[38] Preparative
normal-phase HPLC purification was performed using an HPLC
system composed of two Rainin HPXL pumps and a Rainin Dynamax®
UV-C detector connected to either a 10 by 250 mm or a 21 by 250 mm
Dynamax® axial compression column packed with Rainin 60 Å
irregular silica gel. Preparative reverse-phase HPLC purifications were
performed by using
polymer-supported column.
Infrared (IR) spectra were recorded as thin films on NaCl plates or
as KBr pellets using Perkin–Elmer Spectrum 1000 FT–IR
a
10 by 250 mm Dynamax® 60A C18
a
spectrophotometer. UV spectra were recorded on a Shimadzu PC160+
spectrophotometer using quartz solution cells. Melting points are
uncorrected. Optical rotations were measured on a Rudolph Autopol III
polarimeter using a quartz cell with 1 mL capacity and a 10 cm path
length. 1H NMR spectra were measured at 400 MHz on a Varian Inova
400 instrument or at 500 MHz on a Varian Inova 500 instrument using
CDCl3 as solvent. Chemical shifts are reported in δ units using residual
chloroform (7.26 ppm) as an internal reference. 13C NMR spectra were
measured at 100 or 125 MHz using residual chloroform (77.0 ppm) as
an internal reference. High-resolution mass spectra (HRMS) were
measured on a VG 70-250-S Micromass spectrometer. Elemental
analyses were performed by the University of Michigan CHN
Laboratory.
Enzymatic Resolution of rac-(10) with Pseudomonas fluorescens Lipase
A flame-dried 100 mL round-bottom flask was charged with racemic
α-hydroxy ketone (10) (427 mg, 1.49 mmol) and vinyl acetate (40 mL)
freshly distilled from glass. Pseudomonas fluorescens lipase (380 mg,
Fluka) was added, and the cloudy suspension was stirred vigorously at
room temperature. 1H NMR analysis of an aliquot after 5 h showed 50%
conversion. The suspension was filtered through a Celite plug, the plug
rinsed with CH2Cl2, and the filtrate was concentrated under vacuum.
Purification of the crude product by flash chromatography (SiO2; 25%
EtOAc/hexanes–2% MeOH, then 30% EtOAc/hexanes–2% MeOH)
gave acetate (R)-(11) (235 mg, 48%) and alcohol (S)-(10) (200 mg,
47%), [α]D25 –44.9° (c, 1.05 in CHCl3).
(2R)-2,8-Diacetoxy-9-hydroxy-3,4-dihydro-1(2H)-anthracenone
(11), m.p. 145–147°C (Found: C, 65.5; H, 5.0%; M+ (EI), 328.0938.
C18H16O6 requires C, 65.9; H, 4.9%; M+, 328.0947). [α]D25 +154.1° (c,
1.19 in CHCl3). FT–IR (KBr) 3435, 3090, 2949, 2889, 2852, 1758,
1630, 1602, 1572, 1495, 1459, 1437, 1373, 1340, 1303, 1230, 1203,
1178, 1100, 1040, 989, 893, 849, 765, 709, 684 cm–1. 1H NMR (CDCl3,
500 MHz) δ 2.24, s, 3H; 2.27, m, 1H; 2.37, m, 1H; 2.38, s, 3H; 3.16, m,
1H; 5.64, dd, J 12.6, 5.3 Hz, 1H; 7.05, dd, J 6.6, 1.8 Hz, 1H; 7.09, s, 1H;
7.55, m, 2H; 14.19, s, 1H. 13C NMR (CDCl3, 125 MHz) δ 20.8, 21.2,
27.7, 28.6, 73.3, 111.2, 117.1, 117.2, 119.5, 125.6, 130.8, 137.4, 139.7,
149.0, 163.8, 170.2, 170.3, 199.1.
8-Acetoxy-9-hydroxy-3,4-dihydro-1(2H)-anthracenone (9)
A flame-dried 100 mL round-bottom flask was charged with diphenol
ketone (8) (913 mg, 4.00 mmol),[15,16] CH2Cl2 (32 mL) and pyridine
(8 mL), and cooled in an ice bath. Acetyl chloride (0.37 mL, 5.2 mmol,
1.3 equiv.) was added dropwise. After the addition was complete, the
ice bath was removed, and the mixture was stirred at room temperature
for 1 h. The reaction mixture was poured into a separatory funnel
containing saturated aqueous NaHCO3. The layers were separated, and
the aqueous layer was extracted with CH2Cl2 (× 3). The combined
organic layers were dried over Na2SO4 and concentrated under vacuum,
followed by co-evaporation from heptane to remove residual pyridine.
Purification of the crude product by flash chromatography (SiO2; 15%
EtOAc/hexanes–2% MeOH, then 20% EtOAc/hexanes–2% MeOH)
gave (9) (978 mg, 90%) as an orange solid, m.p. 136–138°C (Found: C,
70.5; H, 5.6%; M+ (EI), 270.0892. C16H14O4 requires C, 71.1; H, 5.7%;
M+, 270.0892). FT–IR (KBr) 3447, 3026, 2948, 2875, 1764, 1618,
1459, 1399, 1377, 1356, 1310, 1198, 1167, 1042, 884, 841, 782 cm–1.

118
W. R. Roush, N. A. Powell and R. A. James
(2R)-8-Acetoxy-2,9-dihydroxy-3,4-dihydro-1(2H)-
anthracenone (R)-(10)
dd, J 7.0, 1.5 Hz, 1H; 7.14, tt, J 7.3, 1.1 Hz, 1H; 7.20, t, J 7.3 Hz, 2H;
7.42, d, J 7.3 Hz, 2H; 7.49, dd, J 8.1, 1.5 Hz, 1H; 7.53, t, J 7.5 Hz, 1H;
14.31, s, 1H. 13C NMR (CDCl3, 125 MHz,) δ 5.4 (3C), 6.9 (3C), 21.2,
25.6, 28.0, 30.8, 40.8, 56.7, 72.9, 73.6, 75.5, 76.5, 102.2, 111.3, 116.9,
117.1, 119.2, 125.5, 126.6, 128.7 (2C), 130.3 (2C), 130.5, 135.2, 137.8,
139.6, 149.0, 164.0, 166.3, 170.3, 199.9.
Pseudomonas fluorescens lipase (47 mg, Fluka) was dissolved in
phosphate buffer (25 mL, pH 7, 50 mM). A solution of diacetate
(R)-(11) (53.0 mg, 0.161 mmol) in CH2Cl2 (4 mL) was added to the
buffer–lipase solution. The biphasic mixture was stirred vigorously at
room temperature for 19 h, CH2Cl2 (20 mL) was added and the layers
were separated. The aqueous layer was extracted with CH2Cl2 (× 3).
