Total synthesis of pamamycin-649B

Article abstract of DOI:10.1002/chem.201102093

The first total synthesis of the macrodiolide antibiotic pamamycin-649B (1) was achieved by using sultone methodology. The diethyl substituted larger hydroxy acid fragment was constructed in a concise fashion through domino elimination/alkoxide-directed 1

Full text of DOI:10.1002/chem.201102093

DOI: 10.1002/chem.201102093
Total Synthesis of Pamamycin-649B
Petra Fischer, Margit Gruner, Anne Jꢀger, Olga Kataeva, and Peter Metz*[a]
Dedicated to Professor Barry M. Trost on the occasion of his 70th birthday
Abstract: The first total synthesis of
the macrodiolide antibiotic pamamy-
cin-649B (1) was achieved by using sul-
tone methodology. The diethyl substi-
tuted larger hydroxy acid fragment was
lar Diels–Alder reaction of furan-con-
taining vinylsulfonates. Intermolecular
Yamaguchi esterification of the two hy-
droxy acid building blocks and subse-
quent Yamaguchi cyclization eventually
provided the target macrocycle 1. Since
the final lactonization with formation
of the ester linkage between C1’ and
the C8 oxygen proceeded with com-
plete C2’ epimerization, the more read-
ily available C2’ epimeric smaller frag-
ment could be used to streamline the
synthetic sequence.
constructed in
a
concise fashion
Keywords: antibiotics
reactions natural products
sulfur heterocycles · total synthesis
·
domino
through domino elimination/alkoxide-
directed 1,6-additions of ethyllithium
to sultones derived from intramolecu-
·
·
Introduction
the antimycobacterial activity of pamamycin-607 (1a) on 25
independent M. tuberculosis clinical isolates (either suscepti-
ble, mono-, or multiresistant to the first line antituberculous
drugs) established minimum inhibitory concentrations
MIC100 in the range of 1.5–2.0 mgmLꢀ1, while the MIC100 of
1a for a bioluminescent laboratory strain of M. tuberculosis
(H37Rv) was determined as 0.55 mgmLꢀ1.[2a] Parallel studies
on the effect of 1a on the cell cycle distribution of human
(HL-60) cells by flow cytometry indicated no (cell cycle) or
only small effects (apoptosis) at the latter concentration.[2b]
Thus, 1a might emerge as a promising lead molecule for the
development of novel antituberculous drugs.
The pamamycins (1) are structurally intriguing 16-mem-
bered macrodiolides isolated from various Streptomyces spe-
cies that display a wide range of biological activities
(Figure 1).[1] Next to possessing pronounced autoregulatory,
Due to their biological properties and unique structure,
the pamamycin macrodiolides have stimulated considerable
synthetic efforts,[3,4] and the total syntheses of pamamycin-
607 (1a),[5] pamamycin-621A (1b),[6] and pamamycin-635B
(1c) have been achieved.[6a] Our approach to 1a was based
on the extensive application of sultone chemistry.[3a,5c] The
synthetic route developed in this context proved to be quite
general, since modification of the smaller hydroxy acid frag-
ment allowed an efficient access to the homologues 1b and
1c as well.[6a] Here we report the first total synthesis of the
higher homologue pamamycin-649B (1 f)[7] by modification
of the larger hydroxy acid fragment.
Figure 1. Selected pamamycin homologues.
anionophoric, and antifungal activities, several homologues
have been shown to be highly active against Gram-positive
bacteria including multiple antibiotic-resistant strains of My-
cobacterium tuberculosis.[1a] More recent investigations on
Results and Discussion
[a] Dr. P. Fischer, Dr. M. Gruner, A. Jꢀger, Dr. O. Kataeva,+
Prof. Dr. P. Metz
Retrosynthetic disconnection of 1 f led to the silylated larger
hydroxy acid 2 that also occurs in pamamycin-635F (1d)
and -649A (1e) as well as to the benzyl ester 3 or its C2’
epimer 4 (Scheme 1). Since the more readily available C2’
epimeric smaller fragment 4 had previously been used suc-
cessfully in a streamlined total synthesis of pamamycin-
621A (1b),[6a] we felt that it could also be applied to a corre-
sponding shortened access to pamamycin-649B (1 f).
Fachrichtung Chemie und Lebensmittelchemie, Organische Chemie I
Technische Universitꢀt Dresden, Bergstrasse 66
01069 Dresden (Germany)
Fax : (+49)351-463-33162
E-mail: peter.metz@chemie.tu-dresden.de
[+] X-ray diffraction analysis.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102093.
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Chem. Eur. J. 2011, 17, 13334 – 13340

FULL PAPER
equivalents of ethyllithium afforded the cyclohexene 17.
Ozonolysis of 17 with eliminative workup at elevated tem-
perature and treatment of the intermediate hemiacetal 18
with thiophenol in the presence of trifluoroborane not only
effected lactol S,O-acetal interchange, but simultaneously
cleaved the silyl ether on the side chain to give alcohol 19
with complete diastereoselectivity. Subjecting 19 to a Mitsu-
nobu reaction with hydrazoic acid delivered azide 20 nearly
quantitatively. Subsequent treatment of 20 with Raney
nickel under hydrogen pressure followed by addition of an
aqueous formaldehyde solution to the reaction mixture
caused desulfurization via domino reductive elimination/hy-
drogenation, azide reduction, and twofold reductive N-
methylation to provide alcohol 21.[12] Silylation of 21 then
yielded TBS ether 22 as a single stereoisomer.
Mild saponification of methyl ester 22 yielded the larger
fragment coupling component 2 (Scheme 4). The total syn-
thesis of 1 f was then completed using the C2’ epimeric
smaller fragment benzyl ester 4. Intermolecular Yamaguchi
esterification[13] of 2 with 4 at reflux in toluene efficiently
provided coupling product 23. Desilylation of 23 and reduc-
tive debenzylation of the resulting benzyl ester 24 proceed-
ed uneventfully to give seco-acid 25. Finally, modified Ya-
maguchi cyclization of 25 (0.7ꢂ10ꢀ3 m) under Fleming condi-
tions[14] afforded pamamycin-649B (1 f) as the single macro-
diolide product in good yield.[15] Thus, as has been observed
during the total syntheses of the homologues 1a–c,[3a,6a] the
final Yamaguchi lactonization with formation of the ester
linkage between C1’ and the C8 oxygen proceeded with
complete C2’ epimerization.
Scheme 1. Retrosynthetic analysis of 1 f. TBS=tert-butyldimethylsilyl.
Sultone 5 that already served as a building block for the
pamamycins 1a–c,[3a,5c,6a] was treated with two equivalents of
ethyllithium, which induced a domino elimination/alkoxide-
directed 1,6-addition to yield the bicyclic compound 6
(Scheme 2). Ozonolysis of this cyclohexene followed by
eliminative workup at reflux in dichloromethane afforded a
single hemiacetal 7. Lewis-acid-catalyzed exchange of the
hydroxyl group in 7 against a phenylthio group in 8 proceed-
ed with retention of configuration as proven by X-ray dif-
fraction analysis.[8] Subjecting thioether 8 to a domino reduc-
tive elimination/hydrogenation with Raney nickel under hy-
drogen pressure gave alcohol 9.[6a,9] Silylation followed by
ester reduction and iodide substitution then delivered the
iodide 12. Halogen–lithium exchange of 12, addition of the
resultant organolithium intermediate to 2-acetylfuran (13),
and brief exposure of the alcohols thus formed to catalytic
amounts of concentrated aqueous hydrogen chloride
smoothly yielded the (E)-olefin 14. Diastereoselective hy-
droboration/oxidation of 14 gave largely the desired stereo-
isomer 15 due to minimization of allylic 1,3-strain.[10,11]
The second iterative cycle of our sultone route com-
menced with a domino esterification/cycloaddition by react-
ing hydroxyalkylfuran 15 with vinylsulfonyl chloride
(Scheme 3).[10] The resultant single sultone 16 gave suitable
crystals for X-ray diffraction analysis.[8] Domino elimination/
alkoxide-directed 1,6-addition by treatment of 16 with two
Conclusion
In conclusion, a short and highly stereoselective access to
the silylated larger hydroxy acid 2 of the pamamycins 1d–f
has been developed by application of sultone methodology.
