Stereocontrolled formation of highly substituted cis-decalins via INOC annulation. An access to the branimycin core

Article abstract of DOI:10.1016/j.tet.2007.02.126

Quinic acid was used as a chiral scaffold for elaborating the highly substituted cis-decalin core system of branimycin via an Eschenmoser-Ireland rearrangement-INOC annulation sequence.

Full text of DOI:10.1016/j.tet.2007.02.126

Tetrahedron 63 (2007) 5930–5939
Stereocontrolled formation of highly substituted cis-decalins via
INOC annulation. An access to the branimycin core
*
Valentin S. Enev, Martina Drescher and Johann Mulzer
*
Institut fu€r Organische Chemie, Wa€hringerstrasse 38, A-1090 Wien, Austria
Received 16 January 2007; revised 27 February 2007; accepted 28 February 2007
Available online 3 March 2007
Abstract—Quinic acid was used as a chiral scaffold for elaborating the highly substituted cis-decalin core system of branimycin via an
Eschenmoser–Ireland rearrangement-INOC annulation sequence.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
from known ketone 2, readily available from (ꢀ)-quinic
acid.7
Branimycin, an unusual member of the nargenicin antibiotic
family,1 was isolated from Streptomyces and structurally
characterised by the Laatsch group.2 Preliminary biological
tests have shown that branimycin is highly active against
Streptomyces viridochromogenes. The structure of branimy-
cin has been reliably elucidated by multidimensional 1H and
13C NMR experiments. The interesting biological activity,
combined with the complex highly oxygenated cis-fused
decaline core, the 1,4-oxygen bridge and the macrolide
ring present is of considerable challenge for total synthesis.
For a successful synthesis two key obstacles had to be over-
come. Firstly, it had turned out that ketone 2 is resistant
towards direct alkylation via its lithium enolate,7 so the
introduction of the methylene-methoxy side chain was a crit-
ical point in our synthesis. Secondly, it was not clear whether
we could convert aldehyde A4 to the corresponding oxime
without isomerisation of the cis double bond.
We started with the conversion of ketone 2 into the silyl-enol
ether 37 (Scheme 1). The high reactivity of 3 towards suitable
electrophiles (NBS, m-CPBA)7 prompted us to try introduc-
tion of the methylene-methoxy group under Mukaiyama
conditions.8 After intensive investigation we found, that
compound 3 reacts with dimethoxy-ethane in the presence
of 5 mol % TMSOTf9 to give 4 as a single diastereomer in
55% yield (73% after recycling of the starting material).
The relative stereochemistry of 4 was assigned on the basis
The retrosynthetic concept is shown in Figure 1. As a key dis-
connection the 1,2-addition of vinyllithium subunit B3 to
bicyclic ketone A4,5 was envisaged. This highly convergent
approach necessitates efficient synthesis of both A and B.
2. Results and discussion
3
of the small J coupling constant of 3.9 Hz between H-5
Encouraged by recent model studies,4 we concentrated on
the fully substituted core compound A. Our retrosynthetic
plan based on using an intramolecular nitrile oxide olefin
cyclisations (INOC reaction),6 a useful method for the con-
struction of cis-decalin system, in intermediate A2, which
after Claisen rearrangement following reductive cleavage
of the N–O bond could give b-hydroxy compound A1. Ac-
cordingly, intermediate A2 was identified as a key synthetic
target. Antithetic disconnection leads to nitrile oxide A3 an
expected product from cis-unsaturated aldehyde A4. In turn,
aldehyde A4 would be assembled in stereoselective fashion
(known axial orientation due to the bis-ketal protecting
group) and H-6 and was secured by NOE experiments. At-
tempts to improve the yield by longer reaction times resulted
in epimerisation of 4. Reduction of 4 gave alcohol 1 stereo-
selectively, which was esterified with BnOCH2COOH under
Mitsunobu conditions to give the protected glycolate ester 5
in 93% yield. In the next step chelation-controlled glycolate
enolate Claisen rearrangement10 led to acid 6 as a single iso-
mer in 91% yield. (The stereochemistry of 6 was confirmed
by transformation of the corresponding Bn protected acid to
lactone 6a and NOE experiments). Formation of the methyl
ester followed by DIBAH reduction afforded aldehyde 7,
which was subjected to Still–Gennari olefination. The result-
ing (Z)-a,b-enoate was reduced to the alcohol and reoxidised
to aldehyde 8 in 76% yield.
Keywords: Branimycin; Natural products; Total synthesis; INOC reaction.
* Corresponding authors. Tel.: +43 1 4277 52190; fax: +43 1 4277 52189;
e-mailaddresses:valentin.enev@univie.ac.at; johann.mulzer@univie.ac.at
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.02.126

V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
5931
OMe
OH
OTMS
O
MeO
O
18
ref[7]
7
Macrolactonisation
1
a
b
17
21
15
2
1
5
3
1,2 addition
O
O
O
O
13
O
1
MeO
MeO
HO
20
OMe
H
11
3
MeO
19
MeO
MeO
9
H
HO
4
3
7
H
5
O
O
OMe
OPG3
OPG4
Branimycin
MeO
O
MeO
O
O
OPMB
c
OPG
O
1 H
d
H
2
OH
COOH
MeO
O
3
8
7
13
5
O
OPMB
O
MeO
MeO
Li
O
H
MeO
MeO
B
A
5
6
OH
O
O
N
O
H
MeO
MeO
O
H
H
OR3
11
MeO
MeO
MeO
10
g, h
e, f
H
H
O
O
CHO
8
H
O
O
MeO
O
OR2
OPMB
OPMB
O
O
MeO
MeO
OMe
OMe
MeO
MeO
A1
A2
8
7
1,3 dipolar
cycloaddition
OH
O-
N+
i
N
MeO
HO
MeO
O
H
MeO
MeO
H
MeO
OBn
H
O
O
O
H
H
O
OPMB
MeO
O
O
OR2
MeO
O
OR2
O
NOE
OMe
MeO
MeO
6a
9
A4
A3
Scheme 1. (a) CH2(OMe)2, TMSOTf, 2,6-di-tert-butyl-pyridine, 55%;
(b) NaBH4/CeCl3, quant; (c) PPh3, DEAD, PMBOCH2COOH, THF/
CH2Cl2, 0 ꢁC, 24 h, 93%; (d) LiHMDS/TMSCl, THF, ꢀ78 to 0 ꢁC, 91%;
(e) TMSCHN2, Tol/MeOH; (f) DIBAH, CH2Cl2, ꢀ78 ꢁC, 3.5 h, 80%; (g)
(CF3CH2O)2P(O)CH2CO2Me, KHMDS, Crown-6, THF, ꢀ78 ꢁC, 88%; (h)
i. DIBAH, ii. DMP/NaHCO3, 86% and (i) NH2OH$HCl, 2,6-di-tert-butyl-
O
O
OH
OH
HO2C
HO
MeO
MeO
O
O
OH
MeO
O
OH
˚
pyridine, MS 4 A, 60%.
OMe
OMe
(-)-quinic acid
2
1
Figure 1.
with NaBH4 to give alcohol 12. For the completion of the
A1 skeleton, alcohol 12 was subjected to a Claisen–Eschen-
moser rearrangement to give amide 13 in 82% yield.
The next problem was the conversion of 8 to the oxime with-
out isomerisation of the double bond. After testing a variety
of conditions we found that hydroxylamine hydrochloride in
With intermediate 13 in hand, the reductive cleavage of the
isoxazoline ring to the corresponding b-hydroxy compound
was attempted. Unfortunately, exposure of 13 to hydrogen in
the presence of Raney-Ni and boronic acid12 resulted in hy-
drogenation of the double bond and epimerisation at C-3 to
furnish compound 14 as an inseparable diastereomeric mix-
ture. This highly undesirable result was interpreted via an
imine–enamine tautomerisation13 followed by reduction
(Scheme 3).
˚
the presence of molecular sieves (4 A) and 3 equiv of poly-
mer-supported 2,6-di-tert-butyl-pyridine converted 8 into
a separable mixture of 60% cis-a,b-unsaturated oxime 9
and 5% of the trans-isomer. Aldehyde recovered unchanged
was 20%.
The stage was now set for the construction of bicyclic system
A2 (Scheme 2). The INOC reaction was initiated by heating
oxime 9 with 1.1 equiv NCS and a catalytic amount of pyri-
dine.11 The resulting nitrile oxide immediately formed isox-
azoline 10 in 92% yield. The configuration of 10 was secured
by NOE experiments. Removal of the PMB group furnished
alcohol 11, which was oxidised to the ketone and reduced
Several conditions were investigated to suppress the forma-
tion of the enamine such as variation of the catalysts (Pd/C,14
Rh/CaCO3, Lindlar catalyst15 and SmI216) and Lewis and
Brønsted acids (AlCl3,12 BF3$Et2O, 1 N HCl), however
without success.

5932
V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
MeO
O
O
O
N
MeO
O
O
MeO
O
N
MeO
O
O
N
H
H
H
H
H
H
H
H
a
b
9
O
a
b
11
O
O
OPMB
O
O
OH
OBn
OBn
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
11
10
15
16
O
NMe2
Scheme 4. (a) BnBr, NaH, THF/DMF, 87% and (b) Mo(CO)6, MeCN/H2O,
reflux, 82%.