The combined organic layers were dried over Na2SO4, concentrated
under vacuum, and co-evaporated twice from toluene. The
brownish-yellow solid was dissolved in CH2Cl2 (5 mL) and pyridine (2
mL), and cooled to –15°C in an acetone/ice bath. Ac2O (16 µL, 0.165
mmol, 1.1 equiv.) was added dropwise and the solution was allowed to
warm gradually to 0°C over 7 h. The solution was poured into 1 M
KHSO4 (50 mL) and shaken vigorously. The aqueous layer was
extracted with CH2Cl2 (× 3) and the combined organic layers were
washed with saturated aqueous NaHCO3, dried over Na2SO4, and
concentrated in vacuum. Purification of the crude product by flash
chromatography (SiO2; 25% EtOAc/hexanes–2% MeOH) gave
(R)-(10) (32.4 mg, 70%) as a yellow solid, [α]D25 +48.9° (c, 0.72 in
CHCl3).
Deprotection of (18): Synthesis of Monosaccharide Alcohol (19)
A solution of triethylsilyl ether (18) (272 mg, 0.343 mmol) in THF (10
mL) was flushed with N2 and cooled in an ice bath. Pyridine (1 mL) was
added, followed by the dropwise addition of HF/pyridine complex
(1 mL). The reaction mixture was stirred at 0°C for 45 min. The mixture
was carefully diluted with saturated aqueous NaHCO3, then was poured
into a separatory funnel containing saturated aqueous NaHCO3 and
extracted with EtOAc (× 3). The combined organics were washed with
saturated aqueous NaHCO3 and brine, dried over Na2SO4, concentrated
under vacuum, and co-evaporated from heptane to remove residual
pyridine. Purification of the crude product by flash chromatography
(SiO2; 30% EtOAc/hexanes, then 40% EtOAc/hexanes) gave (19)
(205 mg, 88%) as a yellow oil (Found (FAB): [M + Na]+, 701.0202.
C30H28BrClO9S requires [M + Na]+, 701.0224). [α]D26 +59.5° (c, 0.68
in CHCl3). FT–IR (thin film) 3503, 3058, 2953, 2876, 1760, 1630,
1574, 1458, 1440, 1378, 1334, 1307, 1207, 1173, 1161, 1107, 1046,
1011, 912, 886, 853, 733 cm–1. 1H NMR (CDCl3, 500 MHz) δ 2.26, m,
1H; 2.32, m, 1H; 2.44, s, 3H; 2.88, ddd, J 16.5, 7.7, 4.6 Hz, 2H; 3.01,
m, 2H; 3.07, dd, J 10.6, 8.8 Hz, 1H; 3.43, dd, J 11.4, 7.7 Hz, 1H; 3.51,
dd, J 11.0, 2.7 Hz, 1H; 3.59, dd, J 10.6, 9.0 Hz, 1H; 3.66, ddd, J 7.7, 7.7,
2.6 Hz, 1H; 4.14, s, 2H; 4.56, dd, J 8.1, 4.2 Hz, 1H; 4.94, d, J 8.8 Hz,
1H; 5.02, dd, J 9.3, 9.3 Hz, 1H; 7.05, s, 1H; 7.08, dd, J 7.0, 1.5 Hz, 1H;
7.12, t, J 7.3 Hz, 2H; 7.17, d, J 7.3 Hz, 2H; 7.40, dd, J 8.7, 1.6 Hz, 2H;
7.57, m, 2H; 14.45, s, 1H. 13C NMR (CDCl3, 100 MHz) δ 21.2, 25.8,
29.7, 30.9, 40.6, 56.7, 60.3, 71.1, 72.7, 75.2, 76.4, 101.4, 111.2, 117.0,
119.3, 125.5, 128.0, 128.8 (2C), 130.7, 133.5 (2C), 138.2, 139.7, 148.9,
164.2, 166.5, 170.3, 200.8.
Coupling of (S)-(10) and Trichloroacetimidate (16): Synthesis of
β-Glycoside (18)
A flame-dried 10 mL round-bottom flask was charged with α-hydroxy
ketone (S)-(10) (50.0 mg, 0.175 mmol, 1 equiv.), 4 Å molecular sieves
(44 mg) flame-dried under vacuum, and CH2Cl2 (2.2 mL) distilled from
P2O5. Trichloroacetimidate (16)[20] 164 mg, 0.227 mmol, 1.3 equiv.)
was added, and the cloudy yellow suspension was stirred at ambient
temperature for 20 min. The solution was cooled to –78°C in a dry
ice/acetone bath, then TMSOTf (10 µL, 0.052 mmol, 0.3 equiv.) was
added in a single portion. The suspension was stirred at –78°C for 45
min, and then the reaction was quenched by addition of Et3N (0.2 mL).
The mixture was filtered through a Celite plug, and the filtrate was
washed with saturated aqueous NaHCO3. The aqueous layer was
extracted with CH2Cl2 (× 3). The combined organic layers were dried
over Na2SO4 and concentrated. Purification of the crude product by
flash chromatography (SiO2; 15% EtOAc/hexanes, then 15%
EtOAc/hexanes–2% MeOH), followed by preparative HPLC (25%
EtOAc/hexanes, 21 mm column, 10 mL min–1, λ 290 nm, tR 16.4 min)
gave the β-glycoside (18) (86.7 mg, 63%) as a yellow glassy foam
(Found (FAB): [M + Na]+, 815.0994. C36H42BrClO9SSi requires [M +
Na]+, 815.1088). [α]D25 +107.1° (c, 1.01 in CHCl3). FT–IR (thin film)
3520, 3059, 2956, 2913, 2877, 1766, 1630, 1575, 1461, 1440, 1401,
1380, 1335, 1307, 1238, 1207, 1173, 1161, 1134, 1109, 1065, 1046,
Fully Protected Trisaccharide, (2S)-Epimer (23)
A mixture of alcohol (19) (198 mg, 0.291 mmol, 1 equiv.), D–E
disaccharide trichloroacetimidate (20)[20] (381 mg, 0.426 mmol, 1.5
equiv.), 4 Å molecular sieves (100 mg) activated under vacuum, and
CH2Cl2 (4 mL) distilled from P2O5 was stirred at ambient temperature
for 30 min and then cooled to –15°C in an ice/acetone bath. TBSOTf
(20 µL, 0.087 mmol, 0.3 equiv.) was added in one portion, and the
reaction mixture was allowed to warm gradually to 0°C with stirring
over 2 h. An additional 10 µL of TBSOTf was added, and the mixture
was stirred at 0°C for another 1.5 h. The reaction was quenched by
addition of Et3N (0.5 mL) and the mixture was filtered through a Celite
plug and rinsed with CH2Cl2. The filtrate was washed with saturated
aqueous NaHCO3. The aqueous layer was extracted with CH2Cl2 (× 2).