Subsequent coupling of 2 with the smaller fragment surro-
Scheme 2. Sultone route to hydroxy ester 9 and its elaboration to hydroxyalkylfuran 15. a) 1) 2 equiv EtLi, THF, Et2O, hexane, ꢀ788C ! RT, 2) NH4Cl,
H2O, 36%; b) 1) O3, NaHCO3, CH2Cl2, MeOH, ꢀ788C, 2) Ac2O, pyridine, CH2Cl2, RT ! reflux, 87%; c) PhSH, BF3·Et2O, CH2Cl2, 08C ! RT, 78 %;
d) Raney Ni (W2), 50 bar H2, EtOH, RT, 45%; e) TBSCl, imidazole, DMAP, DMF, RT, 98%; f) LiAlH4, Et2O, 0 8C ! RT, 97 %; g) I2, Ph3P, imidazole,
Et2O, MeCN, RT, 99%; h) 1) tBuLi, Et2O, hexane, ꢀ788C, 2) 13, MS 4 ꢃ, ꢀ788C ! RT; i) conc. aq. HCl, CH2Cl2, RT, 71% from 12; j) 1) BH3·THF,
THF, 08C ! RT, 2) 30% aq. H2O2, NaOH, 08C ! RT, 51%. DMAP=4-(N,N-dimethylamino)pyridine, MS=molecular sieves.
Chem. Eur. J. 2011, 17, 13334 – 13340
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13335

P. Metz et al.
Scheme 3. Sultone route to the protected larger fragment 22. a) CH2=CHSO2Cl, Et3N, THF, 08C ! RT, 88%; b) 1) 2 equiv EtLi, THF, Et2O, hexane,
ꢀ788C ! RT, 2) NH4Cl, H2O, 58%; c) 1) O3, NaHCO3, CH2Cl2, MeOH, ꢀ788C, 2) Ac2O, pyridine, CH2Cl2, 08C ! reflux, 78%; d) PhSH, BF3·Et2O,
CH2Cl2, 08C ! RT, 76 %; e) HN3, DIAD, Ph3P, toluene, 08C ! RT, 98%; f) 1) Raney Ni (W2), 50 bar H2, EtOH, RT, 2) 37% aq. CH2O, 50 bar H2, RT;
g) TBSOTf, 2,6-lutidine, CH2Cl2, 08C ! RT, 47% from 20. DIAD=diisopropyl azodicarboxylate.
Scheme 4. Final steps of the synthesis of pamamycin-649B (1 f). a) LiOH, THF, MeOH, RT, 41% (77% based on recovered starting material);
b) 1) 2,4,6-trichlorobenzoyl chloride, Et3N, THF, RT, 2) 4, DMAP, toluene, reflux, 80%; c) 40% aq. HF, MeCN, RT, 91%; d) H2, 10% Pd/C, THF, RT;
e) 2,4,6-trichlorobenzoyl chloride, DMAP, MS 4 ꢃ, CH2Cl2, RT, 53% from 24.
solvent or TMS. FT-IR: Nicolet Avatar 360 spectrometer. Mass spectra:
Agilent 5973N detector coupled with an Agilent 6890N GC (GC/MS,
70 eV) or else Bruker Esquire-LC (direct injection as a methanolic
NH4OAc solution, ESI). Exact mass: Finnigan MAT 95. Elemental analy-
gate 4 enabled the first total synthesis of pamamycin-649B
(1 f). Further biological evaluation of the pamamycins is on-
going and will be reported in due course.
sis: Hekatech EA 3000. X-Ray: Bruker Kappa CCD diffractometer.
Cyclohexene 6: To generate EtLi, freshly distilled EtI (0.50 mL,
6.19 mmol) was dissolved in Et2O (15 mL) and tBuLi (1.5m solution in
Experimental Section
hexane, 8.60 mL, 12.9 mmol) was added to this solution at ꢀ788C. After
stirring for 1 h at this temperature and additional 2 h at room tempera-
ture, the resulting suspension was added dropwise to a solution of 5
(500 mg, 2.05 mmol) in THF (55 mL) at ꢀ788C. The reaction mixture
was stirred for 30 min at ꢀ788C and then for 1 h at room temperature.
Subsequently, it was quenched with saturated aqueous NH4Cl solution
(10 mL), and the aqueous layer was extracted with Et2O (4ꢂ10 mL). The
combined organic layers were dried and filtered. After removal of the
solvent and purification by flash chromatography (CH2Cl2/Et2O 6:1), cy-
clohexene 6 (215 mg, 36%) was isolated as a white solid. Rf =0.35
(CH2Cl2/Et2O 6:1); m.p. 478C; [a]2D5 =ꢀ34.9 (c=0.90 in CH2Cl2);
1H NMR (500 MHz, CDCl3): d=0.91–0.94 (m, 6H), 1.26–1.34 (m, 1H),
General: All reactions requiring exclusion of moisture were run under
argon using flame-dried glassware. Solvents were dried by distillation
from Na/K and benzophenone (THF), Na (toluene) or CaH2 (CH2Cl2).
All commercially available compounds were used as received unless
stated otherwise. MgSO4 was generally utilized for drying after extractive
work-up. Flash chromatography: Merck silica gel 60 (40–63 mm). Thin-
layer chromatography: Merck silica gel 60 F254 plates. Melting points:
Kleinfeld Labortechnik Electrothermal IA 9100 apparatus. Optical rota-
1
tion: Perkin–Elmer 341 polarimeter. H and 13C NMR: Bruker DRX-500
(1H: 500 MHz, 13C: 126 MHz), calibrated to the residual resonance of the
13336
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Chem. Eur. J. 2011, 17, 13334 – 13340

Total Synthesis of Pamamycin-649B
FULL PAPER
1.38–1.61 (m, 3H), 1.65–1.77 (m, 2H), 2.09–2.18 (m, 2H), 2.30–2.35 (m,
2H), 2.39–2.45 (m, 2H), 3.52–3.58 (m, 1H), 3.82–3.85 (m, 1H), 4.52–4.57
(m, 1H), 5.71–5.72 ppm (m, 1H); 13C NMR (126 MHz, CDCl3): d=10.68
(q), 13.53 (q), 17.93 (t), 24.44 (t), 28.85 (t), 36.73 (t), 38.74 (t), 44.47 (d),
59.25 (d), 68.10 (d), 84.76 (d), 126.20 (s), 131.96 ppm (d); IR (KBr): n=
3224 (broad), 2960, 2934, 2874, 1459, 1432, 1352, 1337, 1289, 1216, 1199,
1166, 1137, 1118, 1069, 1015, 961, 936, 893, 880, 819, 802, 785, 734, 682,
619 cmꢀ1; MS (GC/MS, 70 eV): m/z (%): 166 (100) [MꢀCH3CHOꢀSO2]+;
elemental analysis calcd (%) for C13H22O4S: C 56.91, H 8.08, S 11.69;
found: C 57.03, H 8.12, S 11.50.