MeO
O
N
MeO
O
O
O
N
H
H
H
e
c, d
MeO
O
O
O
N
MeO
O
O
O
N
O
H
H
H
H
H
OH
OH
O
O
O
OH
MeO
b
a
MeO
10
MeO
MeO
OPMB
OPMB
13
12
MeO
MeO
MeO
MeO
O
O
NMe2
18
MeO HO
17
H
H
f
TMSO
O
HO
O
H
H
H
O
O
O
O
O
MeO
MeO
MeO
MeO
c
MeO
d
O
O
O
MeO
H
O
OPMB
O
OPMB
14
MeO
MeO
Scheme 2. (a) NCS, pyridine, CHCl3, 60 ꢁC, 92%; (b) DDQ, CH2Cl2, 77%;
20
19
˚
(c) DMP, 89%; (d) NaBH4, CeCl3, 96%; (e) Me2NCH(OMe)2, MS 4 A,
xylene, 155 ꢁC, 82% and (f) H2, Raney-Ni, H3BO3.
HO
H
TMSO
O
O
MeO
e
At this point, we decided to step back and to perform the
Claisen–Eschenmoser rearrangement after the cleavage of
N–O bond of isoxazoline ring. Accordingly, alcohol 11
was benzylated and the resulting benzyl ether 1517 was
treated with Mo(CO)6 in refluxing acetonitrile.18 Unfortu-
nately, the formation of the desired a,b-enone was immedi-
ately followed by an intramolecular Michael addition to
afford the cyclic ether 16 in an 82% yield (Scheme 4).
O
H
O
OPMB
MeO
OMe
21
Scheme 5. (a) 2 equiv OsO4, pyridine, ꢀ25 ꢁC, 86%; (b) Me2C(OMe)2, PTS,
48 h, 97%; (c) H2, Raney-Ni, H3BO3, 0.5 h, 90%; (d) TMSOTf, 2,6-lutidine,
CH2Cl2, ꢀ78 ꢁC, 56%and(e)vinylmagnesiumbromide,THF, ꢀ78 ꢁC, 72%.
MeO HO
NH2
MeO HO
NH
H
H
H
H
NMe2
NMe2
H2/Ni
13
O
O
O
O
O
O
MeO
MeO
MeO
MeO
MeO HO
NH
MeO HO
O
H
H
H
H
NMe2
NMe2
14
O
O
O
O
O
O
MeO
MeO
MeO
Scheme 3. Presumptive formation of 14.
MeO
To suppress the formation of 16, the double bond in 10 was
converted into diol19 17 stereoselectively, which was pro-
tected as acetonide 18. Now, the cleavage of the isoxazoline
proceeded smoothly to give b-hydroxy ketone 19 in 92%
yield. Protection as TMS ether 20 and addition of
vinylmagnesium bromide furnished adduct 21 (72%) with
high stereoselectivity (Scheme 5).
In conclusion, we have shown that quinic acid may be used
as a chiral scaffold for elaborating the highly substituted

V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
5933
cis-decalin core system of branimycin via an Eschenmoser–
Ireland rearrangement-INOC annulation sequence. All re-
actions proceed with high stereo- and regiocontrol in
reasonable yields. Work towards the completion of the
synthesis is well underway in our labs.
99.92 (s), 69.32 (d), 69.09 (t), 66.07 (d), 59.16 (q), 50.23
(d), 47.98 (q), 47.94 (q), 17.76 (q), 17.59 (q); IR (Si, film)
nmax¼3346, 2950, 2833, 1683, 1619, 1455, 1110, 1012,
931, 901, 611, 571; MS (EI, 70 eV, 40 ꢁC): m/z¼255, 218,
197, 176, 154, 138, 123, 101, 73, 55; HRMS (EI, 70 eV,
60 ꢁC) calcd for C13H19O5 (M+ꢀMeOH): 255.1232, found:
255.1236.
3. Experimental section
3.1. General
3.1.2. Compound 1. A solution of ketone 4 (3 g, 10.5 mmol)
in MeOH (50 mL) was cooled to 0 ꢁC, CeCl3 (0.47 g,
1.3 mmol) was added and the solution was stirred for
15 min. NaBH4 (0.47 g, 12.5 mmol) was added in three
portions and after 15 min the reaction was quenched with
NH4Cl. The solvent was removed under reduced pressure
and the residue was hydrolysed with H2O (20 mL) and
EtOAc (100 mL). The two phases were separated and the
aqueous phase was extracted with EtOAc (2ꢂ25 mL). The
combined organic layers were washed with brine, dried
over MgSO4 and the solvent was removed under reduced
Reactions were conducted in flame-dried or oven-dried
glassware under an atmosphere of dry argon. All solvents
used in reactions were purified before use. Diethyl ether
and 1,2-dimethoxyethane were distilled from LiAlH4. Tetra-
hydrofuran was distilled from molten potassium metal.
Dichloromethane (DCM) and pyridine were distilled from
CaH2. Toluene was distilled over molten sodium metal.
Commercially available reagents were used without further
purification unless otherwise specified. Flash column
chromatography was performed with Merck silica gel 60
(230–400 mesh). Thin layer chromatography (TLC) was
performed on Merck silica gel 60 F254 plates. Compounds
were visualised with UV light, and/or ceric ammonium
molybdate. Melting points (mp) were measured on a Kofler
apparatus and are uncorrected. Infrared spectra were re-
corded with films on single-crystal silica plates using a Per-
kin–Elmer FT 1600 spectrometer and are reported in wave
numbers (cmꢀ1) with broad signals denoted by (br). NMR
spectra were recorded at 300 K on Avance spectrometers
(Bruker Biospin GmbH, Rheinstetten, Germany), i.e., DPX
250, DRX 400 WB, or DRX 600. Residual CHCl3 signal
1
pressure to give 1 (3.1 g, 100%) as a colourless oil. H
NMR (400.13 MHz, CDCl3): d¼5.71 (1H, H(2), dddd,
J¼10.3, 2.5, 2.3, 1.2), 5.54 (1H, H(3), ddd, J¼10.2, 2.3,
1.8), 4.57 (1H, H(1), m, J¼5.6, 5.2, 2.9, 2.3, 2.3), 4.12 (1H,
H(4), m, J¼9.0, 2.9, 2.5, 1.8, 0.5), 3.84 (1H, OH, d,
J¼5.2), 3.78 (1H, H(5), dd, J¼9.0, 2.8), 3.77 (1H, H(7),
dd, J¼9.3, 3.9), 3.63 (1H, H(7), dd, J¼9.3, 9.1), 3.35 (3H,
CH3O(7), s), 3.23 (3H, CH3O(4), s), 3.21 (3H, CH3O(5), s),
2.57 (1H, H(6), m, J¼9.1, 5.6, 3.9, 2.8, 1.3, 0.5), 1.28 (3H,
CH3, s), 1.27 (3H, CH3, s); 13C NMR (100.61 MHz,
CDCl3): d¼132.63 (d), 125.01 (d), 100.33 (s), 100.27 (s),
70.45 (d), 68.93 (t), 68.45 (d), 65.73 (d), 58.93 (q), 47.81
(q), 47.76 (q), 42.08 (d), 17.81 (q), 17.66 (q); IR (Si, film)
nmax¼3476, 2992, 2949, 2900, 2833, 1456, 1376, 1130,
1042, 933; MS (EI, 70 eV, 60 ꢁC): m/z¼257, 225, 156, 140,
101, 78, 55. HRMS (EI, 70 eV, 60 ꢁC) calcd for C13H21O5
(M+ꢀMeOH): 257.1389, found: 257.1384.
1
was used as an internal reference for H (d¼7.26 ppm), for
13C the CDCl3 carbon was adjusted to 77.00 ppm. 13C
NMR spectra were measured J-modulated and proton de-
coupled. The assignment was accomplished by standard 2D
NMR techniques (the numbering is according to Scheme 1
or starting from compound 10 to branimycin). The analysis
of the coupling constants (J, in hertz) was supported by the
software SpinWorks (provided by Kirk Marat, University
of Manitoba, Canada). Mass spectra (MS) were recorded
on a Finnigan (MAT 8230, 9008) machine.
3.1.3. Compound 5. A solution of the alcohol 1 (2.6 g,
9.0 mmol) in THF (70 mL) and DCM (70 mL) was cooled
to 0 ꢁC. Ph3P (8.2 g, 31.3 mmol) and 5 min later p-methoxy-
benzyloxy acetic acid (2.8 g, 14.3 mmol) were added. After
additional 5 min, DEAD (7.2 mL, 45 mmol) was added drop-
wise and the reaction mixture was stirred for 30 min at 0 ꢁC.
Then the solution was stored in the refrigerator at +4 ꢁC for
24 h. The reaction mixture was diluted with toluene
(80 mL) and concentrated under reduced pressure. The crude
product was purified by column chromatography to yield
3.1.1. Compound 4. To a solution of 3 (13.0 g, 41.3 mmol)
in DCM (80 mL) 2,6-di-tert-butyl-pyridine (0.94 mL,
4.2 mmol) and dimethoxymethane (6.3 g, 82.9 mmol)
were added and the reaction mixture was cooled to 0 ꢁC.