The combined organic layers were washed with brine, dried over
Na2SO4, and concentrated. Purification of the crude product by flash
1
1014, 912, 884, 854, 823, 802, 739, 689 cm–1. H NMR (CDCl3, 500
MHz) δ 0.64, m, 6H; 0.92, t, J 7.9 Hz, 9H; 2.11, m, 2H; 2.43, s, 3H;
2.71, dd, J 6.0, 6.0 Hz, 2H; 3.21, dd, J 10.3, 8.6 Hz, 1H; 3.41, dd, J 11.0,
7.9 Hz, 1H; 3.46, dd, J 11.0, 3.3 Hz, 1H; 3.68, ddd, J 9.5, 7.7, 3.3 Hz,
1H; 3.77, dd, J 9.9, 8.1 Hz, 1H; 4.13, s, 2H; 4.46, dd, J 6.6, 4.0 Hz, 1H;
4.97, dd, J 9.2, 8.2 Hz, 1H; 5.05, d, J 8.8 Hz, 1H; 6.91, m, 4H; 7.05, dd,
J 7.3, 1.5 Hz, 1H; 7.16, m, 2H; 7.52, dd, J 8.4, 1.3 Hz, 1H; 7.57, t, J 7.7
Hz, 1H; 14.39, s, 1H. 13C NMR (CDCl3, 125 MHz) δ 5.4 (3C), 6.8 (3C),
21.2, 25.2, 29.3, 31.2, 40.8, 56.6, 72.6, 73.1, 75.7, 76.6, 102.7, 111.1,
116.9, 117.1, 119.2, 125.5, 126.3, 128.3 (2C), 130.6, 130.7 (2C), 138.4,
139.7, 149.0, 164.2, 166.4, 170.3, 200.6.
Use of racemic (10) in this glycosidation reaction provided (17) and
(18) in 30 and 34% yields, respectively. Data for (17): (Found (FAB):
[M + Na]+, 815.1066. Calc. for C36H42BrClO9SSi: [M + Na]+,
815.1088). HPLC (25% EtOAc/hexanes, 21 mm column, 10 mL min–1,
tR 19.9 min). [α]D25 –55.7° (c, 1.09 in CHCl3). FT–IR (thin film) 3475,
3351, 3295, 3060, 2956, 2876, 1763, 1631, 1604, 1575, 1461, 1440,
1401, 1380, 1333, 1302, 1239, 1207, 1173, 1160, 1135, 1108, 1066,
1046, 1015, 913, 885, 850, 823, 802, 740, 690 cm–1. 1H NMR (CDCl3,
500 MHz) δ 0.65, m, 6H; 0.93, t, J 7.9 Hz, 9H; 1.96, m, 1H; 2.14, m,
1H; 2.39, s, 3H; 2.79, ddd, J 16.7, 7.3, 4.2 Hz, 1H; 3.05, ddd, J 16.7, 8.1,
4.0 Hz, 1H; 3.31, dd, J 9.9, 8.4 Hz, 1H; 3.36, dd, J 5.5, 1.5 Hz, 1H; 3.65,
m, 1H; 3.78, dd, J 10.1, 8.2 Hz, 1H; 4.12, s, 2H; 4.40, dd, J 7.7, 3.7 Hz,
1H; 4.78, d, J 8.4 Hz, 1H; 4.96, dd, J 8.4, 9.5 Hz, 1H; 6.99, s, 1H; 7.01,
chromatography (SiO2; 25%
EtOAc/hexanes, then 40%
EtOAc/hexanes) followed by preparative HPLC (40% EtOAc/hexanes,
21 mm column, 10 mL min–1, λ 290 nm) gave (23) (155 mg, 38%) as a
yellow glass that contained inseparable impurities. This material was
used directly in the following step without additional purification. In
addition, the acyl transfer product (21) (41 mg, 21%) and diol (22)
(15 mg, 9%) were also isolated. Partial data for impure (23): 1H NMR
(CDCl3, 500 MHz) δ 1.14, d, J 6.2 Hz, 3H; 1.16, d, J 7.0 Hz, 6H; 1.19,
s, 3H; 2.06, m, 1H; 2.14, m, 1H; 2.25, s, 1H; 2.44, s, 3H; 2.57, septet, J
7.0 Hz, 1H; 2.68, m, 2H; 3.17, dd, J 9.8, 9.8 Hz, 1H; 3.24, dd, J 9.3, 9.3
Hz, 1H; 3.36, dd, J 11.5, 7.9 Hz, 1H; 3.43, dd, J 11.4, 7.0 Hz, 1H;
3.62–3.50, m, 5H; 3.78, m, 2H; 4.11, ABq, JAB 15.0 Hz, 1H; 4.15, ABq,
JAB 15.0 Hz, 1H; 4.21, ABq, JAB 15.0 Hz, 1H; 4.27, ABq, JAB 15.0 Hz,
1H; 4.44, dd, J 6.4, 3.8 Hz, 1H; 4.51, s, 1H; 4.88, d, J 8.8 Hz, 1H; 4.91,
dd, J 9.2, 9.2 Hz, 1H; 5.01, dd, J 9.2, 9.2 Hz, 1H; 5.04, d, J 8.4 Hz, 1H;
5.16, d, J 9.2 Hz, 1H; 5.39, s, 1H; 6.87, t, J 7.5 Hz, 2H; 6.93, s, 1H; 6.98,
t, J 7.3 Hz, 1H; 7.07, d, J 7.3 Hz, 1H; 7.13, d, J 7.3 Hz, 2H; 7.18, t, J
7.3 Hz, 1H; 7.30, d, J 7.7 Hz, 2H; 7.37, d, J 7.7 H2, 2H; 7.53, d, J 8.1 Hz,
1H; 7.59, t, J 7.8 Hz, 1H; 14.39, s, 1H. 13C NMR (CDCl3, 125 MHz) δ

Synthesis of Structurally Simplified Aureolic Acid Analogues
119
17.4, 18.8, 18.9 (2C), 20.6, 21.3, 25.1, 29.3, 30.8, 31.0, 34.1 (2C), 40.9,
41.1, 46.1, 54.1, 54.9, 68.6, 70.8, 72.2, 72.5, 73.3, 74.7, 75.6, 76.1,
76.9, 82.1, 102.1, 103.1, 105.2, 111.1, 117.0, 119.2, 125.5, 126.2,
126.9, 128.4 (2C), 128.5 (2C), 129.0 (2C), 130.7, 131.6 (2C), 133.4,
135.2, 138.3, 139.8, 149.0, 164.3, 166.3, 166.4, 170.3, 177.1, 200.5.