13C NMR (126 MHz, CDCl3): d=11.84 (q), 14.07 (q), 18.94 (t), 22.36 (t),
29.45 (t), 30.39 (t), 39.32 (t), 40.95 (t), 51.50 (q), 53.69 (d), 68.66 (d),
76.75 (d), 80.54 (d), 174.77 ppm (s); IR (neat): n=3449 (broad), 2957,
2935, 2873, 1736, 1460, 1435, 1378, 1348, 1270, 1238, 1196, 1176, 1160,
1076, 1025, 997, 905, 846, 798, 748, 671, 621, 577, 552 cmꢀ1; MS (ESI):
m/z: 241.3 [MꢀH2O+H]+, 259.2 [M+H]+, 276.2 [M+NH4]+; elemental
analysis calcd (%) for C14H26O4: C 65.09, H 10.14; found: C 64.90, H
10.36.
Silylether 10: Imidazole (671 mg, 9.86 mmol), DMAP (482 mg,
3.95 mmol) and TBSCl (1.19 g, 7.89 mmol) were added to a solution of 9
(1.02 g, 3.95 mmol) in DMF (30 mL). After stirring for 3 h at room tem-
perature, the reaction was quenched with water (50 mL), and Et2O
(40 mL) was added. The aqueous layer was extracted with Et2O (3ꢂ
50 mL), and then the combined organic layers were washed with 2n HCl
(50 mL) and saturated aqueous NaHCO3 solution (50 mL), dried and fil-
tered. Purification by flash chromatography (pentane/Et2O 5:1) gave 10
(1.44 g, 98%) as a colorless liquid. Rf =0.48 (pentane/Et2O 5:1); [a]2D5 = +
19.1 (c=1.44 in CH2Cl2); 1H NMR (300 MHz, CDCl3): d=0.01 (s, 6H),
0.08–0.90 (m, 15H), 1.27–1.33 (m, 2H), 1.37–1.60 (m, 8H), 1.91–1.95 (m,
2H), 2.25–2.30 (m, 1H), 3.67 (s, 3H), 3.68–3.80 (m, 1H), 3.85–3.90 ppm
(m, 2H); 13C NMR (75.5 MHz, CDCl3): d=ꢀ4.76 (q), ꢀ4.58 (q), 11.91
(q), 14.34 (q), 17.98 (t), 18.10 (s), 22.27 (t), 25.94 (q), 29.40 (t), 31.33 (t),
40.49 (t), 43.42 (t), 51.32 (q), 54.07 (d), 69.53 (d), 75.91 (d), 79.84 (d),
174.78 ppm (s); IR (neat): n=2955, 2934, 2857, 1740, 1462, 1434, 1380,
Hemiacetal 7: Cyclohexene 6 (3.71 g, 12.9 mmol) was dissolved in CH2Cl2
(80 mL) and MeOH (25 mL), and NaHCO3 (3.66 g, 43.6 mmol) were
added. This suspension was ozonized at ꢀ788C until a constant blue colo-
ration was reached. To remove excessive ozone, the reaction mixture was
purged with N2. Subsequently, the mixture was allowed to reach room
temperature. NaHCO3 was filtered off, and the solvent was evaporated at
308C. The residue was at first dissolved in THF (10 mL) and after evapo-
ration of the solvent dissolved again in CH2Cl2 (30 mL). Pyridine
(2.08 mL, 25.7 mmol) and Ac2O (1.22 mL, 12.9 mmol) were added, and
the resulting solution was stirred for 12 h at room temerature and further
12 h under reflux. Thereafter it was diluted with Et2O (200 mL) and
washed with 1n HCl (75 mL) and saturated aqueous NaHCO3 solution
(75 mL). The organic layer was then dried and the solvent removed at
308C. Final purification by flash chromatography (pentane/EtOAc 3:1)
gave 7 (3.78 g, 87%) as a colorless oil. Rf =0.39 (pentane/EtOAc 1:1);
1252, 1195, 1177, 1154, 1076, 1038, 1005, 946, 920, 834, 808, 774, 663 cmꢀ1
;
MS (ESI): m/z: 373.1 [M+H]+; elemental analysis calcd (%) for
1
[a]2D5 =ꢀ28.6 (c=1.15 in CH2Cl2); H NMR (500 MHz, CDCl3): d=0.91–
C20H40O4Si: C 64.47, H 10.82; found: C 64.68, H 10.92.
0.96 (m, 6H), 1.37–1.43 (m, 1H), 1.51–1.60 (m, 3H), 1.66–1.74 (m, 2H),
2.04–2.07 (m, 1H), 2.21 (m, 1H), 2.36–2.41 (m, 1H), 2.48–2.53 (m, 1H),
2.65–2.69 (m, 1H), 3.61 (d, J=7.3 Hz, 1H), 3.72 (s, 3H), 4.34 (s, 1H),
4.57–4.58 (m, 1H), 4.66–4.68 ppm (m, 1H); 13C NMR (126 MHz, CDCl3):
d=11.80 (q), 13.54 (q), 17.97 (t), 22.79 (t), 29.83 (t), 36.22 (t), 39.65 (t),
51.99 (q), 54.06 (d), 65.72 (d), 80.42 (d), 80.49 (d), 104.36 (s), 175.21 ppm
(s); IR (neat): n=3458 (broad), 2963, 2877, 1734, 1710, 1437, 1358, 1257,
1208, 1170, 1096, 1037, 985, 885, 808, 750, 625 cmꢀ1; MS (ESI): m/z: 354.2
[M+NH4]+.
Alcohol 11: To a suspension of LiAlH4 (185 mg, 4.88 mmol) in Et2O
(50 mL) a solution of 10 (1.21 g, 3.25 mmol) in Et2O (25 mL) was added
dropwise at 08C. The reaction mixture was stirred for 1 h at room tem-
perature. Then it was quenched with water (50 mL). The aqueous layer
was extracted with Et2O (3ꢂ50 mL) after addition of 2n HCl (pH 1).
The combined organic layers were washed with saturated aqueous
NaHCO3 solution, dried, filtered, and evaporated. Final purification by
flash chromatography (pentane/Et2O 1:1) afforded 11 (1.09 g, 97%) as a
colorless liquid. Rf =0.51 (pentane/Et2O 1:1); [a]2D5 = +44.5 (c=1.28 in
CHCl3); 1H NMR (300 MHz, CDCl3): d=0.03 (s, 6H), 0.82–0.93 (m,
15H), 1.16–1.23 (m, 1H), 1.26–1.49 (m, 7H), 1.55–1.61 (m, 3H), 1.90–
2.02 (m, 2H), 3.12 (brs, 1H), 3.57–3.61 (m, 1H), 3.66–3.71 (m, 1H), 3.73–
3.79 (m, 2H), 3.90–3.93 ppm (m, 1H); 13C NMR (75.5 MHz, CDCl3): d=
ꢀ4.86 (q), ꢀ4.43 (q), 11.72 (q), 14.30 (q), 17.97 (t), 18.10 (s), 21.64 (t),
25.89 (q), 30.45 (t), 30.97 (t), 40.52 (t), 43.15 (t), 47.29 (d), 65.39 (t), 69.46
(d), 76.34 (d), 84.45 ppm (d); IR (neat): n=3464 (broad), 2956, 2930,
S,O-Acetal 8: To a solution of 7 (2.37 g, 7.05 mmol) in CH2Cl2 (20 mL)
thiophenol (4.68 mL, 45.8 mmol) and BF3·Et2O (1.03 mL, 8.10 mmol)
were added at 08C. After stirring for 1 h at room temperature, the reac-
tion was quenched with saturated aqueous NaHCO3 solution (15 mL).