TMSOTf (0.756 mL, 4.2 mmol) was added dropwise, the
reaction was stirred for 2 h at 0 ꢁC and quenched with a sat-
urated NaHCO3 solution. The phases were separated and
extracted with DCM (3ꢂ70 mL). The organic phase was
dried over MgSO4 and the solvent was removed under re-
duced pressure. The crude product was purified by HPLC
to yield 4 (6.5 g, 55%) as the desired product and 5.2 g
of starting material. 1H NMR (400.13 MHz, CDCl3):
d¼6.81 (1H, H(3), dd, J¼10.1, 1.8), 5.99 (1H, H(2), ddd,
J¼10.2, 2.6, 0.7), 4.88 (1H, H(4), ddd, J¼9.4, 2.6, 1.7),
4.16 (1H, H(5), dd, J¼9.4, 6.4), 3.87 (1H, H(7), dd,
J¼9.2, 3.9), 3.76 (1H, H(7), dd, J¼9.2, 3.9), 3.29 (3H,
CH3O(4), s), 3.28 (3H, CH3O(7), s), 3.23 (3H, CH3O(5),
s), 2.71 (1H, H(6), dddd, J¼6.4, 3.9, 3.9, 0.7), 1.34 (3H,
CH3, s), 1.32 (3H, CH3, s); 13C NMR (100.61 MHz,
CDCl3): d¼198.79 (s), 148.53 (d), 129.85 (d), 100.66 (s),
1
5 (3.9 g, 93%). H NMR (400.13 MHz, CDCl3): d¼7.28
(2H, H(ar), d, J¼8.6), 6.87 (2H, H(ar), d, J¼8.6), 5.86–5.78
(2H, H(2,3), m), 5.50 (1H, H(1), m), 4.55 (2H, OCH2(ar),
s), 4.16 (1H, H(4), m), 4.03 (1H, H(7), dd, J¼9.7, 4.7),
4.02 (1H, C(O)CH2, d, J¼16.5), 4.00 (1H, C(O)CH2, d,
J¼16.5), 3.80 (3H, CH3O(ar), s), 3.74 (1H, H(5), dd, J¼
9.4, 3.4), 3.34 (3H, CH3O(7), s), 3.29 (1H, H(7), dd, J¼9.7,
9.5), 3.24 (3H, CH3O, s), 3.21 (3H, CH3O, s), 2.28
(1H, H(6), m), 1.31 (3H, CH3, s), 1.28 (3H, CH3, s); 13C
NMR (100.61 MHz, CDCl3): d¼169.68 (s), 159.45 (s),
131.83 (d), 129.68 (2ꢂd), 129.18 (s), 124.75 (d), 113.85
(2ꢂd), 100.46 (s), 100.30 (s), 72.87 (t), 70.10 (d), 67.97 (t),
66.80 (t), 66.39 (d), 65.31 (d), 58.94 (q), 55.24 (q), 47.84
(q), 47.77 (q), 42.29 (d), 17.79 (q), 17.73 (q); HRMS (EI,
70 eV, 60 ꢁC) calcd for C24H34O9 (M+): 466.2203, found:
466.2196.

5934
V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
3.1.4. Compound 6. Toa solution of 5 (0.92 g, 1.97 mmol) in
THF (47 mL) was added at ꢀ78 ꢁC TMSCl (1.18 mL and 3
drops of triethylamine). After 5 min LiHMDS (6.8 mL of
1 M solution in toluene) was added and stirring was contin-
ued for 30 min at ꢀ78 ꢁC and 2 h at room temperature. The
reaction was quenched with water and the pH was adjusted
to 3 (HCl concd). The phases were separated and extracted
with EtOAc (3ꢂ50 mL), and the organic phases were com-
bined and washed with brine, dried over MgSO4 and the sol-
vent was removed under reduced pressure. The crude product
1586, 1514, 1463, 1374, 1174, 1220, 1174, 1038,
884 cmꢀ1; MS (EI, 70 eV) m/e (relative intensity): 465
(M+ꢀCH3OH, 0.3), 347 (0.6), 312 (1.5), 282 (1.5), 121
(100); HRMS (EI, 70 eV, 60 ꢁC) calcd for C24H33O9
(M+ꢀCH3): 465.2125, found: 465.2133.
DIBAH (1.4 mL, 1.5 M solution) was added dropwise to
a solution of the ester (0.66 g, 1.4 mmol) in DCM (16 mL)
at ꢀ78 ꢁC. After 3.5 h at ꢀ78 ꢁC the reaction was quenched
with methanol (1 mL) and a saturated solution of aqueous
sodium-potassium tartarate (50 mL) was added. The mixture
was stirred overnight at room temperature. The phases were
separated and the aqueous phase was extracted with DCM
(3ꢂ30 mL). The combined organic layers were dried over
MgSO4 and the solvent was removed under reduced pres-
sure. The crude product was purified by flash chromato-
graphy to give aldehyde 7 (0.50 g, 80%) and unreacted
ester (0.12 g, 18%). 1H NMR (400.13 MHz, CDCl3):
d¼9.72 (1H, H(9), d, J¼1.2), 7.29 (2H, H(ar), d, J¼8.8),
6.86 (2H, H(ar), d, J¼8.8), 5.92 (1H, H(1), ddd, J¼10.0,
5.2, 1.8), 5.58 (1H, H(2), ddd, J¼10.0, 4.6, 1.2), 4.59 (1H,
OCH2(ar), d, J¼11.5), 4.53 (1H, OCH2(ar), d, J¼11.5),
4.48 (1H, H(5), dd, J¼11.2, 6.9), 4.03 (1H, H(4), dd,
J¼11.2, 7.4), 3.80 (3H, CH3O(ar), s), 3.78 (1H, H(8), dd,
J¼2.5, 1.2), 3.74 (1H, H(7), dd, J¼9.0, 4.2), 3.37 (1H,
H(7), dd, J¼8.9, 8.8), 3.43 (3H, CH3O(7), s), 3.14 (3H,
CH3O, s), 3.12 (3H, CH3O, s), 3.06 (1H, H(3), m), 2.61
(1H, H(6), m), 1.23 (6H, 2ꢂCH3, s); 13C NMR
(100.61 MHz, CDCl3): d¼204.36 (d), 159.22 (s), 130.90
(d), 130.06 (s), 129.01 (2ꢂd), 125.91 (d), 113.67 (2ꢂd),
99.53 (s), 99.14 (s), 84.15 (d), 73.30 (t), 72.51 (t), 65.82
(d), 65.67 (d), 59.03 (q), 55.28 (q), 47.84 (q), 47.53 (q),
44.88 (d), 39.22 (d), 17.73 (q), 17.66 (q); IR (Si, film)
nmax¼2926, 2833, 1730, 1613, 1586, 1515, 1463, 1375,
1195, 1137, 1082, 963, 886 cmꢀ1; MS (EI, 70 eV) m/e (rel-
ative intensity): 418 (M+ꢀCH3OH, 1), 309 (0.5), 282 (1.5),
121 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd for C23H30O7
(M+ꢀCH3OH): 418.1991, found: 418.1998.
1
was filtered through silica gel to give 6 (0.84 g, 91%). H
NMR (400.13 MHz, CDCl3): d¼w8.3 (CO2H, very br),
7.23 (2H, H(ar), d, J¼8.8), 6.87 (2H, H(ar), d, J¼8.8), 5.97
(1H, H(1), ddd, J¼10.0, 5.2, 1.7), 5.64 (1H, H(2), ddd,
J¼10.0, 4.6, 1.2), 4.55 (1H, OCH2(ar), d, J¼10.6), 4.52
(1H, OCH2(ar), d, J¼10.6), 4.48 (1H, H(5), dd, J¼11.3,
6.8), 4.10 (1H, H(4), dd, J¼11.3, 7.3), 4.04 (1H, H(8), d,
J¼2.1), 3.80 (3H, CH3O(ar), s), 3.74 (1H, H(7), dd, J¼8.9,
4.1), 3.38 (1H, H(7), dd, J¼8.9, 8.4), 3.35 (3H, CH3O(7),
s), 3.18 (1H, H(3), m), 3.18 (3H, CH3O, s), 2.96 (3H,
CH3O, s), 2.62 (1H, H(6), m), 1.21 (3H, CH3, s), 1.20 (3H,
CH3, s); 13C NMR (100.61 MHz, CDCl3): d¼172.58 (s),
159.74 (s), 131.41 (d), 129.78 (2ꢂd), 128.69 (s), 125.94
(d), 113.93 (2ꢂd), 99.35 (s), 99.29 (s), 78.75 (d), 74.43 (t),
72.29 (t), 65.68 (d), 65.39 (d), 59.04 (q), 55.30 (q), 48.00
(q), 47.39 (q), 42.19 (d), 39.25 (d), 17.54 (q), 17.09 (q).
3.1.5. Compound 6a. 1H NMR (400.13 MHz, CDCl3):
d¼7.42–7.29 (5H, H(ar), m), 5.79 (1H, H(2), dddd, J¼
10.4, 2.9, 2.9, 1.0), 5.72 (1H, H(1), dddd, J¼10.4, 1.7, 1.7,
1.6), 4.97 (1H, OCH2(ar), d, J¼12.2), 4.80 (1H, OCH2(ar),
d, J¼12.2), 4.53 (1H, H(4), ddd, J¼4.8, 4.8, 1.0), 4.39 (1H,
H(5), ddd, J¼4.8, 4.3, 1.6), 4.33 (1H, H(8), d, J¼7.8), 3.77
(1H, H(7), dd, J¼9.5, 3.4), 3.73 (1H, H(7), dd, J¼9.5, 4.7),
3.54 (1H, OH, br s), 3.39 (3H, CH3O, s), 3.28 (1H, H(3),
m, J¼7.8, 4.8, 3.0, 2.9, 1.6), 2.56 (1H, H(6), m, J¼4.7, 4.3,
3.4, 3.0, 2.9, 1.7); 13C NMR (100.61 MHz, CDCl3):
d¼174.13 (s), 136.80 (s), 128.59 (2ꢂd), 128.19 (d), 128.02
(2ꢂd), 127.65 (d), 122.16 (d), 75.08 (d), 74.98 (d), 74.56
(t), 72.67 (t), 67.51 (d), 59.41 (q), 36.64 (d), 35.36 (d).