J 11.9, 8.4, 5.3 Hz, 1H; 3.55, ddd, J 11.9, 8.4, 5.3 Hz, 1H; 3.99, dq, J
9.5, 6.2 Hz, 1H; 4.07, s, 1H; 4.45, br s, 1H; 4.55, d, J 10.6 Hz, 1H; 4.57,
dd, J 10.6, 3.3 Hz, 1H; 4.59, d, J 9.5 Hz, 1H; 4.94, dd, J 9.9, 1.8 Hz, 1H;
5.01, dd, J 4.2, 2.0 Hz, 1H; 7.04, dd, J 6.6, 2.2 Hz, 1H; 7.08, s, 1H; 7.54,
m, 2H; 14.37, s, 1H. 13C NMR (CDCl3, 125 MHz) δ 17.7, 17.8, 17.9,
18.9, 19.0, 21.2, 22.9, 27.2, 30.1, 34.2, 37.1, 37.3, 43.8, 66.6, 70.6,
72.1, 72.2, 75.0, 75.2, 79.4, 80.9, 82.3, 97.3, 99.5, 99.6, 111.3, 117.1
(2C), 119.3, 125.6, 103.6, 138.1, 139.8, 148.9, 163.8, 170.3, 177.5,
203.1.
Deprotection of Trisaccharide (23): Synthesis of Trisaccharide Triol
(24)
A solution of slightly impure trisaccharide (23) (142 mg, 0.114 mmol)
in CH2Cl2 (6 mL) was cooled in an ice bath. A methanolic NH3 solution
(6 mL, 2 M) was added slowly. The reaction mixture was stirred until
homogeneous, and then was allowed to stand without stirring at 0°C for
4 h until the reaction was about 50% complete by TLC analysis. The
light-red solution was poured into 1 M KHSO4 (75 mL) and extracted
with CH2Cl2 (× 3). The combined organic layers were washed with
brine, dried over Na2SO4, and concentrated. Purification of the crude
product by preparative HPLC (40% EtOAc/hexanes, 21 mm column, 10
mL min–1, λ 290 nm, tR 16.35 min) gave diol (24) (47.8 mg, 38%) and
a mixture of (23) and monochloroacetates (68.7 mg). The latter mixture
was resubmitted to the reaction conditions to give a combined yield of
triol (24) (74.7 mg, 59%) as a yellow glass (Found (FAB): [M + Na]+,
1283.0. C51H57Br2IO15S2 requires [M + Na]+, 1283.8). [α]D25 +111.1°
(c, 0.46 in CHCl3). FT–IR (thin film) 3488, 3058, 2976, 2938, 2877,
1739, 1626, 1576, 1472, 1457, 1439, 1400, 1380, 1359, 1335, 1258,
1205, 1173, 1160, 1085, 1044, 912, 884, 853, 814, 735 cm–1. 1H NMR
(CDCl3, 500 MHz) δ 1.18, d, J 7.0 Hz, 3H; 1.19, d, J 7.0 Hz, 3H; 1.30,
s, 3H; 1.31, d, J 5.1 Hz, 3H; 2.13, m, 3H; 2.22, s, 1H; 2.42, s, 3H; 2.60,
septet, J 7.0 Hz, 1H; 2.70, m, 2H; 3.15, dd, J 10.6, 9.2 Hz, 1H; 3.20, dd,
J 10.6, 8.8 Hz, 1H; 3.38, dd, J 11.0, 7.7 Hz, 1H; 3.49, m, 4H; 3.58, ddd,
J 10.8, 7.6, 7.6 Hz, 2H; 3.65, dd, J 11.4, 4.8 Hz, 1H; 3.77, dd, J 11.2,
2.4 Hz, 1H; 3.83, dd, J 12.3, 1.8 Hz, 1H; 3.85, s, 1H; 4.04, s, 1H; 4.07,
dd, J 6.8, 6.8 Hz, 1H; 4.27, d, J 3.3 Hz, 1H; 4.46, dd, J 6.3, 4.0 Hz, 1H;
4.92, d, J 8.8 Hz, 1H; 4.95, d, J 7.3 Hz, 1H; 4.99, d, J 8.8 Hz, 1H; 5.35,
d, J 3.7 Hz, 1H; 6.77, t, J 7.7 Hz, 2H; 6.87, t, J 7.5 Hz, 1H; 6.92, s, 1H;
7.05, dd, J 7.3, 1.1 Hz, 1H; 7.11, dd, J 7.7, 1.5 Hz, 2H; 7.18, d, J 7.0 Hz,
1H; 7.22, t, J 7.3 Hz, 2H; 7.32, dd, J 7.3, 1.5 Hz, 2H; 7.51, dd, J 8.4,
1.1 Hz, 1H; 7.56, t, J 7.7 Hz, 1H; 14.40, s, 1H. 13C NMR (CDCl3, 125
MHz) δ 17.4, 18.8, 18.9, 21.3, 23.0, 29.4, 32.1, 32.8, 34.0 (2C), 43.9,
54.3, 54.6, 70.1, 71.6, 71.7, 72.2, 73.7, 74.5, 75.1, 75.8, 82.0, 85.4,
102.8, 102.9, 103.5, 111.1, 116.9, 117.1, 119.2, 125.5, 126.4, 126.6,
128.1 (2C), 128.9 (2C), 130.1 (2C), 130.6, 131.2 (2C), 134.3, 135.3,
138.4, 139.7, 149.0, 164.2, 170.3, 176.6, 200.6.
Aureolic Acid Analogue (5), (2S)-Epimer
A solution of phenolic acetate (25) (2.1 mg, 0.0027 mmol) in MeOH
(0.5 mL) was prepared in a 1 dram screw-capped vial. A solution of
saturated NaHCO3 (0.1 mL) in deionized H2O (0.4 mL) was added
dropwise with stirring. The vial was flushed with N2 and stirred at
ambient temperature for 2 h. The solution was poured into a separatory
funnel containing H2O (10 mL), and extracted with CH2Cl2 (× 3). The
combined organic phases were dried over Na2SO4 and concentrated.