The aqueous layer was extracted with CH2Cl2 (4ꢂ10 mL), and the com-
bined organic layers were dried and filtered. After evaporation of the sol-
vent, the residue was purified by flash chromatography (pentane/EtOAc
9:1) to afford 8 (2.37 g, 78%) as a colorless oil. Rf =0.16 (pentane/EtOAc
2857, 1463, 1379, 1252, 1039, 1006, 940, 834, 807, 773, 663, 583, 570 cmꢀ1
;
1
9:1); [a]2D5 = +37.3 (c=0.95 in CH2Cl2); H NMR (500 MHz, CDCl3): d=
MS (ESI): m/z: 345.2 [M+H]+; elemental analysis calcd (%) for
0.86 (t, J=7.1 Hz, 3H), 0.95 (t, J=7.4 Hz, 3H), 1.31–1.36 (m, 1H), 1.40–
1.47 (m, 2H), 1.52–1.64 (m, 3H), 2.13–2.15 (m, 2H), 2.59–2.65 (m, 1H),
2.79–2.83 (m, 1H), 2.93–2.98 (m, 1H), 3.77 (s, 3H), 3.82 (d, J=7.1 Hz,
1H), 4.64–4.67 (m, 1H), 4.84–4.89 (m, 1H), 7.33–7.41 (m, 3H), 7.55–
7.57 ppm (m, 2H); 13C NMR (126 MHz, CDCl3): d=11.46 (q), 13.42 (q),
17.85 (t), 22.33 (t), 31.93 (t), 36.16 (t), 39.98 (t), 51.64 (q), 54.59 (d), 65.27
(d), 81.40 (d), 82.70 (d), 95.25 (s), 129.19 (d), 129.65 (d), 130.02 (s),
136.17 (d), 174.09 ppm (s); IR (neat): n=3051, 2875, 1734, 1459, 1439,
1364, 1308, 1269, 1255, 1202, 1167, 1086, 1068, 1022, 985, 929, 889, 832,
807, 751, 692, 620, 553 cmꢀ1; MS (ESI): m/z: 446.0 [M+NH4]+; elemental
analysis calcd (%) for C20H28O6S2: C 56.05, H 6.59, S 14.96; found: C
56.12, H 6.62, S 14.88.
C19H40O3Si: C 66.22, H 11.70; found: C 66.26, H 11.74.
Iodide 12: Alcohol 11 (642 mg, 1.86 mmol) was dissolved in Et2O
(25 mL) and MeCN (10 mL). Imidazole (216 mg, 3.17 mmol), Ph3P
(735 mg, 2.80 mmol) and I2 (709 mg, 2.79 mmol) were added successively.
After stirring for 1 h at room temperature, the reaction was quenched
with water (25 mL), and the aqueous layer was extracted with Et2O (3ꢂ
25 mL). The combined organic layers were washed with saturated aque-
ous Na2S2O3 solution (25 mL), dried and filtered. The filtrate was evapo-
rated, and purification of the residue was achieved by flash chromatogra-
phy (pentane/Et2O 10:1) to give 12 (837 mg, 99%) as a colorless liquid.
Rf =0.66 (pentane/Et2O 10:1); [a]2D5 = +9.4 (c=1.92 in CHCl3); 1H NMR
(500 MHz, CDCl3): d=0.05 (s, 3H), 0.06 (s, 3H), 0.85–0.90 (m, 15H),
0.94–0.95 (m, 1H), 1.26–1.34 (m, 3H), 1.40–1.44 (m, 4H), 1.51–1.54 (m,
3H), 1.93–1.96 (m, 2H), 3.38–3.40 (m, 1H), 3.50–3.51 (m, 1H), 3.54–3.57
(m, 1H), 3.82–3.88 ppm (m, 2H); 13C NMR (75.5 MHz, CDCl3,): d=
ꢀ4.48 (q), ꢀ4.42 (q), 10.59 (q), 13.19 (t), 14.38 (q), 18.01 (t), 18.14 (s),
23.56 (t), 25.98 (q), 29.17 (t), 31.63 (t), 40.53 (t), 43.51 (t), 45.86 (d), 69.57
(d), 75.53 (d), 80.56 ppm (d); IR (neat): n=2956, 2930, 2856, 1462, 1420,
Hydroxy ester 9: To a Raney Ni suspension [freshly prepared from Al/Ni
alloy (38.0 g) and NaOH (31.0 g, 775 mmol)] in EtOH (80 mL) S,O-
acetal 8 (3.77 g, 8.80 mmol) was added. The mixture was stirred for 24 h
under H2 (50 bar) at room temperature. Then the suspension was filtered
over a frit, and the filtration residue was washed with THF (3ꢂ100 mL).
The solvent was removed, and the crude product was purified by flash
chromatography (CH2Cl2/EtOAc 4:1). Hydroxy ester 9 (1.02 g, 45%) was
isolated as a colorless liquid. Rf =0.11 (CH2Cl2/EtOAc 4:1); [a]2D5 =ꢀ12.1
(c=1.06 in CH2Cl2); 1H NMR (500 MHz, CDCl3): d=0.86 (t, J=7.4 Hz,
3H), 0.89 (t, J=7.1 Hz, 3H), 1.30–1.49 (m, 5H), 1.57–1.64 (m, 4H), 1.67–
1.72 (m, 1H), 1.94–2.00 (m, 2H), 2.29–2.34 (m, 1H), 2.61 (brs, 1H), 3.67
(s, 3H), 3.76–3.80 (m, 1H), 3.90–3.94 (m, 1H), 4.09–4.11 ppm (m, 1H);
1379, 1309, 1253, 1191, 1065, 1038, 1005, 945, 911, 834, 806, 773, 663 cmꢀ1
;
MS (ESI): m/z: 455.0 [M+H]+; elemental analysis calcd (%) for
C19H39IO2Si: C 50.21, H 8.65; found: C 50.33, H 8.70.
Olefin 14: To a solution of 12 (1.58 g, 3.48 mol) in Et2O (60 mL) tBuLi
(1.5m in hexane, 5.10 mL, 7.65 mmol) was added at ꢀ788C. After stirring
Chem. Eur. J. 2011, 17, 13334 – 13340
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13337

P. Metz et al.
for 1 h at this temperature, a suspension of 2-acetylfuran (13) (574 mg,
5.21 mmol) and molecular sieves 4 ꢃ (500 mg) in Et2O (30 mL) was
added dropwise. The mixture was allowed to stir for 12 h at room tem-
perature before it was diluted with Et2O (60 mL) and then quenched
with saturated aqueous NaHCO3 solution (60 mL). The aqueous layer
was extracted with Et2O (2ꢂ50 mL), acidified with 2n HCl and extracted
again with Et2O (2ꢂ50 mL). Then the combined organic layers were
dried, the solvent was removed by evaporation, the residue was dissolved
in CH2Cl2 (50 mL), and concentrated aqueous HCl (1 drop) was added.
This solution was stirred for 1 h at room temperature and then treated
with saturated aqueous NaHCO3 solution (50 mL). The aqueous layer
was extracted with CH2Cl2 (3ꢂ50 mL), and the combined organic layers
were dried and evaporated. Final purification by flash chromatography
(pentane/CH2Cl2 5:1) gave 14 (1.04 g, 71% from 12) as a colorless liquid.