3.1.7. Compound 8. A solution of O,O0-bis-(2,2,2-trifluoro-
ethyl)-(methyoxy-carbonylmethyl)-phosphonate (0.21 mL,
0.98 mmol), 18-crown-6-ether (1.55 g, 5.9 mmol) and
KHMDS (2 mL, 0.5 M solution) in THF (11 mL) was stirred
at ꢀ78 ꢁC for 75 min. The reaction mixture was cooled
to ꢀ90 ꢁC and a solution of 7 (2.18 g, 4.84 mmol) in THF
(10 mL) was added dropwise. After 3 h at ꢀ90 ꢁC and 3 h
at ꢀ80 ꢁC the reaction was quenched with saturated NH4Cl
solution and warmed to room temperature. The phases
were separated and the aqueous phase was extracted with di-
ethyl ether (3ꢂ30 mL). The combined organic layers were
dried over MgSO4 and concentrated in vacuo. The residue
was purified by column chromatography on silica gel to ob-
3.1.6. Compound 7. A mixture of 6 (0.66 g, 1.4 mmol) in
toluene/methanol, 5:1 (10 mL) and trimethylsilyldiazo-
methane (1 mL, 2 M solution) was stirred at room tempera-
ture until the starting material was consumed. The solvent
was removed under reduced pressure and the methyl ester
(0.67 g, 99%) was used without further purification. 1H
NMR (600.13 MHz, CDCl3): d¼7.30 (2H, H(ar), d, J¼
8.8), 6.84 (2H, H(ar), d, J¼8.8), 5.85 (1H, H(1), ddd,
J¼10.0, 5.0, 1.5), 5.54 (1H, H(2), ddd, J¼10.0, 4.9, 1.0),
4.68 (1H, OCH2(ar), d, J¼11.2), 4.39 (1H, OCH2(ar), d,
J¼11.2), 4.31 (1H, H(5), dd, J¼11.2, 6.9), 4.11 (1H, H(8),
d, J¼3.0), 4.06 (1H, (H4), dd, J¼11.2, 7.1), 3.80 (3H,
CH3O(ar), s), 3.74 (1H, H(7), dd, J¼8.9, 4.2), 3.70 (3H,
CO2CH3, s), 3.37 (1H, H(7), dd, J¼8.9, 8.9), 3.34 (3H,
CH3O(7), s), 3.19 (3H, CH3O, s), 3.15 (3H, CH3O, s), 3.09
(1H, H(3), m), 2.58 (1H, H(6), m), 1.23 (3H, CH3, s), 1.22
(3H, CH3, s); 13C NMR (100.61 MHz, CDCl3): d¼172.53
(s), 159.06 (s), 130.48 (d), 130.45 (s), 129.27 (2ꢂd),
125.63 (d), 113.50 (2ꢂd), 99.09 (s), 98.97 (s), 77.78 (d),
72.68 (t), 72.59 (t), 65.75 (d), 65.50 (d), 59.01 (q), 55.27
(q), 51.34 (q), 47.68 (q), 47.57 (q), 43.01 (d), 39.28 (d),
17.76 (q), 17.57 (q); IR (Si, film) nmax¼2948, 1751, 1613,
1
tain the (Z)-enoate (2.15 g, 88%). H NMR (600.13 MHz,
CDCl3): d¼7.26 (2H, H(ar), d, J¼8.6), 6.84 (2H, H(ar), d,
J¼8.6), 6.26 (1H, H(9), dd, J¼11.7, 9.8), 5.89 (1H, H(10),
dd, J¼11.7, 1.0), 5.88 (1H, H(1), ddd, J¼10.1, 5.0, 1.4),
5.79 (1H, H(2), ddd, J¼10.1, 4.7, 1.0), 5.54 (1H, H(8), ddd,
J¼9.8, 3.7, 1.0), 4.45 (1H, OCH2(ar), d, J¼11.3), 4.44 (1H,
OCH2(ar), d, J¼11.3), 4.13 (1H, H(5), dd, J¼11.5, 6.7),
4.02 (1H, H(4), dd, J¼11.5, 7.2), 3.79 (3H, CH3O(ar),
s), 3.74 (1H, H(7), dd, J¼8.9, 4.2), 3.71 (3H, CO2CH3, s),
3.36 (1H, H(7), dd, J¼8.9, 8.9), 3.34, (3H, CH3O(7), s),
3.21 (3H, CH3O(4), s), 3.12 (3H, CH3O(5), s), 2.99 (1H,

V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
5935
H(3), m), 2.58 (1H, H(6), m), 1.213 (3H, CH3, s), 1.12 (3H,
CH3, s); 13C NMR (100.61 MHz, CDCl3): d¼166.09 (s),
158.89 (s), 148.14 (d), 131.42 (s), 129.75 (d), 128.97
(2ꢂd), 125.76 (d), 120.81 (d), 113.55 (2ꢂd), 98.94 (s),
98.84 (s), 73.36 (d), 72.76 (t), 70.67 (t), 65.54 (d), 65.50
(d), 59.01 (q), 55.26 (q), 51.00 (q), 47.74 (q), 47.23 (q),
44.64 (d), 39.52 (d), 17.64 (q), 17.63 (q); IR (Si, film)
nmax¼2948, 1731, 1613, 1514, 1434, 1374, 1174, 1123,
1039, 823 cmꢀ1; MS (EI, 70 eV) m/e (relative intensity):
474 (M+ꢀCH3OH, 0.4), 443 (0.2), 360 (0.5), 338 (5), 121
(100); HRMS (EI, 70 eV, 60 ꢁC) calcd for C26H34O8
(M+ꢀCH3OH): 474.2254, found: 474.2261.
(t), 72.17 (d), 70.39 (t), 65.45 (d), 65.29 (d), 59.01 (q),
55.28 (q), 47.85 (q), 46.88 (q), 44.64 (d), 44.14 (d), 39.56
(d), 17.80, (q), 17.50 (q); IR (Si, film) nmax¼2946, 1738,
1680, 1613, 1514, 1373, 885, 822 cmꢀ1; MS (EI, 70 eV) m/
e (relative intensity): 476 (M+, 0.5), 445 (1), 338 (3), 207
(10), 121 (100), 101 (25); HRMS (EI, 70 eV, 60 ꢁC) calcd
for C25H33O7 (M+ꢀOMe): 445.2226, found: 445.2235.
3.1.8. Compound 9. A mixture of 8 (1.88 g, 3.96 mmol),
hydroxylamine hydrochloride (1 g, 15.8 mmol) and 2,6-di-
tert-butyl-pyridine polymer supported (10.9 g, 19.8 mmol)
in THF (200 mL) was stirred at 40 ꢁC for 24 h. After cool-
ing, the mixture was diluted with toluene and filtered
through a Celite pad. The solvent was removed under re-
duced pressure and the residue was purified by column
chromatography to obtain 9 (1.22 g, 61%), the trans-oxime
A solution of the (Z)-enoate (1.36 g, 2.69 mmol) in DCM
(30 mL) was cooled to ꢀ78 ꢁC and DIBAH (6.2 mL of 1 M
solution) was added dropwise. After 5 h the reaction was
quenched with methanol, diluted with saturated aqueous
potassium-sodium tartarate solution and stirred overnight at
room temperature. The phases were separated and the
aqueous phase was extracted with DCM (3ꢂ30 mL). The
combined organic layers were dried over MgSO4 and con-
centrated in vacuo to give the alcohol (1.29 g, quant). The
crude product was used without further purification. 1H
NMR (250 MHz, CDCl3): d¼7.22 (2H, d, J¼8.6), 6.85
(2H, d, J¼8.6), 5.92 (1H, dd, J¼10.5, 4.4), 5.89 (1H, dd,
J¼10.8, 3.8), 5.86 (1H, J¼10.5, 3.4), 5.43 (1H, dd, J¼10.8,
1.1), 4.67 (1H, dd, J¼10.6, 4.0), 4.42 (1H, t, J¼11.4), 4.40
(1H, d, J¼11.4), 4.21 (1H, d, J¼11.4), 4.14 (1H, dd, J¼11.6,
7.6), 4.06 (1H, dd, J¼11.6, 6.7), 3.86 (1H, m), 3.79 (3H, s),
3.71 (1H, dd, J¼8.9, 4.1), 3.44 (1H, dd, J¼11.0, 2.1), 3.37
(1H, t, J¼8.7), 3.34 (3H, s), 3.22 (3H, s), 3.20 (3H, s), 2.51
(1H, m), 1.27 (3H, s), 1.25 (3H, s); 13C NMR (100.6 MHz,
CDCl3): d¼159.38, 133.88, 131.36, 130.12, 129.60,
129.34, 125.82, 114.07, 100.11, 99.37, 73.01, 72.16, 69.55,
66.06, 59.41, 58.74, 55.66, 48.10, 47.86, 43.93, 39.84,
30.08, 18.23, 17.81; IR (Si, film) nmax¼3475, 2933, 2834,
1612, 1248, 1123, 1036, 845 cmꢀ1; MS (EI, 70 eV) m/e (rel-
ative intensity): 446 (M+ꢀCH3OH, 0.3), 415 (0.25), 360
(0.2), 121 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C25H34O7 (M+ꢀCH3OH): 446.2305, found: 446.2294.