Purification of the crude product by preparative HPLC (80%
EtOAc/hexanes, 10 mm column, 5 mL min–1, λ 265 nm, tR 7.5 min)
gave (5) (1.4 mg, 71%) as a yellow glass (Found (FAB): [M + Na]+,
741.3125. C37H50O14 requires [M + Na]+, 741.3098). [α]D25 –165.5° (c,
0.20 in CHCl3). FT–IR (thin film) 3402, 2975, 2935, 2876, 1734, 1635,
1577, 1450, 1419, 1386, 1345, 1306, 1248, 1161, 1127, 1069, 1022,
907, 852 cm–1. 1H NMR (CDCl3, 500 MHz) δ 1.21, d, J 6.8 Hz, 3H;
1.22, d, J 7.1 Hz, 3H; 1.23, d, J 6.4 Hz, 3H; 1.35, s, 3H; 1.38, d, J 6.1
Hz, 3H; 2.00, dd, J 14.0, 4.3 Hz, 1H; 1.39, d, J 6.1 Hz, 3H; 1.69, ddd, J
12.3, 12.3, 10.0 Hz, 1H; 1.73, ddd, J 12.3, 12.3, 9.9 Hz, 1H; 2.05, dd, J
13.9, 2.0 Hz, 1H; 2.22, m, 1H; 2.26, ddd, J 12.9, 5.1, 2.0 Hz, 1H; 2.36,
ddd, J 12.7, 5.4, 2.0 Hz, 1H; 2.39, s, 1H; 2.41, dq, J 13.2, 4.8 Hz, 1H;
2.64, septet, J 7.1 Hz, 1H; 3.03, ddd, J 15.6, 11.0, 3.8 Hz, 1H;
3.16–3.03, m, 3H; 3.30, dq, J 9.0, 6.1 Hz, 1H; 3.37, dq, J 9.0, 6.2 Hz,
1H; 3.48, ddd, J 11.7, 8.3, 5.3 Hz, 1H; 3.57, ddd, J 11.7, 8.3, 5.3 Hz, 1H;
3.99, dq, J 9.5, 6.2 Hz, 1H; 4.06, s, 1H; 4.48, br s, 1H; 4.56, dd, J 10.0,
2.0 Hz, 1H; 4.59, dd, J 11.1, 4.5 Hz, 1H; 4.60, d, J 9.3 Hz, 1H; 4.96, dd,
J 9.9, 1.8 Hz, 1H; 5.01, dd, J 4.2, 2.0 Hz, 1H; 6.85, d, J 7.8 Hz, 1H; 7.00,
s, 1H; 7.13, d, J 8.1 Hz, 1H; 7.49, t, J 7.9 Hz, 1H; 9.60, s, 1H; 15.57, s,
1H. 13C NMR (CDCl3, 125 MHz) δ 17.8, 17.9, 18.0, 18.9, 19.0, 22.9,
27.2, 30.4, 34.2, 37.1, 37.4, 43.9, 66.6, 70.6, 72.1, 72.2, 75.0, 75.3,
76.6, 79.5, 80.9, 82.2, 97.3, 99.6, 99.8, 109.5, 110.9, 112.5, 117.4,
118.2, 132.9, 136.9, 139.5, 157.9, 165.8, 177.5, 202.9.
Glycosidation of (R)-(10) with C–D–E Trisaccharide
RaNi Reduction of (24): Synthesis of Phenolic Acetate (25)
Trichloroacetimidate (29): Synthesis of Trisaccharide (30)
A flame-dried 25 mL round-bottom flask was charged with (24) (52.8
mg, 0.0419 mmol), dry THF (8 mL), and 120 pipette drops of freshly
prepared W-2 Raney nickel suspension in EtOH.[33] The suspension was
sonicated for 3 h, while the bath temperature was kept below 45°C. An
additional 90 drops of RaNi suspension were added every 60 min, until
TLC analysis showed 100% conversion of (24). The greenish-black
suspension was diluted with MeOH and filtered through a Celite plug
to remove the nickel metal. The filter pad was rinsed with MeOH and
the combined filtrate was concentrated. The residue was passed through
a SiO2 plug, with 75% EtOAc/hexanes–2% MeOH as eluent, and was
then purified by preparative HPLC (80% EtOAc/hexanes, 21 mm
column, 10 mL min–1, λ 290 nm, tR 17.2 min) to give (25) (15.6 mg,
49%) as a yellow glass (Found (FAB): [M + Na]+, 783.3279. C39H52O15
requires [M + Na]+, 783.3204). [α]D25 –118.6° (c, 0.36 in CHCl3).
FT–IR (thin film) 3430, 2975, 2936, 2879, 1765, 1735, 1630, 1576,
1457, 1367, 1333, 1204, 1162, 1127, 1069, 1022, 907, 852, 755 cm–1.
1H NMR (CDCl3, 500 MHz) δ 1.21, d, J 7.0 Hz, 3H; 1.22, d, J 7.0 Hz,
3H; 1.23, d, J 7.3 Hz, 3H; 1.35, s, 3H; 1.38, d, J 6.2 Hz, 3H; 1.39, d, J
6.2 Hz, 3H; 1.68, ddd, J 12.1, 12.1, 10.3 Hz, 1H; 1.72, ddd, J 12.1, 12.1,
9.9 Hz, 1H; 2.00, dd, J 13.9, 4.4 Hz, 1H; 2.04, s, 1H; 2.06, dd, J 13.9,
1.8 Hz, 1H; 2.27–2.00, m, 2H; 2.42–2.34, m, 2H; 2.39, s, 3H; 2.64,
septet, J 7.0 Hz, 1H; 3.16–3.03, m, 3H; 3.18, ddd, J 16.5, 4.6, 4.6 Hz,
1H; 3.28, dq, J 9.2, 6.2 Hz, 1H; 3.37, dq, J 9.2, 6.2 Hz, 1H; 3.48, ddd,
A flame-dried 10 mL round-bottom flask was charged with acyloin
(R)-(10) (20.0 mg, 0.067 mmol, 1.5 equiv.) [pre-dried by
co-evaporation from PhH (× 2)] and flushed with N2. Trisaccharide
trichloroacetimidate (29)* (65.6 mg, 0.051 mmol, 1 equiv.), 4 Å
molecular sieves (30 mg), and CH2Cl2 (1.3 mL) (distilled from P2O5)
were added, and the resulting yellow suspension was stirred at ambient
temperature for 15 min. The mixture was cooled to –78°C in a dry
ice/acetone bath, and then TMSOTf (4 µL, 0.022 mmol, 0.4 equiv.) was
added in a single portion. The reaction mixture was stirred at –78°C for
45 min, quenched with Et3N, and filtered through a Celite plug which
was washed with CH2Cl2. The filtrate was extracted with saturated
aqueous NaHCO3, and the aqueous layer was extracted with CH2Cl2
(× 2). The combined organic layers were dried over Na2SO4 and
concentrated. Purification of the crude product by flash
chromatography (SiO2, 30% EtOAc/hexanes–2% MeOH) and then
preparative HPLC (40% EtOAc/hexanes, 21 mm column, 10 mL min–1,
λ 290 nm, tR 17.1 min) gave trisaccharide (30) (47.7 mg, 66%) as a
yellow glass (Found (FAB): [M + Na]+, 1437.0. C55H59Br2Cl2IO17S2
requires [M + Na]+, 1437.1). [α] 25 –71.5° (c, 0.41 in CHCl3). FT–IR
D
(thin film) 3468, 3453, 3060, 3020, 2974, 2944, 2878, 1763, 1733,
1629, 1604, 1576, 1458, 1439, 1400, 1358, 1334, 1315, 1259, 1204,
1161, 1127, 1046, 1024, 824, 745 cm–1. 1H NMR (CDCl3, 500 MHz) δ
1.14, d, J 7.0 Hz, 3H; 1.15, d, J 7.0 Hz, 3H; 1.16, d, J 7.0 Hz, 3H; 1.19,
*See footnote * on p. 116.