Rf =0.14 (pentane/CH2Cl2 5:1); [a]2D5 = +30 (c=1.25 in CH2Cl2);
1H NMR (500 MHz, CDCl3): d=0.01 (s, 3H), 0.03 (s, 3H), 0.85–0.90 (m,
15H), 1.31–1.44 (m, 6H), 1.51–1.64 (m, 4H), 1.83–1.92 (m, 2H), 1.91 (s,
3H), 2.41 (m, 1H), 3.80–3.86 (m, 3H), 5.92–5.94 (m, 1H), 6.17 (d, J=
3.3 Hz, 1H), 6.35–6.36 (m, 1H), 7.30 ppm (m, 1H); 13C NMR (126 MHz,
CDCl3): d=ꢀ4.70 (q), ꢀ4.58 (q), 12.12 (q), 13.98 (q), 14.37 (q), 18.08 (t),
18.14 (s), 24.99 (t), 25.97 (q), 28.67 (t), 31.74 (t), 40.49 (t), 43.36 (t), 44.59
(d), 69.81 (d), 75.63 (d), 81.57 (d), 104.27 (d), 110.90 (d), 125.71 (s),
126.99 (d), 140.95 (d), 156.36 ppm (s); IR (neat): n=2956, 2931, 2858,
1741, 1492, 1462, 1378, 1252, 1064, 1040, 1007, 947, 913, 833, 807, 773,
728, 675, 594 cmꢀ1; MS (ESI): m/z: 421.2 [M+H]+; elemental analysis
calcd (%) for C25H44O3Si: C 71.37, H 10.54; found: C 71.39, H 10.47.
1462, 1356, 1346, 1317, 1296, 1250, 1166, 1133, 1065, 1044, 1009, 994, 948,
914, 892, 828, 772, 740, 712, 657, 631, 611 cmꢀ1; MS (ESI): m/z: 529.2
[M+H]+, 546.2 [M+NH4]+; elemental analysis calcd (%) for
C27H48O6SSi: C 61.32, H 9.15, S 6.06; found: C 60.94, H 8.94, S 6.34.
Cyclohexene 17: To generate EtLi, freshly distilled EtI (255 mL,
3.19 mmol) was dissolved in Et2O (7 mL), and tBuLi (1.5m solution in
hexane, 4.33 mL, 6.49 mmol) was added to this solution at ꢀ788C. After
stirring for 1 h at this temperature and additional 1.5 h at room tempera-
ture, the resulting suspension was added dropwise to a solution of 16
(563 mg, 1.06 mmol) in THF (15 mL) at ꢀ788C. The reaction mixture
was stirred for 30 min at ꢀ788C and than for 1 h at room temperature.
The reaction was quenched with saturated aqueous NH4Cl solution
(10 mL), and the aqueous layer was extracted with Et2O (4ꢂ10 mL). The
combined organic layers were dried and filtered. After removal of the
solvent and purification by flash chromatography (pentane/EtOAc 3:2),
cyclohexene 17 (343 mg, 58%) was isolated as a white solid. Rf =0.36
(pentane/EtOAc 3:2); [a]2D5 =ꢀ27.6 (c=1.21 in CH2Cl2); 1H NMR
(500 MHz, CDCl3): d=0.02 (s, 3H), 0.03 (s, 3H), 0.81–0.91 (m, 12H),
1.00–1.03 (m, 6H), 1.10 (d, J=6.8 Hz, 3H), 1.24–1.33 (m, 2H), 1.35–1.56
(m, 8H), 1.58–1.75 (m, 3H), 1.93–1.99 (m, 2H), 2.01–2.19 (m, 1H), 2.13–
2.19 (m, 1H), 2.62–2.68 (m, 2H), 3.14 (brs, 1H), 3.77–3.89 (m, 4H), 3.96
(m, 1H), 4.71–4.74 (m, 1H), 5.29–5.67 ppm (m, 1H); 13C NMR
(126 MHz, CDCl3): d=ꢀ4.65 (q), ꢀ4.62 (q), 11.63 (q), 12.62 (q), 13.64
(q), 14.32 (q), 17.93 (t), 18.03 (t), 18.08 (s), 24.00 (t), 25.94 (q), 27.66 (t),
29.68 (t), 31.79 (t), 37.99 (d), 40.45 (t), 41.77 (d), 43.72 (t), 46.49 (d),
59.06 (d), 63.94 (d), 69.68 (d), 75.41 (d), 78.30 (d), 90.29 (d), 129.74 (d),
130.20 ppm (s); IR (KBr): n=3519 (broad), 2956, 2933, 2875, 2856, 1352,
Alcohol 15: Olefin 14 (875 mg, 2.08 mmol) was dissolved in THF
(15 mL) and BH3·THF (1m in THF, 4.16 mL, 4.16 mmol) was added
dropwise at 08C. After stirring for 3 h at 08C and further 3 h at room
temperature, water (0.7 mL), 2n NaOH (7.0 mL), and aqueous H2O2 so-
lution (30%, 7.0 mL) were added carefully at 08C. The mixture was
stirred for 1 h at room temperature, and then aqueous saturated Na2S2O3
solution (33 mL) was added. The separated aqueous layer was extracted
with Et2O (3ꢂ30 mL), and the combined organic layers were dried, fil-
tered, and evaporated. Purification by flash chromatography (pentane/
EtOAc 10:0.5) gave 15 (465 mg, 51%) as a colorless liquid. Rf =0.23
(pentane/EtOAc 10:0.5); [a]2D5 = +34.9 (c=1.18 in CH2Cl2); 1H NMR
(500 MHz, CDCl3): d=0.02 (s, 6H), 0.83–0.87 (m, 12H), 0.98 (t, J=
7.5 Hz, 3H), 1.17 (d, J=7.1 Hz, 3H), 1.24–1.29 (m, 2H), 1.35–1.38 (m,
2H), 1.48–1.50 (m, 2H), 1.54–1.59 (m, 4H), 1.68–1.76 (m, 1H), 1.96–1.99
(m, 2H), 3.04–3.07 (m, 1H), 3.43 (brs, 1H), 3.78–3.80 (m, 2H), 4.02–4.03
(m, 2H), 6.10 (d, J=3.1 Hz, 1H), 6.30–6.31 (m, 1H), 7.32–7.33 ppm (m,
1H); 13C NMR (126 MHz, CDCl3): d=ꢀ4.83 (q), ꢀ4.46 (q), 12.60 (q),
14.35 (q), 16.44 (q), 17.86 (t), 18.11 (s), 18.18 (t), 25.96 (q), 28.83 (t),
31.68 (t), 36.83 (d), 40.53 (t), 42.89 (t), 44.82 (d), 69.45 (d), 73.84 (d),
76.15 (d), 80.03 (d), 104.97 (d), 110.07 (d), 140.72 (d), 158.63 ppm (s); IR
(neat): n=3413 (broad), 2956, 2930, 2856, 1506, 1463, 1378, 1255, 1149,
1071, 1039, 1006, 946, 884, 834, 805, 774, 726, 663, 618, 599, 580 cmꢀ1; MS
(ESI): m/z: 421.2 [MꢀH2O+H]+, 439.2 [M+H]+; elemental analysis
calcd (%) for C25H46O4Si: C 68.44, H 10.57; found: C 68.79, H 10.63.
1254, 1207, 1171, 1158, 1068, 1005, 924, 887, 835, 808, 774, 645, 605 cmꢀ1
;
MS (ESI): m/z: 559.2 [M+H]+, 576.3 [M+NH4]+; elemental analysis
calcd (%) for C29H54O6SSi: C 62.32, H 9.74, S 5.74; found: C 62.48, H
9.82, S 5.38.