1
(0.11 g, 5%) and unreacted 8 (0.36 g, 20%). 9: H NMR
(400.13 MHz, CDCl3): d¼8.15 (1H, H(11), dd, J¼10.4,
0.9), w8.1 (1H, OH, br s), 7.23 (2H, H(ar), d, J¼8.8),
6.87 (2H, H(ar), d, J¼8.8), 6.26 (1H, H(10), ddd, J¼11.2,
10.5, 0.8), 5.89 (1H, H(2), dd, J¼10.4, 4.8), 5.85 (1H,
H(1), dd, J¼10.4, 3.8), 5.75 (1H, H(9), ddd, J¼11.2,
10.3, 0.9), 4.76 (1H, H(8), dd, J¼10.3, 3.5), 4.40 (1H,
OCH2(ar), d, J¼11.2), 4.27 (1H, OCH2(ar), d, J¼11.2),
4.07 (1H, H(4), dd, J¼11.5, 6.8), 4.02 (1H, H(5), dd,
J¼11.5, 6.2), 3.80 (3H, CH3O(ar), s), 3.72 (1H, H(7), dd,
J¼8.9, 4.1), 3.36 (1H, H(7), dd, J¼8.9, 8.9), 3.34 (3H,
CH3O(7), s), 3.23 (3H, CH3O, s), 3.04 (1H, H(3), m),
3.04 (3H, CH3O, s), 2.55 (1H, H(6), m), 1.29 (3H, CH3,
s), 1.20 (3H, CH3, s); 13C NMR (100.61 MHz, CDCl3):
d¼159.05 (s), 149.06 (d), 136.85 (d), 130.65 (s), 129.74
(d), 129.13 (2ꢂd), 125.27 (d), 125.15 (d), 113.72 (2ꢂd),
99.26 (s), 98.73 (s), 73.12 (d), 72.67 (t), 69.86 (t), 65.38
(d), 65.14 (d), 58.98 (q), 55.26 (q), 47.77 (q), 47.66 (q),
44.23 (d), 39.46 (d), 17.66 (q), 17.63 (q); IR (Si, film)
nmax¼3345, 2947, 1613, 1514, 1463, 1376, 1122, 1040,
797, 733 cmꢀ1; MS (EI, 70 eV) m/e (relative intensity):
460 (M+ꢀCH3O, 3), 385 (2), 323 (10), 121 (100); HRMS
(EI, 70 eV, 60 ꢁC) calcd for C25H34O7N (M+ꢀCH3O):
460.2335, found: 460.2327.
To a slurry of Dess–Martin periodinane (2.2 g) and NaHCO3
(1.75 g) in DCM (30 mL) a solution of the alcohol (1.926 g,
4.03 mmol) in DCM (67 mL) was added dropwise at room
temperature and the mixture was stirred until the starting
material was consumed (TLC). The reaction mixture was
concentrated under reduced pressure and the residue was
purified by column chromatography on silica gel to give 8
3.1.9. Compound 10. A solution of 9 (0.61 g, 1.24 mmol),
NCS (0.168 g, 1.26 mmol) and pyridine (72 mL) in chloro-
form (20 mL) was heated for 10 min at 40 ꢁC and for 1 h
at 60 ꢁC. After removing the solvent under reduced pressure
water (50 mL) was added and the mixture was extracted with
DCM (3ꢂ50 mL). The combined extracts were dried
(MgSO4) and concentrated in vacuo. The residue was puri-
1
1
(1.88 g, 99%). H NMR (400.13 MHz, CDCl3): d¼10.01
fied by flash chromatography to give 10 (0.56 g, 92%). H
(1H, H(11), d, J¼8.2), 7.22 (2H, H(ar), d, J¼8.8), 6.87
(2H, H(ar), d, J¼8.8), 6.46 (1H, H(9), dd, J¼11.3, 10.4),
6.04 (1H, H(10), ddd, J¼11.3, 8.2, 0.8), 5.93 (1H, H(1),
ddd, J¼10.2, 5.1, 1.4), 5.87 (1H, H(2), ddd, J¼10.2, 4.2,
1.0), 5.22 (1H, H(8), dd, J¼10.4, 3.6), 4.49 (1H, OCH2(ar),
d, J¼11.3), 4.35 (1H, OCH2(ar), d, 11.3), 4.13 (1H, H(5),
dd, J¼11.6, 7.5), 3.96 (1H, H(4), dd, J¼11.6, 6.7), 3.80
(3H, CH3O(ar), s), 3.71 (1H, H(7), dd, J¼9.0, 4.1), 3.37
(1H, H(7), dd, J¼9.0, 8.4), 3.34 (3H, CH3O(7), s), 3.22
(3H, CH3O, s), 3.11 (1H, H(3), m), 3.01 (3H, CH3O, s),
2.55 (1H, H(6), m), 1.22 (3H, CH3, s), 1.20 (3H, CH3, s);
13C NMR (100.61 MHz, CDCl3): d¼192.18 (s), 159.26 (s),
149.16 (d), 131.95 (d), 130.43 (d), 130.06 (s), 129.18
(2ꢂd), 124.53 (d), 113.83 (2ꢂd), 99.17 (s), 98.95 (s), 72.39
NMR (400.13 MHz, CDCl3): (branimycin numbering)
d¼7.26 (2H, H(ar), d, J¼8.6), 6.87 (2H, H(ar), d, J¼8.6),
6.60 (1H, H(3), d, J¼10.0), 6.40 (1H, H(4), dd, J¼10.0,
5.3), 4.97 (1H, H(10), d, J¼10.6), 4.56 (1H, OCH2(ar), d,
J¼11.2), 4.52 (1H, OCH2(ar), d, J¼11.2), 4.42 (1H, H(5),
dd, J¼5.3, 1.6), 4.03 (1H, H(7), dd, J¼10.8, 10.6), 3.89
(1H, H(8), dd, J¼10.6, 4.5), 3.80 (3H, CH3O(ar), s), 3.74
(1H, H(11), dd, J¼10.6, 6.7), 3.53 (1H, H(20), dd, J¼9.5,
3.9), 3.42 (1H, H(20), dd, J¼9.5, 6.7), 3.33 (3H,
CH3O(20), s), 3.14 (3H, CH3O(7), s), 3.09 (3H, CH3O(8),
s), 2.96 (1H, H(6), ddd, J¼10.8, 6.7, 1.6), 2.14 (1H, H(9),
m), 1.17 (3H, CH3, s), 1.12 (3H, CH3, s); 13C NMR
(100.61 MHz, CDCl3): d¼159.38 (s), 156.67 (s), 135.55
(d), 130.33 (s), 129.38 (2ꢂd), 119.56 (d), 113.88 (2ꢂd),

5936
V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
100.33 (s), 99.90 (s), 80.28 (d), 70.95 (t), 69.12 (d), 68.69 (t),
65.99 (d), 65.21 (d), 58.91 (q), 55.29 (q), 47.56 (q), 47.52
(q), 44.10 (d), 42.48 (d), 35.16 (d), 17.66 (q), 17.63 (q); IR
(Si, film) nmax¼2946, 2055, 1891, 1613, 1585, 1514, 1455,
1376, 1249, 1106, 881 cmꢀ1; MS (EI, 70 eV) m/e (relative
intensity): 489 (M+, 2.5), 458 (1.5), 358 (1.5), 336 (2.5),
294 (2), 121 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C26H35O8 (M+): 489.2363, found: 489.2358.
at 0 ꢁC for 30 min. The reaction was diluted with saturated
aqueous NH4Cl (10 mL), EtOAc (10 mL) and saturated
aqueous NaCl (5 drops). The phases were separated and ex-
tracted with EtOAc (3ꢂ10 mL), dried over MgSO4 and the
solvent was removed under reduced pressure. The crude
was purified by flash chromatography to give alcohol 12
(0.48 g, 99%), white crystals, mp¼134.0–134.2 ꢁC (from
hexane). 1H NMR (400.13 MHz, CDCl3): (branimycin num-
bering) d¼6.39 (1H, H(3), dd, J¼10.2, 2.6), 6.33, (1H, H(4),
ddd, J¼10.2, 1.8, 0.8), 4.95 (1H, H(10), d, J¼10.2), 4.67
(1H, H(5), m), 4.29 (1H, H(7), dd, J¼10.5, 10.3), 4.28
(1H, OH, d, J¼11.8), 4.18 (1H, H(8), dd, J¼10.5, 4.7),
3.51 (1H, H(11), dd, J¼10.2, 6.0), 3.505 (1H, H(20), dd,
J¼9.5, 4.2), 3.48 (1H, H(20), dd, J¼9.5, 5.2), 3.33 (3H,
CH3O(20), s), 3.23 (3H, CH3O(7), s), 3.20 (1H, H(6), m),
3.13 (3H, CH3O(8), s), 2.13 (1H, H(9), ddd, J¼5.2, 4.7,
4.2), 1.24 (3H, CH3, s), 1.21 (3H, CH3, s); 13C NMR
(100.61 MHz, CDCl3): d¼155.82 (s), 144.01 (d), 115.76
(d), 101.08 (s), 100.19 (s), 80.05 (d), 70.76 (d), 68.71 (t),
68.13 (d), 66.67 (d), 58.94 (q), 48.21 (q), 47.71 (q), 46.97
(d), 44.04 (d), 36.04 (d), 17.81 (q), 17.70 (q); IR (Si, film)
nmax¼3460, 2930, 1415, 1114, 1064, 947, 847 cmꢀ1; MS
(EI, 70 eV) m/e (relative intensity): 369 (M+, 10), 338
(12), 280 (16), 238 (17), 221 (100), 176 (87), 160 (45),
130 (41), 101 (80); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C18H27O7N (M+): 369.1788, found: 369.1781.