120
W. R. Roush, N. A. Powell and R. A. James
s, 3H; 1.89, m, 1H; 2.13, m, 1H; 2.24, s, 1H; 2.39, s, 3H; 2.56, septet, J
7.0 Hz, 1H; 2.78, ddd, J 16.7, 7.9, 4.2 Hz, 1H; 3.00, ddd, J 16.5, 7.9,
4.0 Hz, 1H; 3.14, dd, J 10.8, 9.0 Hz, 1H; 3.34, dd, J 7.3, 2.9 Hz, 1H;
3.36, dd, J 8.1, 3.5 Hz, 1H; 3.41, dd, J 11.0, 2.9 Hz, 1H; 3.48, dd, J 11.4,
2.6 Hz, 1H; 3.55, ddd, J 7.7, 7.7, 2.6 Hz, 1H; 3.57, dd, J 11.0, 8.8 Hz,
1H; 3.74, ddd, J 7.3, 7.3, 2.9 Hz, 1H; 3.79, dq, J 9.2, 6.2 Hz, 1H; 3.93,
dd, J 9.0, 9.0 Hz, 1H; 4.10, ABq, JAB 15.0 Hz, 1H; 4.15, ABq, JAB
14.7 Hz, 1H; 4.18, ABq, JAB 14.7 Hz, 1H; 4.23, AB, JAB 15.0 Hz, 1H;
4.37, dd, J 8.1, 4.0 Hz, 1H; 4.51, d, J 1.8 Hz, 1H; 4.77, d, J 8.1 Hz, 1H;
4.88, d, J 9.2 Hz, 1H; 4.89, dd, J 9.7, 8.6 Hz, 1H; 5.01, dd, J 9.7, 8.2 Hz,
1H; 5.04, d, J 8.8 Hz, 1H; 5.40, d, J 1.5 Hz, 1H; 6.99, s, 1H; 7.02, dd, J
7.1, 1.3 Hz, 1H; 7.09, tt, J 7.1, 1.1 Hz, 1H; 7.19, m, 5H; 7.25, m, 2H;
7.42, m, 2H; 7.50, dd, J 8.4, 1.3 Hz, 1H; 7.54, t, J 7.7 Hz, 1H; 14.28, s,
1H. 13C NMR (CDCl3, 100 MHz) δ 17.4, 18.8, 18.9, 20.7, 21.2, 25.7,
28.1, 30.7, 30.8, 34.1, 40.8, 41.0, 46.0, 54.3, 54.9, 60.4, 68.6, 70.8,
72.7, 72.8, 73.3, 74.8, 76.2, 77.3, 78.4, 82.0, 101.5, 103.1, 105.2, 111.3,
116.9, 117.1, 119.2, 125.5, 126.4, 127.4, 128.6, 128.9 (2C), 129.0 (2C),
130.5, 131.6 (2C), 133.7, 134.8, 137.7, 139.6, 149.0, 164.0, 166.2,
166.4, 170.3, 199.9.
1631, 1574, 1440, 1400, 1380, 1359, 1331, 1204, 1158, 1117, 1071,
1026, 1000, 747 cm–1. 1H NMR (CDCl3, 500 MHz) δ 1.18, d, J 7.3 Hz,
3H; 1.19, d, J 7.3 Hz, 3H; 1.20, s, 3H; 1.23, d, J 6.6 Hz, 3H; 1.30, d, J
5.9 Hz, 3H; 1.38, d, J 6.2 Hz, 3H; 1.96, dd, J 13.9, 4.4 Hz, 1H; 2.01, m,
1H; 2.14, dd, J 13.6, 2.2 Hz, 1H; 2.16, m, 1H; 2.29, s, 1H; 2.38, s, 3H;
2.61, septet, J 7.0 Hz, 1H; 2.79, ddd, J 16.7, 7.5, 4.4 Hz, 1H; 3.05, m,
1H; 3.07, dd, J 9.9, 9.9 Hz, 1H; 3.30–3.18, m, 4H; 3.33, dq, J 9.3, 6.0
Hz, 1H; 3.43, dq, J 9.2, 6.0 Hz, 1H; 3.46, dd, J 10.8, 8.2 Hz, 1H; 3.99,
dq, J 9.2, 6.2 Hz, 1H; 4.23, s, 1H; 4.27, s, 1H; 4.37, dd, J 8.1, 3.7 Hz,
1H; 4.59, d, J 8.8 Hz, 1H; 4.64, d, J 9.2 Hz, 1H; 4.76, d, J 8.8 Hz, 1H;
4.98, dd, J 3.7, 2.0 Hz, 1H; 6.97, s, 1H; 7.01, d, J 7.0 Hz, 1H; 7.05, m,
2H; 7.12, m, 3H; 7.18, m, 2H; 7.41, d, J 6.6 Hz, 1H; 7.48, d, J 7.3 Hz,
1H; 7.52, t, J 7.7 Hz, 1H; 14.30, s, 1H. 13C NMR (CDCl3, 125 MHz) δ
17.5, 17.6, 17.8, 18.8, 18.9, 21.2, 22.8, 25.7, 28.1, 29.7, 34.2, 42.9,
54.6, 55.8, 67.3, 70.5, 71.6, 71.7, 74.7, 75.3, 77.2, 78.7, 78.9, 83.2,
87.4, 100.6, 103.0, 103.6, 111.4, 116.9, 117.1, 119.1, 125.5, 126.4,
128.3 (2C), 128.6 (2C), 130.3 (2C), 130.5 (2C), 135.5, 136.0, 137.9,
139.6, 148.9, 163.8, 170.3, 177.3, 200.5.