S,O-Acetal 19: Cyclohexene 17 (343 mg, 0.61 mmol) was dissolved in
CH2Cl2 (30 mL), and MeOH (10 mL) and NaHCO3 (390 mg, 4.64 mmol)
was added. This suspension was ozonized at ꢀ788C until a constant blue
coloration was reached. To remove excessive ozone, the reaction mixture
was purged with N2. Subsequently, the mixture was allowed to reach
room temperature. NaHCO3 was filtered off and rinsed with CH2Cl2
(20 mL). Then the solvent was evaporated at 308C. The residue was at
first dissolved in THF (10 mL) and after evaporation of the solvent dis-
solved again in CH2Cl2 (20 mL). Pyridine (98 mL, 1.21 mmol) and Ac2O
(58 mL, 0.61 mmol) were added at 08C, and the resulting solution was
stirred for 12 h at room temperature and further 12 h at reflux. There-
after it was diluted with Et2O (130 mL) and washed with 1n HCl
(20 mL) and saturated aqueous NaHCO3 solution (20 mL). The organic
layer was then dried and the solvent removed at 308C. Purification by
flash chromatography (pentane/EtOAc 4:1) gave the corresponding hemi-
acetal 18 (298 mg, 78%) as a light yellow oil. To a solution of 18 (223 mg,
0.36 mmol) in CH2Cl2 (30 mL) at first BF3·Et2O (100 mL, 0.79 mmol) and
5 min later thiophenol (340 mL, 3.33 mmol) were added, both at 08C.
After stirring for 1 h at room temperature, the reaction was quenched
with saturated aqueous NaHCO3 solution (10 mL). The aqueous layer
was extracted with CH2Cl2 (3ꢂ10 mL), and the combined organic layers
were dried and filtered. After evaporation of the solvent, the residue was
purified by flash chomatography (pentane/EtOAc 3:2) to afford 19
(164 mg, 76%) as a white solid. Rf =0.30 (pentane/EtOAc 3:2); m.p.
1168C; [a]2D5 =ꢀ18.1 (c=0.80 in CH2Cl2); 1H NMR (500 MHz, CDCl3):
d=0.82 (t, J=7.6 Hz, 3H), 0.89–0.95 (m, 6H), 1.21–1.24 (m, 1H), 1.29
(d, J=6.8 Hz, 3H), 1.30–1.62 (m, 10H), 1.66–1.71 (m, 2H), 1.93–1.97 (m,
2H), 2.25–2.30 (m, 2H), 2.70–2.77 (m, 3H), 3.72–3.73 (m, 4H), 3.82–3.84
(m, 2H), 4.01–4.02 (m, 1H), 4.72–4.74 (m, 1H), 4.88 (dd, J=1.6 Hz, J=
11.1 Hz, 1H), 7.36–7.46 ppm (m, 5H); 13C NMR (126 MHz, CDCl3): d=
11.49 (q), 11.62 (q), 13.19 (q), 14.05 (q), 17.68 (t), 18.89 (t), 22.13 (t),
29.42 (t), 31.03 (t), 31.05 (t), 37.45 (d), 39.36 (t), 41.47 (t), 45.41 (d), 51.63
(q), 55.06 (d), 64.99 (d), 68.69 (d), 76.02 (d), 79.18 (d), 82.21 (d), 84.82
(d), 100.43 (s), 129.70 (d), 130.21 (d), 131.88 (s), 136.43 (d), 173.69 ppm
(s); IR (KBr): n=3530 (broad), 2960, 2927, 2871, 1726, 1446, 1429, 1380,
1365, 1350, 1304, 1281, 1262, 1246, 1175, 1136, 1096, 1072, 1040, 1020,
964, 929, 904, 885, 853, 830, 805, 760, 732, 708, 697, 667 cmꢀ1; MS (ESI):
Sultone 16: Alcohol 15 (538 mg, 1.23 mmol) and Et3N (0.68 mL,
4.91 mmol) were dissolved in THF (12 mL), and vinylsulfonyl chloride
(0.22 mL, 2.43 mmol) was added at 08C. The reaction mixture was stirred
for 12 h at room temperature and then quenched with ice water (10 mL).
The aqueous layer was extracted with CH2Cl2 (10 mL), and the combined
organic layers were washed with 2n HCl (9 mL) and saturated aqueous
NaHCO3 solution (9 mL). After drying, filtration, and evaporation, the
crude product was purified by flash chromatography (CH2Cl2). Sultone
16 (571 mg, 88%) was isolated as colorless crystals. Rf =0.16 (CH2Cl2);
m.p. 1178C; [a]2D5 =ꢀ5.1 (c=1.23 in CH2Cl2); 1H NMR (500 MHz,
CDCl3): d=0.03 (s, 3H), 0.05 (s, 3H), 0.85–0.90 (m, 12H), 0.99–1.06 (m,
6H), 1.28–1.32 (m, 2H), 1.38–1.52 (m, 5H), 1.58–1.65 (m, 3H), 1.72–1.82
(m, 2H), 1.95–1.99 (m, 2H), 2.51–2.61 (m, 2H), 3.11–3.13 (m, 1H), 3.81–
3.89 (m, 3H), 5.01–5.03 (m, 1H), 5.17–5.19 (m, 1H), 6.03 (d, J=5.6 Hz,
1H), 6.52 ppm (dd, J=1.6 Hz, J=5.6 Hz, 1H); 13C NMR (75.5 MHz,
CDCl3): d=ꢀ4.58 (q), ꢀ4.52 (q), 12.24 (q), 13.87 (q), 14.32 (q), 17.58 (t),
18.03 (t), 18.09 (s), 25.97 (q), 29.10 (t), 30.12 (t), 31.87 (t), 33.86 (d), 40.50
(t), 43.68 (t), 45.33 (d), 57.50 (d), 69.86 (d), 75.70 (d), 78.58 (d), 78.96 (d),
85.58 (d), 92.26 (s), 135.78 (d), 139.72 ppm (d); IR (KBr): n=2935, 2859,
13338
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13334 – 13340

Total Synthesis of Pamamycin-649B
FULL PAPER
m/z: 616.2 [M+NH4]+; elemental analysis calcd (%) for C30H46O8S2: C
60.17, H 7.74, S 10.71; found: C 60.28, H 8.05, S 10.54.
0.02 (s, 3H), 0.06 (s, 3H), 0.74 (d, J=6.9 Hz, 3H), 0.78–0.86 (m, 9H),
0.91–0.95 (m, 9H), 1.05–1.14 (m, 1H), 1.27–1.39 (m, 3H), 1.40–1.50 (m,
4H), 1.50–1.70 (m, 7H), 1.75–1.84 (m, 2H), 1.90–2.03 (m, 3H), 2.10–2.15
(m, 1H), 2.48 (s, 6H), 3.13–3.14 (m, 1H), 3.65–3.69 (m, 1H), 3.71–3.79
(m, 1H), 3.81–3.84 (m, 1H), 4.12–4.15 (m, 1H), 4.20–4.22 ppm (m, 1H);
13C NMR (126 MHz, CDCl3): d=ꢀ4.84 (q), ꢀ3.21 (q), 10.07 (q), 12.29
(q), 13.86 (q), 14.33 (q), 18.64 (s), 18.74 (t), 21.27 (t), 22.74 (t), 26.37 (q),
28.29 (t), 30.67 (t), 30.74 (t), 31.39 (t), 31.90 (t), 37.92 (t), 39.22 (q), 41.74
(d), 47.36 (d), 55.63 (d), 61.38 (d), 73.20 (d), 75.29 (d), 77.18 (d), 79.67
(d), 80.51 (d), 178.32 ppm (s); MS (ESI): m/z: 556.4 [M+H]+.