3.1.10. Compound 11. A mixture of 10(0.190 g, 0.39 mmol)
and DDQ (0.180 g, 0.78 mmol) in DCM/phosphate buffer
pH¼7 (20 mL, 1:1) was sonificated in an ultrasound bath
for 2 h, diluted with saturated aqueous NaHCO3 and ex-
tracted with diethyl ether (3ꢂ30 mL). The organic phases
were dried (MgSO4) and the solvent was removed under
reduced pressure. The crude product was purified by flash
chromatography to give 11 (0.110 g, 77%). 1H NMR
(400.13 MHz, CDCl3): (branimycin numbering) d¼6.58
(1H, H(3), d, J¼10.0), 6.40 (1H, H(4), dd, J¼10.0, 4.9),
4.99 (1H, H(10), dd, J¼10.7, 1.5), 4.72, (1H, H(5), m), 4.12
(1H, H(7), dd, J¼10.6, 10.4), 3.89 (1H, H(8), dd, J¼10.6,
5.3), 3.73 (1H, H(11), dd, J¼10.7, 7.5), 3.56 (1H, H(20),
dd, J¼9.5, 4.2), 3.48 (1H, H(20), dd, J¼9.5, 6.1), 3.34 (3H,
CH3O(20), s), 3.20 (3H, CH3O, s), 3.11 (3H, CH3O, s),
2.89 (1H, H(6), ddd, J¼10.4, 7.5, 2.7), 2.15 (1H, H(9), m),
1.78 (1H, OH, d, J¼5.2), 1.20 (3H, CH3, s), 1.16, (3H,
CH3, s); 13C NMR (100.61 MHz, CDCl3): d¼155.12 (s),
137.39 (d), 119.05 (d), 100.21 (s), 99.83 (s), 80.20 (d), 68.80
(t), 65.81 (d), 65.43 (d), 63.51 (d), 58.90 (q), 47.72 (q), 47.64
(q), 43.83(d), 42.06(d), 37.86 (d), 17.86 (q), 17.64 (q); IR (Si,
3.1.12. Eschenmoser rearrangement to 13. A mixture of
˚
12 (0.28 g, 0.75 mmol) MS (0.1 g, 4 A) and Me2NH(OMe)2
(1 g, 9 mmol) in toluene was heated for 1 h at 110 ꢁC under
argon in a sealed tube. The mixture was cooled to room tem-
perature and an additional portion of Me2NH(OMe)2 (0.2 g)
was added and the mixturewas heated for 5 h at 155 ꢁC under
argon. During the additional 5 h of heating a further two por-
tions of reagent (0.2 g) were added. The mixture was filtered
through Celite and the residue was washed with EtOAc
(15ꢂ2 mL). The solvent was removed under reduced pres-
sure. The crude product was purified by flash chromato-
graphy to give 13 (0.27 g, 82%), as white crystals, mp
122.1–122.9 ꢁC (from hexane). 1H NMR (600.13 MHz,
CDCl3): (branimycin numbering) d¼5.92 (1H, H(5), ddd, J¼
10.1, 4.1, 2.9), 5.80 (1H, H(4), ddd, J¼10.1, 2.3, 2.3), 4.86
(1H, H(10), dd, J¼11.3, 3.5), 4.01 (1H, H(7), dd, J¼11.0,
9.1), 3.76 (1H, H(3), m), 3.755 (1H, H(8), dd, J¼11.0, 6.2),
3.64 (1H, H(11), ddd, J¼11.5, 10.3, 1.6), 3.61 (1H, H(20),
dd, J¼9.4, 5.1), 3.54 (1H, H(20), dd, J¼9.4, 5.2), 3.33 (3H,
CH3O(20), s), 3.22 (3H, CH3O(7), s), 3.19 (1H, H(6), m),
3.16 (3H, CH3O(8), s), 3.05 (1H, H(2), dd, J¼16.2, 5.4),
3.03 (3H, CH3N, s), 2.98 (3H, CH3N, s), 2.47 (1H, H(2),
dd, J¼16.2, 8.4), 2.19 (1H, H(9), dddd, J¼6.2, 5.2, 5.1,
3.5), 1.23 (3H, CH3, s), 1.22 (3H, CH3, s); 13C NMR (chem-
ical shifts from 2D HSQC spectrum, no quarternary carbons)
(150.90 MHz, CDCl3): d¼129.4 (d), 126.4 (d), 80.1 (d), 69.5
(t), 66.4 (d), 65.3 (d), 59.1 (q), 48.1 (q), 48.0 (q), 46.6 (d), 42.8
(d), 37.7 (q), 35.9 (q), 35.6 (t), 35.6 (d), 32.8 (d), 18.1 (2ꢂq);
IR (Si, film) nmax¼2946, 1735, 1650, 1459, 1112, 885,
849 cmꢀ1; HRMS (EI, 70 eV, 60 ꢁC) calcd for C22H34O7N2
(M+): 438.2366, found: 438.2370.
film) nmax¼3460, 2930, 1420, 1115, 1064, 945, 847 cmꢀ1
;
MS (EI, 70 eV) m/e (relative intensity): 369 (M+, 14), 338
(25), 280 (15), 263 (28), 238 (43), 221 (65), 176 (100), 160
(62), 130 (71), 101 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd
for C18H27O7N (M+): 369.1788, found: 369.1797.
3.1.11. Compound 12. To a slurry of Dess–Martin periodi-
nane (0.046 g) and NaHCO3 (0.05 g) in DCM (1 mL) a solu-
tion of 11 (0.05 g, 0.136 mmol) in DCM (1.8 mL) was added
dropwise at room temperature and the mixture was stirred
until the starting material was consumed (TLC). The reaction
mixturewas purified by filtration through silica gel to givethe
ketone (0.048 g, 97%). 1H NMR (400.13 MHz, CDCl3):
(branimycin numbering) d¼7.35 (1H, H(3), d, J¼10.1),
6.28 (1H, H(4), dd, J¼10.1, 0.3), 5.11 (1H, H(10), d,
J¼10.9), 4.22 (1H, H(7), dd, J¼11.1, 10.3), 4.06 (1H, H(8),
dd, J¼10.3, 4.6), 3.82 (1H, H(11), dd, J¼10.9, 7.7), 3.55 (1H,
H(20), dd, J¼9.6, 4.6), 3.51 (1H, H(20), dd, J¼9.6, 4.1), 3.46
(1H, H(6), dd, J¼11.1, 7.7), 3.33 (3H, CH3O(20), s), 3.15
(3H, CH3O, s), 3.13 (3H, CH3O, s), 2.21 (1H, H(9), ddd,
J¼4.6, 4.6, 4.1), 1.20 (3H, CH3, s), 1.11 (3H, CH3, s); 13C
NMR (100.61 MHz, CDCl3): d¼195.47 (s), 154.18 (s),
133.69 (d), 131.51 (d), 100.44 (s), 100.69 (s), 82.32 (d),
68.60 (t), 66.20 (d), 65.35 (d), 59.02 (q), 47.79 (q), 47.66
(q), 45.36 (d), 44.94 (d), 43.64 (d), 17.57 (q), 17.56 (q); IR
(Si, film) nmax¼2930, 1717, 1420, 1115, 1064, 947 cmꢀ1
;
MS (EI, 70 eV) m/e (relative intensity): 367 (M+, 25), 336
(12), 280 (27), 236 (33), 219 (31), 174 (100), 158 (29), 129
(33), 101 (82); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C18H25O7N (M+): 367.1631, found: 369.1638.