RaNi Reduction of (32): Synthesis of Phenolic Acetate (33)
Trisaccharide Diol (31)
A flame-dried 50 mL round-bottom flask was charged with bis(phenyl
sulfide) (32) (32.2 mg, 0.033 mmol) and dry THF (16 mL). About 100
pipette drops of a freshly prepared W-2 Raney nickel suspension in
EtOH[33] were added. The resulting greenish-black suspension was
sonicated at 40°C in a preheated bath for 30 min, with the bath
temperature being maintained between 40–45°C. An additional 60
drops of Raney nickel suspension were added and the mixture was
sonicated at 45°C for another 30 min. After being cooled to ambient
temperature, the suspension was diluted with 3% HOAc/MeOH
(20 mL), stirred vigorously, and filtered through a Celite plug, which
was rinsed twice with 3% HOAc/MeOH (20 mL). The combined
filtrates were concentrated to 1/4 volume, diluted with EtOAc (30 mL),
and washed twice with H2O. The combined aqueous layers were
back-extracted with EtOAc. The combined organic layers were washed
with saturated aqueous NaHCO3, dried over Na2SO4, and concentrated.
The resulting greenish-black residue was passed through a SiO2 plug,
with 80% EtOAc/hexanes–2% MeOH as eluent. Purification of the
crude product by preparative HPLC (80% EtOAc/hexanes, 10 mm
column, 5 mL min–1, λ 290 nm, tR 12.0 min) gave (33) (5.9 mg, 24%)
as a yellow glass (Found (FAB): [M + Na]+, 783.3237. C39H52O15
requires [M + Na]+, 783.3204). [α]D27 –97.7° (c, 0.22 in CHCl3). FT–IR
(thin film) 3436, 3058, 2976, 2934, 2879, 1766, 1738, 1631, 1574,
1440, 1400, 1380, 1359, 1331, 1204, 1158, 1117, 1071, 1026, 1000,
747 cm–1. 1H NMR (CDCl3, 500 MHz) δ 1.18, d, J 7.3 Hz, 3H; 1.19, d,
J 7.3 Hz, 3H; 1.20, s, 3H; 1.23, d, J 6.6 Hz, 3H; 1.30, d, J 5.9 Hz, 3H;
1.38, d, J 6.2 Hz, 3H; 1.96, dd, J 13.9, 4.4 Hz, 1H; 2.01, m, 1H; 2.14,
dd, J 13.6, 2.2 Hz, 1H; 2.16, m, 1H; 2.29, s, 1H; 2.38, s, 3H; 2.61, septet,
J 7.0 Hz, 1H; 2.79, ddd, J 16.7, 7.5, 4.4 Hz, 1H; 3.05, m, 1H; 3.07, dd,
J 9.9, 9.9 Hz, 1H; 3.30–3.18, m, 4H; 3.33, dq, J 9.3, 6.0 Hz, 1H; 3.43,
dq, J 9.2, 6.0 Hz, 1H; 3.46, dd, J 10.8, 8.2 Hz, 1H; 3.99, dq, J 9.2,
6.2 Hz, 1H; 4.23, s, 1H; 4.27, s, 1H; 4.37, dd, J 8.1, 3.7 Hz, 1H; 4.59, d,
J 8.8 Hz, 1H; 4.64, d, J 9.2 Hz, 1H; 4.76, d, J 8.8 Hz, 1H; 4.98, dd, J 3.7,
2.0 Hz, 1H; 6.97, s, 1H; 7.01, d, J 7.0 Hz, 1H; 7.05, m, 2H; 7.12, m, 3H;
7.18, m, 2H; 7.41, d, J 6.6 Hz, 1H; 7.48, d, J 7.3 Hz, 1H; 7.52, t, J
7.7 Hz, 1H; 14.30, s, 1H. 13C NMR (CDCl3, 125 MHz) δ 17.5, 17.6,
17.8, 18.8, 18.9, 21.2, 22.8, 25.7, 28.1, 29.7, 34.2, 42.9, 54.6, 55.8,
67.3, 70.5, 71.6, 71.7, 74.7, 75.3, 77.2, 78.7, 78.9, 83.2, 87.4, 100.6,
103.0, 103.6, 111.4, 116.9, 117.1, 119.1, 125.5, 126.4, 128.3 (2C),
128.6 (2C), 130.3 (2C), 130.5 (2C), 135.5, 136.0, 137.9, 139.6, 148.9,
163.8, 170.3, 177.3, 200.5.
A mixture of trisaccharide (30) (392 mg, 0.278 mmol), dry CH2Cl2
(3 mL), and dry MeOH (3 mL) was cooled in an ice bath, and then
t-BuNH2 (295 µL, 2.78 mmol, 10 equiv.) was added dropwise with
stirring. The resulting dark red solution was allowed to stand at 0°C for
5 h, then was poured into 1 M KHSO4 (25 mL), and was extracted with
CH2Cl2 (× 4). The combined organics were washed with brine, dried
over Na2SO4, and concentrated. Purification of the crude product by
flash chromatography (SiO2, 30% EtOAc/hexanes–2% MeOH) gave
(31) (210 mg) as a yellow solid and a mixture of unreacted (30) and
intermediate monochloroacetates, which was resubmitted to the
reaction conditions for another 6 h. Workup and purification as
described above gave (31) (226 mg, 65%) as a yellow solid (Found
(FAB): [M + Na]+, 1283.5. C51H57Br2IO15S2 requires [M + Na]+,
1283.8). [α]D27 –31.5° (c, 0.91 in CHCl3). FT–IR (thin film) 3480,
3058, 2976, 2936, 2879, 1737, 1630, 1603, 1574, 1439, 1400, 1380,
1358, 1332, 1258, 1205, 1172, 1159, 1084, 1042, 911, 814, 737, 690
1
cm–1. H NMR (CDCl3, 500 MHz) δ 1.18, d, J 7.0 Hz, 3H; 1.19, d, J
7.0 Hz, 3H; 1.33, d, J 6.6 Hz, 3H; 1.33, s, 3H; 2.01, m, 1H; 2.21, m, 1H;
2.24, s, 1H; 2.39, s, 3H; 2.60, septet, J 7.0 Hz, 1H; 2.82, ddd, J 14.7, 8.4,
4.9 Hz, 1H; 3.05, ddd, J 16.9, 8.1, 4.0 Hz, 1H; 3.18, dd, J 11.0, 8.8 Hz,
1H; 3.27, dd, J 10.6, 8.8 Hz, 1H; 3.50–3.38, m, 6H; 3.58, dd, J 10.4,
7.5 Hz, 1H; 3.64, dd, J 11.0, 4.4 Hz, 1H; 3.78, m, 2H; 3.84, s, 1H; 4.05,
s, 1H; 4.08, dd, J 6.8, 6.8 Hz, 1H; 4.31, d, J 3.3 Hz, 1H; 4.46, dd, J 8.4,
3.7 Hz, 1H; 4.71, d, J 8.8 Hz, 1H; 4.93, d, J 8.8 Hz, 1H; 4.96, d, J 7.0 Hz,
1H; 5.38, d, J 3.3 Hz, 1H; 6.99, s, 1H; 7.02, dd, J 7.0, 1.5 Hz, 1H; 7.06,
m, 3H; 7.26–7.14, m, 5H; 7.39, m, 2H; 7.49, dd, J 8.1, 1.1 Hz, 1H; 7.53,
t, J 7.7 Hz, 1H; 14.32, s, 1H. 13C NMR (CDCl3, 125 MHz) δ 17.4, 18.8,
18.9, 21.2, 23.0, 25.9, 27.9, 32.0, 32.2, 34.1, 43.9, 54.4, 54.7, 70.2,
71.6, 71.8, 72.0, 73.8, 75.1, 75.2, 78.3, 82.6, 85.5, 102.3, 103.1, 103.7,
111.3, 116.8, 117.1, 119.2, 125.5, 126.6, 128.5 (2C), 128.9 (2C), 130.2
(2C), 130.4, 130.6 (2C), 134.8, 135.2, 137.8, 139.6, 149.0, 163.9,
170.3, 176.6, 200.0.