Azide 20: To a solution of 19 (164 mg, 274 mmol) in toluene (2 mL) Ph3P
(86 mg, 329 mmol) and HN3 (1.43m in toluene, 249 mL, 356 mmol) were
added, and the mixture was cooled to 08C. At this temperature DIAD
(63 mL, 329 mmol) was added dropwise. After stirring for 1 h at room
temperature, the reaction was quenched with water (1 mL), and the sepa-
rated aqueous layer was extracted with Et2O (3ꢂ2 mL). The combined
organic layers were dried and filtered, and the solvent was removed.
Final purification of the crude product was achieved by flash chromatog-
raphy (pentane/EtOAc 2:1) to give 20 (167 mg, 98%) as a white solid.
Rf =0.62 (pentane/EtOAc 2:1); 1H NMR (500 MHz, CDCl3): d=0.83 (t,
J=7.6 Hz, 3H), 0.92 (t, J=7.2 Hz, 3H), 0.94 (t, J=7.4 Hz, 3H), 1.18–1.28
(m, 2H), 1.30 (d, J=6.9 Hz, 3H), 1.38–1.64 (m, 9H), 1.67–1.69 (m, 1H),
1.78–1.84 (m, 1H), 1.92–2.00 (m, 2H), 2.26–2.30 (m, 1H), 2.70–2.78 (m,
3H), 3.39–3.41 (m, 1H), 3.73–3.77 (m, 4H), 3.82 (m, 1H), 3.86–3.89 (m,
1H), 4.71–4.76 (m, 1H), 4.88 (dd, J=11.1 Hz, J=1.5 Hz, 1H), 7.35–
7.46 ppm (m, 5H); 13C NMR (126 MHz, CDCl3): d=11.61 (2 ꢂ q), 13.38
(q), 13.76 (q), 17.58 (t), 19.20 (t), 22.12 (t), 29.02 (t), 31.04 (t), 31.29 (t),
35.90 (t), 37.44 (d), 40.08 (t), 45.57 (d), 51.58 (q), 55.06 (d), 60.13 (d),
64.90 (d), 75.38 (d), 79.07 (d), 82.19 (d), 84.82 (d), 100.49 (s), 129.67 (d),
130.18 (d), 131.92 (s), 136.42 (d), 173.71 ppm (s); IR (KBr): n=2939,
2878, 2098, 1736, 1460, 1442, 1371, 1353, 1310, 1275, 1264, 1229, 1204,
Silyl ether 23: Acid 2 (12 mg, 21.6 mmol) was dissolved in THF (0.5 mL).
To this solution first Et3N (5.3 mL, 37.8 mmol) and 10 min later 2,4,6-tri-
chlorobenzoyl chloride (3.8 mL, 23.8 mmol) were added. The mixture was
allowed to stir for 2 h at room temperature. Subsequently, the solvent
was removed, and the residue was taken up in toluene (0.5 mL). This sus-
pension was added to a solution of 4 (19 mg, 56.9 mmol) and DMAP
(13.2 mg, 108 mmol) in toluene (0.5 mL). After rinsing with toluene (3ꢂ
0.3 mL), the reaction mixture was stirred for 24 h at reflux. The solvent
was removed, and the crude product was purified by flash chromatogra-
phy (pentane/EtOAc/Et3N 8:2:0.5) to afford 23 (15 mg, 80%) as a light
yellow oil. Rf =0.51 (pentane/EtOAc/Et3N 8:2:0.5); 1H NMR (500 MHz,
CDCl3): d=0.00 (s, 3H), 0.02 (s, 3H), 0.85–0.93 (m, 24H), 0.95 (d, J=
6.8 Hz, 3H), 1.10 (d, J=7.0 Hz, 3H), 1.18–1.21 (m, 1H), 1.24–1.72 (m,
21H), 1.82–1.98 (m, 7H), 2.20 (s, 6H), 2.26–2.30 (m, 1H), 2.55–2.58 (m,
2H), 3.49–3.51 (m, 1H), 3.56–3.57 (m, 1H), 3.64–3.74 (m, 2H), 3.86–3.88
(m, 1H), 3.98–4.01 (m, 1H), 4.08 (d, J=5.7 Hz, 1H), 4.88–4.90 (m, 1H),
5.12 (s, 2H), 7.28–7.35 ppm (m, 5H); 13C NMR (126 MHz, CDCl3): d=
ꢀ4.83 (q), ꢀ4.45 (q), 9.93 (q), 11.50 (q), 11.97 (q), 13.20 (q), 14.04 (q),
14.08 (q), 14.30 (q), 18.27 (s), 18.95 (t), 20.19 (t), 22.14 (t), 26.04 (q),
28.46 (t), 28.97 (t), 29.39 (t), 29.60 (t), 29.69 (t), 31.39 (t), 31.62 (t), 32.19
(t), 35.03 (t), 40.21 (q), 41.56 (d), 44.93 (d), 45.21 (d), 47.62 (d), 53.74 (d),
60.46 (d), 65.99 (t), 72.33 (d), 75.56 (d), 75.86 (d), 79.36 (d), 80.12 (d),
80.47 (d), 80.63 (d), 80.78 (d), 127.91 (d), 127.96 (d), 128.44 (d), 136.20
(s), 174.28 (s), 174.72 ppm (s); MS (ESI): m/z: 872.6 [M+H]+.
1169, 1130, 1077, 1024, 993, 966, 896, 842, 798, 755, 731, 704, 625 cmꢀ1
;
MS (ESI): m/z: 641.1 [M+NH4]+; elemental analysis calcd (%) for
C30H45N3O7S2: C 57.76, H 7.27, N 6.74, S 10.28; found: C 57.82, H 7.48, N
6.89, S 10.13.
Silyl ether 22: To a Raney Ni suspension [freshly prepared from Al/Ni
alloy (5.50 g) and NaOH (7.17 g, 179 mmol)] in EtOH (80 mL) azide 20
(198 mg, 317 mmol) dissolved in a small amount of EtOH was added. The
mixture was stirred for 24 h under H2 (50 bar) at room temperature.
Thereafter aqueous formalin solution (37%, 1.5 mL) was added, and the
mixture was stirred for additional 24 h under H2 (50 bar). Subsequently,
the suspension was filtered over a frit, and the filtration residue was
washed with EtOH (20 mL) and EtOAc/Et3N 20:1 (3ꢂ20 mL). The sol-
vent was removed, and the crude product was purified by flash chroma-
tography (pentane/EtOAc/Et3N 2:8:0.5). The resulting hydroxy ester 21
was isolated together with a small amount of N-dimethylated but not de-
sulfurized byproduct. This mixture (81 mg) was dissolved in CH2Cl2
(6 mL), and then 2,6-lutidine (62 mL, 532 mmol) and TBSOTf (122 mL,
530 mmol) were added at 08C. After stirring for 2 h at room temperature,
the reaction was quenched with saturated aqueous NaHCO3 solution
(5 mL). The separated aqueous layer was extracted with CH2Cl2 (3ꢂ
5 mL), and the combined organic layers were dried, filtered and evapo-
rated. Final purification by flash chromatography (pentane/EtOAc/Et3N
8:2:0.5) gave 22 (85 mg, 47% from 20) as a colorless oil. Rf =0.42 (pen-
tane/EtOAc/Et3N 8:2:0.5); [a]2D5 =ꢀ0.5 (c=0.61 in CH2Cl2); 1H NMR
(500 MHz, CDCl3): d=0.00 (s, 3H), 0.01 (s, 3H), 0.83–0.92 (m, 21H),
1.97–1.03 (m, 1H), 1.23–1.69 (m, 15H), 1.88–1.95 (m, 4H), 2.20 (s, 6H),
2.28–2.30 (m, 1H), 2.54–2.59 (m, 1H), 3.52–3.53 (m, 1H), 3.66 (s, 3H),
3.67–3.72 (m, 1H), 3.80–3.86 (m, 2H), 4.03–4.05 ppm (m, 1H); 13C NMR
(126 MHz, CDCl3): d=ꢀ4.77 (q), ꢀ4.70 (q), 10.61 (q), 11.95 (q), 14.16
(q), 14.30 (q), 18.42 (s), 18.88 (t), 20.15 (t), 22.17 (t), 26.19 (q), 29.11 (t),
29.48 (t), 29.84 (t), 31.61 (t), 32.43 (t), 35.08 (t), 40.23 (q), 43.42 (d), 47.89
(d), 51.28 (q), 53.51 (d), 60.52 (d), 73.08 (d), 75.64 (d), 79.19 (d), 79.53
(d), 80.18 (d), 174.77 ppm (s); IR (neat): n=2956, 2929, 2856, 2773, 1740,
1461, 1434, 1382, 1360, 1251, 1195, 1162, 1050, 1006, 964, 888, 835, 811,
773, 678 cmꢀ1; MS (ESI): m/z: 570.4 [M+H]+; elemental analysis calcd
(%) for C32H63NO5Si: C 67.44, H 11.14, N 2.46; found: C 67.55, H 10.88,
N 2.47.