3.1.13. Compound 15. To a slurry of NaH (0.016 g, 60%,
0.41 mmol) in THF/DMF, 1:1 (8 mL) was added at 0 ꢁC a
solution of 11 (0.1 g, 0.27 mmol) in THF (1.5 mL) and the
mixture was stirred for 1 h. Then BnBr (0.06 mL, 2 equiv)
A mixture of the ketone (0.48 g, 1.30 mmol), CeCl3$7H2O
(0.06 g) and NaBH4 (0.06 g) was stirred in MeOH (19 mL)

V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
5937
was added and the mixture was stirred for 16 h at room tem-
perature. The reaction was quenched with saturated
NaHCO3 solution. The mixture was diluted with toluene
(10 mL) and H2O (5 mL), the organic layer was separated
and the aqueous phase was extracted with toluene
(2ꢂ5 mL). The combined organic layers were washed with
brine and the solvent was removed under reduced pressure
and the residue was purified by flash chromatography on sil-
CDCl3): (branimycin numbering) d¼7.25 (2H, H(ar), d,
J¼8.7), 6.89 (2H, H(ar), d, J¼8.7), 4.96 (1H, H(10), dd,
J¼12.0, 1.0), 4.65 (1H, H(3), dd, J¼11.0, 4.0), 4.60 (2H,
CH2O(ar), s), 4.26 (1H, H(5), dd, J¼3.0, 2.7), 4.12 (1H,
H(4), ddd, J¼10.2, 4.0, 2.7), 4.02 (1H, H(7), dd, J¼11.3,
10.8), 3.83 (1H, OH(3), d, J¼11.0), 3.81 (3H, CH3O(ar),
s), 3.74 (1H, H(11), dd, J¼12.0, 8.4), 3.67 (1H, H(8), dd,
J¼10.8, 4.3), 3.49 (1H, H(20), dd, J¼9.7, 4.3), 3.46 (1H,
H(20), dd, J¼9.7, 5.1), 3.31 (3H, CH3O(20), s), 3.16 (3H,
CH3O(7), s), 3.11 (3H, CH3O(8), s), 2.91 (1H, H(6), ddd,
J¼11.3, 8.4, 3.0), 2.91 (1H, OH(4), d, J¼10.2), 2.11 (1H,
H(9), dddd, J¼5.1, 4.3, 4.3, 1.0), 1.20 (3H, CH3, s), 1.195
(3H, CH3, s); 13C NMR (100.61 MHz, CDCl3): d¼159.77
(s), 158.30 (s), 129.75 (2ꢂd), 128.99 (s), 114.11 (2ꢂd),
100.25 (s), 99.73 (s), 80.38 (d), 80.05 (d), 73.79 (t), 70.12
(d), 68.61 (t), 67.43 (d), 65.62 (d), 64.76 (d), 58.91 (q),
55.29 (q), 47.68 (q), 47.66 (q), 43.76 (d), 39.83 (d), 34.57
(d), 17.67 (q), 17.55 (q); IR (Si, film) nmax¼3456, 2946,
1612, 1514, 1377, 1251, 1115, 1075, 847 cmꢀ1; MS (EI,
70 eV) m/e (relative intensity): 491 (M+ꢀCH3OH, 4), 375
(3), 239 (3), 121 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C25H33NO9 (M+ꢀCH3OH): 491.2155, found: 491.2164.
1
ica gel to give 15 (0.11 g, 87%). H NMR (400.13 MHz,
CDCl3): (branimycin numbering) d¼7.40–7.27 (5H, H(ar),
m), 6.62 (1H, H(3), d, J¼10.0), 6.42 (1H, H(4), dd,
J¼10.0, 5.2), 4.98 (1H, H(10), d, J¼10.7), 4.64 (1H,
OCH2(ar), d, J¼11.6), 4.59 (1H, OCH2(ar), d, J¼11.6),
4.43 (1H, H(5), dd, J¼5.2, 1.7), 4.04 (1H, H(7), dd,
J¼10.7, 10.4), 3.89 (1H, H(8), dd, J¼10.4, 4.7), 3.76 (1H,
H(11), dd, J¼10.7, 6.7), 3.53 (1H, H(20), dd, J¼9.5, 3.9),
3.43 (1H, H(20), dd, J¼9.5, 6.7), 3.33 (3H, CH3O(20), s),
3.13 (3H, CH3O(7), s), 3.09 (3H, CH3O(8), s), 2.99 (1H,
H(6), ddd, J¼10.7, 6.7, 1.7), 2.14 (1H, H(9), m), 1.18 (3H,
CH3, s), 1.12 (3H, CH3, s); 13C NMR (100.61 MHz,
CDCl3): d¼155.64 (s), 138.24 (s), 135.34 (d), 128.47
(2ꢂd), 127.84 (d), 127.76 (2ꢂd), 119.73 (d), 100.33 (s),
99.90 (s), 80.30 (d), 71.26 (t), 69.41 (d), 68.70 (t), 65.98
(d), 65.19 (d), 58.92 (q), 47.57 (q), 47.52 (q), 44.11 (d),
42.48 (d), 35.19 (d), 17.65 (q), 17.63 (q).
3.1.16. Compound 18. A solution of 17 (0.177 g,
0.338 mmol), 2,2-dimethoxypropane (26 mL) and a catalytic
amount of PPTS was stirred in DMF (5 mL) at room temper-
ature for 48 h until the staring material was consumed. After
the addition of pyridine (0.2 mL) water (30 mL) was added
the mixture was extracted with EtOAc (3ꢂ50 mL). After
drying (MgSO4), the solvent was removed under reduced
pressure and the residue was purified by flash chromato-
graphy on silica gel to give 18 (0.185 g, 97%), white crystals,
3.1.14. Compound 16. A mixture of 15 (0.050 g, 0.1 mmol)
and Mo(CO)6 (0.014 g, 0.11 mmol) in CH3CN (5 mL, 5
drops H2O) was refluxed for 2 h. The reaction was cooled
to room temperature and the solvent removed in vacuo.
The residue was filtered through silica gel to give 16
(0.042 g, 82%). 1H NMR (600.13 MHz, CDCl3): (branimy-
cin numbering) d¼7.41–7.27 (5H, H(ar), m), 4.63 (1H,
OCH2(ar), d, J¼12.1), 4.47 (1H, OCH2(ar), d, J¼12.1),
4.34 (1H, H(10), m), 4.25 (1H, H(4), ddd, J¼6.3, 3.5, 1.8),
4.19 (1H, H(8), dd, J¼10.6, 6.6), 4.18 (1H, H(5), d,
J¼6.3), 3.75 (1H, H(7), dd, J¼10.6, 4.6), 3.62 (1H, H(20),
dd, J¼10.0, 4.1), 3.33 (1H, H(20), dd, J¼10.4, 10.0), 3.28
(3H, CH3O(20), s), 3.24 (3H, CH3O(7), s), 3.23 (3H,
CH3O(8), s), 2.78 (1H, H(3), dd, J¼19.2, 1.9), 2.65 (1H,
H(11), dd, J¼3.2, 1.2), 2.53 (1H, H(3), ddd, J¼19.2, 3.5,
1.1), 2.41 (1H, H(9), dddd, J¼10.4, 6.6, 4.1, 3.2), 2.32
(1H, H(6), m), 1.33 (3H, CH3, s), 1.28 (3H, CH3, s); 13C
NMR (100.61 MHz, CDCl3) d¼210.39 (s), 138.20 (s),
128.28 (2ꢂd), 127.99 (2ꢂd), 127.60 (d), 100.19 (s),
100.07 (s), 71.48 (d), 70.78 (d), 69.83 (d), 69.79 (t), 67.73
(t), 66.37 (d), 65.12 (d), 59.04 (q), 47.95 (q), 47.83 (q),
46.34 (d), 42.28 (d), 42.17 (d), 39.46 (t), 17.87 (q), 17.74
(q); IR (Si, film) nmax¼2923, 2853, 1737, 1651, 1455,
1376, 1198, 1118, 885 cmꢀ1; MS (EI, 70 eV) m/e (relative
intensity): 462 (M+, 0.8), 447 (2.5), 431 (6), 314 (15), 223
(10), 156 (18), 91 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd
for C25H34O8 (M+): 462.2254, found: 462.2244.
1
mp¼87.0–87.7 ꢁC (from hexane). H NMR (400.13 MHz,
CDCl3): (branimycin numbering) d¼7.31 (2H, H(ar), d,
J¼8.7), 6.85 (2H, H(ar), d, J¼8.7), 4.83 (1H, H(3), d,
J¼7.2), 4.71 (1H, H(10), dd, J¼11.4, 3.9), 4.67 (1H,
OCH2(ar), d, J¼11.5), 4.56 (1H, OCH2(ar), d, J¼11.5),
4.51 (1H, H(4), dd, J¼7.2, 2.5), 4.10 (1H, H(7), dd,
J¼11.0, 8.6), 3.90 (1H, H(8), dd, J¼11.0, 5.5), 3.797 (3H,
CH3O(ar), s), 3.795 (1H, H(11), dd, J¼11.4, 10.7), 3.64
(1H, H(5), dd, J¼10.4, 2.5), 3.32 (3H, CH3O(20), s), 3.24
(3H, CH3O(8), s), 3.18 (3H, CH3O(7), s), 2.96 (1H, H(6),
ddd. J¼10.7, 10.4, 8.6), 2.28 (1H, H(9), dddd, J¼5.5, 5.2,
4.8, 3.9), 1.54 and 1.34 (2ꢂ3H, C(CH3)2, s), 1.27 (6H,
2ꢂCH3, s); 13C NMR (100.61 MHz, CDCl3): d¼159.13
(s), 156.56 (s), 130.88 (s), 129.30 (2ꢂd), 113.66 (2ꢂd),
110.50 (s), 100.10 (s), 99.55 (s), 81.23 (d), 75.96 (d),
74.25 (d), 71.68 (t), 68.69 (t), 68.66 (d), 65.72 (d), 65.01
(d), 58.74 (q), 55.27 (q), 47.78 (q), 47.76 (q), 42.61 (d),
40.53 (d), 35.95 (d), 26.62 (q), 24.39 (q), 17.87 (q), 17.69
(q); IR (Si, film) nmax¼2936, 1612, 1514, 1459, 1375,
1211, 1124, 896 cmꢀ1; MS (EI, 70 eV) m/e (relative inten-
sity): 531 (M+ꢀCH3OH, 2.5), 311 (12), 244 (7), 163 (8),
134 (30), 121 (100); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C28H37NO9 (M+ꢀCH3OH): 531.2468, found: 531.2456.