Tris(trimethylsilyl)silane Reduction of (31): Synthesis of Trisaccharide
(32)
A solution of the diol (31) (51.0 mg, 0.040 mmol, 1 equiv.) in dry
toluene (8 mL) was treated with tris(trimethylsilyl)silane (250 µL,
0.809 mmol, 20 equiv.) and Et3B (120 µL, 0.120 mmol, 1 M in hexane).
The N2 purge was removed and 50 µL of air was injected directly into
the yellow solution. The mixture was stirred at room temperature for 1 h
and then diluted with EtOAc and washed with saturated aqueous
NaHCO3. The organic layer was dried over Na2SO4 and concentrated
under vacuum, keeping the rotary evaporator bath temperature below
30°C. Purification of the crude product by flash chromatography (SiO2;
40% EtOAc/hexanes, then 40% EtOAc/hexanes–2% MeOH) gave (32)
(35.2 mg, 89%) as a yellow foam (Found (FAB): [M + Na]+, 999.3290.
C51H60O15S2 requires [M + Na]+, 999.3271). [α]D27 –46.6° (c, 0.70 in
CHCl3). FT–IR (thin film) 3436, 3058, 2976, 2934, 2879, 1766, 1738,
Aureolic Acid Analogue (6), (2R)-Epimer
Phenolic acetate (33) (9.6 mg, 0.0126 mmol) was dissolved in CH2Cl2
(300 µL) in a 10 mL pear-shaped flask under a N2 atmosphere. In a
separate vial, Pseudomonas fluorescens lipase (11.9 mg) (PFL, Fluka)
was dissolved in phosphate buffer (3.7 mL, pH 7, 50 mM). The
PFL–buffer solution was added to the solution of (33) and the biphasic
mixture was stirred vigorously at ambient temperature for 14 h. The
mixture was diluted with deionized H2O and extracted with CH2Cl2

121
W. R. Roush, N. A. Powell and R. A. James
(× 4). The combined organic phases were washed with H2O and brine,
dried over Na2SO4, and concentrated. The crude product was purified
by reverse-phase preparative HPLC using a gradient program (0–1 min
35% H2O with 0.1% AcOH and 65% 3:1 CH3CN/H2O with 0.1%
AcOH, 1–30 min linear gradient to 100% 3:1 CH3CN/H2O with 0.1%
AcOH, 5 mL min–1, tR 22.1 min). The CH3CN was removed under
vacuum, and the aqueous phase was extracted with CH2Cl2 (× 4). The
combined organic layers were washed with H2O and brine, dried over
Na2SO4, concentrated, and dried by co-evaporation twice from benzene
to give analogue (6) (8.5 mg, 95%) as a dark yellow glass (Found
(FAB): [M+Na]+, 741.3091. C37H50O14 requires [M+Na]+, 741.3098).
[α]D25 –46.7° (c, 0.85 in CHCl3). FT–IR (thin film) 3412, 3065, 2975,
2934, 2879, 2245, 1732, 1634, 1604, 1582, 1450, 1416, 1385, 1345,
1310, 1250, 1162, 1127, 1069, 1022, 908, 733 cm–1. 1H NMR (CDCl3,
500 MHz) δ 1.20, d, J 7.1 Hz, 3H; 1.21, d, J 6.8 Hz, 3H; 1.23, d, J
5.9 Hz, 3H; 1.33, d, J 6.1 Hz, 3H; 1.35, s, 3H; 1.38, d, J 6.1 Hz, 3H;
1.69, ddd, J 12.0, 10.3, 10.3 Hz, 1H; 1.83, ddd, J 12.2, 10.0, 10.0 Hz,
1H; 2.00, dd, J 13.8, 4.3 Hz, 1H; 2.05, dd, J 13.8, 2.1 Hz, 1H; 2.28–2.17,
m, 3H; 2.38, m, 1H; 2.42, br s, 1H; 2.64, septet, J 7.1 Hz, 1H; 2.98, ddd,
J 10.6, 4.3, 4.3 Hz, 1H; 3.11, t, J 8.5 Hz, 1H; 3.14, t, J 8.8 Hz, 1H; 3.19,
ddd, J 16.6, 5.1, 5.1 Hz, 1H; 3.26, dq, J 9.3, 6.1 Hz, 1H; 3.35, dq, J 9.2,
6.1 Hz, 1H; 3.48, ddd, J 11.7, 8.2, 5.0 Hz, 1H; 3.52, ddd, J 11.8, 8.4,
5.3 Hz, 1H; 3.99, dq, J 9.5, 6.2 Hz, 1H; 4.05, d, J 1.2 Hz, 1H; 4.46, s,
1H; 4.54, dd, J 9.9, 1.8 Hz, 1H; 4.59, d, J 9.5 Hz, 1H; 4.60, dd, J 10.0,
4.2 Hz, 1H; 4.72, dd, J 9.8, 2.0 Hz, 1H; 5.00, dd, J 4.2, 2.0 Hz, 1H; 6.84,
d, J 7.6 Hz, 1H; 6.99, s, 1H; 7.12, d, J 7.6 Hz, 1H; 7.48, t, J 7.9 Hz, 1H;
9.63, s, 1H; 15.62, br s, 1H. 13C NMR (CDCl3, 125 MHz) δ 17.7, 17.8,
17.9, 18.9, 19.0, 23.0, 26.7, 28.9, 34.2, 37.1, 37.4, 43.9, 66.6, 70.6,
72.1, 72.3, 74.8, 75.2, 79.5, 80.8, 82.3, 94.8, 97.1, 97.2, 99.6, 109.8,
110.9, 112.5, 117.3, 118.1, 132.8, 136.5, 139.4, 157.9, 165.7, 177.5,
201.1.
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Acknowledgments
We thank the National Institute of Health for financial
support (research grant GM 38907 to W.R.R., and
postdoctoral fellowship GM 20278 to N.A.P.).
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