Hydroxy ester 24: A solution of 23 (34 mg, 39.0 mmol) in MeCN/aqueous
HF (40%) 95:5 (0.91 mL) was stirred for 5 h at room temperature. Sub-
sequently water (3.5 mL) was added. The separated aqueous layer was
extracted with CH2Cl2 (3ꢂ5 mL), and the combined organic layers were
dried, filtered, and evaporated. Purification of the residue by flash chro-
matography (pentane/EtOAc/Et3N 2:8:0.5) gave 24 (27 mg, 91%) as a
light yellow oil. Rf =0.40 (pentane/EtOAc/Et3N 2:8:0.5); 1H NMR
(500 MHz, CDCl3): d=0.75 (d, J=6.9 Hz, 3H), 0.84–0.91 (m, 12H), 0.94
(t, J=7.6 Hz, 3H), 1.10 (d, J=7.0 Hz, 3H), 1.18–1.38 (m, 6H), 1.39–1.60
(m, 11H), 1.64–2.01 (m, 12H), 2.18 (s, 6H), 2.30–2.35 (m, 1H), 2.47–2.49
(m, 1H), 2.55–2.58 (m, 1H), 3.64–3.67 (m, 1H), 3.82–3.85 (m, 2H), 3.88–
3.91 (m, 1H), 3.96–4.03 (m, 2H), 4.06–4.09 (m, 1H), 4.86–4.89 (m, 1H),
5.12 (s, 2H), 7.28–7.34 ppm (m, 5H); 13C NMR (126 MHz, CDCl3): d=
10.01 (q), 11.76 (q), 11.91 (q), 13.10 (q), 13.23 (q), 14.04 (q), 14.29 (q),
18.01 (t), 18.93 (t), 20.21 (t), 22.21 (t), 27.85 (t), 28.47 (t), 28.88 (t), 29.18
(t), 29.39 (t), 31.45 (t), 31.54 (t), 31.79 (t), 35.34 (t), 38.84 (d), 40.20 (q),
41.49 (d), 45.21 (d), 45.34 (d), 53.43 (d), 60.80 (d), 66.00 (t), 72.46 (d),
76.03 (d), 77.26 (d), 79.80 (d), 80.09 (d), 80.22 (d), 80.47 (d), 80.78 (d),
127.91 (d), 127.97 (d), 128.45 (d), 136.19 (s), 174.37 (s), 174.75 ppm (s);
MS (ESI): m/z: 758.5 [M+H]+.
Pamamycin-649B (1 f): To a solution of 24 (10 mg, 13.2 mmol) in THF
(1 mL) Pd/C (10%, 2 mg) was added. The resulting suspension was
stirred for 12 h under H2 at room temperature. After removal of the sol-
vent and following flash chromatography (CH2Cl2/MeOH 9:1), seco acid
25 was isolated as a mixture with byproducts. It was dissolved in CH2Cl2
(20 mL). First, molecular sieves 4 ꢃ (300 mg) and DMAP (11.0 mg,
90.0 mmol) were added. Then, after stirring for 30 min at room tempera-
ture, 2,4,6-trichlorobenzoyl chloride (5.6 mL, 36 mmol) was added. The re-
action mixture was allowed to stir for further 48 h. Subsequently, the mo-
lecular sieves were filtered off, and the filtrate was evaporated. Finally,
the residue was purified by flash chromatography (pentane/EtOAc/Et3N
8:2:0.5) to afford pamamycin-649B (1 f) (4.5 mg, 53% from 24) as a light
yellow oil. Rf =0.35 (pentane/EtOAc/Et3N 8:2:0.5); [a]2D5 = +12.1 (c=
0.165 in CH2Cl2); 1H NMR (500 MHz, CDCl3): d=0.85–0.95 (m, 18H),
Acid 2: To a solution of 22 (45 mg, 79 mmol) in THF/MeOH 4:1 (4 mL)
1n LiOH (2 mL) was added. After stirring for 12 h at room temperature,
the mixture was acidified with 2n HCl (pH 5). The separated aqueous
layer was then extracted with CH2Cl2 (3ꢂ), and the combined organic
layers were dried and filtered. After evaporation, the crude poduct was
purified by flash chromatography (CH2Cl2/MeOH 8:2) to give 2 (18 mg,
41%) as a light yellow oil. Methyl ester 22 (21 mg, 47%) was also isolat-
ed. 2: Rf =0.28 (CH2Cl2/MeOH 8:2); 1H NMR (500 MHz, CDCl3): d=
Chem. Eur. J. 2011, 17, 13334 – 13340
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13339

P. Metz et al.
1.07 (d, J=6.9 Hz, 3H), 1.21–1.48 (m, 11H), 1.51–1.68 (m, 7H), 1.71–1.83
(m, 6H), 1.85–1.96 (m, 4H), 2.14–2.19 (m, 1H), 2.25 (s, 6H), 2.53–2.55
(m, 2H), 3.71–3.72 (m, 1H), 3.79–3.85 (m, 2H), 3.94 (m, 1H), 4.03 (m,
1H), 4.13 (m, 1H), 4.71–4.73 (m, 1H), 4.87–4.89 ppm (m, 1H); 13C NMR
(126 MHz, CDCl3): d=8.42 (q), 9.69 (q), 11.73 (q), 11.86 (q), 13.78 (q),
14.25 (q), 14.28 (q), 17.29 (t), 19.94 (t), 20.16 (t), 22.68 (t), 27.49 (t), 27.90
(t), 28.22 (t), 28.94 (t), 30.15 (t), 31.52 (t), 31.66 (t), 33.48 (t), 35.36 (t),
37.65 (d), 40.22 (q), 41.26 (d), 41.88 (d), 46.62 (d), 55.05 (d), 61.14 (d),
75.79 (d, 76.43 (d), 76.59 (d), 77.96 (d), 78.50 (d), 80.40 (d), 80.73 (d),
172.65 (s), 173.62 ppm (s); IR (neat): n=2961, 2930, 2874, 2811, 2778,
1736, 1458, 1378, 1325, 1269, 1236, 1194, 1180, 1139, 1113, 1074, 1013,
974, 947, 902, 871, 802 cmꢀ1; MS (ESI): m/z: 650.5 [M+H]+; HRMS (EI
positive, 70 eV) m/z calcd. for C38H67NO7: 649.4918 [M]+; found:
649.4933.
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Financial support of this work by the Deutsche Forschungsgemeinschaft
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Received: July 7, 2011
Published online: October 20, 2011
13340
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13334 – 13340