3.1.15. Compound 17. A solution of OsO4 (0.04 g) in pyri-
dine (0.8 mL) was added dropwise at ꢀ25 ꢁC to a solution
of 10 (0.04 g, 0.082 mmol) in pyridine (1 mL). After stirring
for 1 h at ꢀ25 ꢁC and 1 h at room temperature THF (4 mL),
FlorisilÒ (3.2 g) and Na2S2O5 (1.28 g) were added. After
24 h the residue was diluted with EtOAc (10 mL), filtered
through silica gel, and the solvent was removed under
reduced pressure to give 17 (0.037 g, 86%), white crystals,
mp¼119.3–120.1 ꢁC (from hexane). 1H NMR (400.13 MHz,
3.1.17. Compound 19. Raney-nickel (0.02 g, 50% in water),
boronic acid (0.050 g) and 18 (0.05 g, 0.0888 mmol) were
stirred in MeOH/H2O, 10:1 (4.4 mL) at room temperature
under hydrogen atmosphere for 4 h. The reaction mixture
was filtered through a Celite path and the filtrate was washed
with saturated aqueous NaHCO3, dried (MgSO4) and con-
centrated in vacuo to provide 19 (0.045 g, 90%) after

5938
V. S. Enev et al. / Tetrahedron 63 (2007) 5930–5939
1
chromatography. H NMR (400.13 MHz, CDCl3): (brani-
mycin numbering) d¼7.36 (2H, H(ar), d, J¼8.6), 6.88
(2H, H(ar), d, J¼8.6), 4.86 (1H, OCH2(ar), d, J¼12.6),
4.75 (1H, OCH2(ar), d, J¼12.6), 4.65 (1H, H(5), dd,
J¼11.5, 3.6), 4.44 (1H, H(8), dd, J¼11.5, 5.9), 4.242 (1H,
H(3), d, J¼4.8), 4.239 (1H, H(10), m), 4.13 (1H, H(4), dd,
J¼4.8, 3.6), 3.81 (3H, CH3O(ar), s), 3.766 (1H, H(20), dd,
J¼9.6, 3.3), 3.762 (1H, H(7), dd, J¼11.5, 5.0), 3.36 (3H,
CH3O(8), s), 3.32 (3H, CH3O(20), s), 3.26 (1H, H(20), dd,
J¼10.0, 9.6), 3.21 (3H, CH3O(7), s), 2.94 (1H, H(6), ddd,
J¼11.5, 5.7, 5.0), 2.79 (1H, H(11), m), 2.25 (1H, H(9), m),
1.73 (1H, OH, dd, J¼3.8, 1.8), 1.38 and 1.33 (2ꢂ3H,
C(CH3)2, s), 1.31 (3H, CH3, s), 1.30 (3H, CH3, s); 13C
NMR (100.61 MHz, CDCl3): d¼209.86 (s), 159.10 (s),
131.82 (s), 129.62 (2ꢂd), 113.61 (2ꢂd), 109.36 (s), 99.41
(s), 99.19 (s), 79.02 (d), 78.56 (d), 73.28 (t), 72.49 (d),
70.44 (d), 68.58 (t), 67.07 (d), 63.47 (d), 59.04 (q), 55.25
(q), 50.96 (d), 47.98 (q), 47.91 (q), 37.80 (d), 27.25 (q),
25.79 (q), 17.73 (q), 17.66 (q); IR (Si, film) nmax¼3606,
2924, 1727, 1681, 1651, 1557, 1455, 1373, 1123,
807 cmꢀ1; MS (EI, 70 eV) m/e (relative intensity): 534
(M+ꢀCH3OH, 5), 516 (3), 282 (2), 205 (2.5), 138 (7), 121
(100); HRMS (EI, 70 eV, 60 ꢁC) calcd for C28H38O10
(M+ꢀCH3OH): 534.2465, found: 534.2457.
brine and the solvent was removed under reduced pressure
and the residue was purified by flash chromatography on sil-
ica gel to give 21 (0.047 g, 72%). H NMR (600.13 MHz,
1
CDCl3): (branimycin numbering) d¼7.39 (2H, H(ar), d,
J¼8.5), 6.86 (2H, H(ar), d, J¼8.5), 5.79 (1H, H(13), dd,
J¼17.2, 10.7), 5.40 (1H, H(14), dd, J¼17.2, 1.4), 5.22 (1H,
H(14), dd, J¼10.7, 1.4), 4.76 (1H, OCH2(ar), d, J¼12.7),
4.74 (1H, OCH2(ar), d, J¼12.7), 4.41 (1H, H(5), dd, J¼11.7,
5.7), 4.29 (1H, H(8), dd, J¼11.3, 6.0), 4.17 (1H, H(10),
dd, J¼2.3, 1.9), 4.02 (1H, H(3), d, J¼6.5), 3.88 (1H, H(4),
dd, J¼6.5, 4.7), 3.80 (3H, CH3O(ar), s), 3.76 (1H, H(7), dd,
J¼11.3, 5.3), 3.73 (1H, H(20), dd, J¼9.9, 3.6), 3.35 (3H,
CH3O(8), s), 3.28 (3H, CH3O(20), s), 3.21 (3H, CH3O(7),
s), 3.20 (1H, H(20), dd, J¼10.2, 9.9), 2.91 (1H, H(6), ddd,
11.7, 5.3, 4.4), 2.74 (1H, OH, s), 2.24 (1H, H(9), m), 2.02
(1H, H(11), dd, J¼4.4, 2.3), 1.56 and 1.28 (2ꢂ3H, C(CH3)2,
s), 1.30 (3H, CH3, s), 1.29 (3H, CH3, s), 0.05 (9H, Si(CH3)3,
s); 13C NMR (chemical shifts from 2D HSQC and HMBC
spectra) (150.90 MHz, CDCl3): d¼159.0 (s), 141.7 (d), 132.0
(s), 129.5 (2ꢂd), 114.8 (t), 113.3 (2ꢂd), 108.3 (s), 99.1 (s),
98.9 (s), 81.0 (s), 77.2 (d), 74.9 (d), 72.5 (t), 71.8 (d), 70.2
(d), 69.2 (t), 68.2 (d), 64.2 (d), 59.0 (q), 55.3 (q), 48.2 (d),
48.0 (q), 47.8 (q), 46.1 (d), 34.8 (d), 26.5 (q), 24.5 (q), 17.8
(2ꢂq), 0.05 (3ꢂq); HRMS (EI, 70 eV, 60 ꢁC) calcd for
C34H54O11Si (M+): 666.3435, found: 666.33423.
3.1.18. Compound 20. To a solution of 19 (0.05 g,
0.9 mmol) in DCM (5 mL), 2,6-lutidine (0.31 mL,
2.6 mmol) was added, and the mixture was cooled toꢀ78 ꢁC.
TMSOTf (0.32 mL, 1.41 mmol) was added dropwise over
15 min and the reaction mixture was stirred for additional
30 min atꢀ78 ꢁC. Then it was warmed to room temperature
and after 1.5 h quenched with saturated NaHCO3 solution.
The mixture was diluted with toluene (10 mL) and H2O
(5 mL), the organic layer was separated and the aqueous
phase was extracted with toluene (2ꢂ5 mL). The combined
organic layers werewashed with brine and the solvent was re-
moved under reduced pressure to give the residue that was
purified by flash chromatography on silica gel to give 20
(0.03 g, 56%). 1H NMR (250.13 MHz, CDCl3): (branimycin
numbering) d¼7.36 (2H, H(ar), d, J¼8.5), 6.88 (2H, H(ar), d,
J¼8.5), 4.79 (2H, OCH2(ar), s), 4.68 (1H, H(5), dd, J¼11.5,
3.2), 4.40 (1H, H(8), dd, J¼11.6, 5.8), 4.21 (1H, H(10), dd,
J¼4.4, 4.4), 3.91 (2H, H(3,4), m), 3.81 (3H, CH3O(ar), s),
3.75 (1H, H(7), dd, J¼11.6, 5.3), 3.73 (1H, H(20), dd,
J¼10.0, 3.3), 3.36 (3H, CH3O(20), s), 3.30 (3H, CH3O(8),
s), 3.23 (1H, H(20), dd, J¼10.0, 9.4), 3.21 (3H, CH3O(7),
s), 2.92 (1H, H(6), ddd, 10.7, 5.3, 5.3), 2.77 (1H, H(11), dd,
J¼5.1, 2.9), 2.28 (1H, H(9), m), 1.36 (6H, C(CH3)2, s),
1.30 (6H, 2ꢂCH3, s), 0.05 (9H, Si(CH3)3, s); IR (Si, film)
nmax¼2924, 1727, 1681, 1651, 1557, 1455, 1373, 1123,
807 cmꢀ1; MS (EI, 70 eV) m/e (relative intensity): 534
(M+ꢀCH3OH, 5), 516 (3), 282 (2), 205 (2.5), 138 (7), 121
(100): HRMS (EI, 70 eV, 60 ꢁC) calcd for C32H50O11Si
(M+): 638.3122, found: 638.3118.
References and notes
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