Synthesis of Vancomycin from the Aglycon

Article abstract of DOI:10.1021/ja983504u

Vancomycin-resistant bacterial strains pose a serious threat to human health. Efforts to overcome vancomycin resistance by modifying the natural product have shown that the carbohydrates help modulate biological activity. To explore the mechanisms by which the carbohydrates function, it would be useful to have access to vancomycin derivatives containing different disaccharides. We now describe the synthesis of vancomycin from a readily available protected aglycon. This chemistry lays the groundwork for wide-ranging investigations of the roles of the carbohydrates in the biological activity of vancomycin. Moreover, in developing methods to glycosylate vancomcyin, we have extended the utility of the sulfoxide glycosylation reaction considerably by making it possible to use unhindered esters as neighboring groups. The chemistry we describe may also have implications for how to improve some other glycosylation methods.

Full text of DOI:10.1021/ja983504u

J. Am. Chem. Soc. 1999, 121, 1237-1244
1237
Synthesis of Vancomycin from the Aglycon
Christopher Thompson, Min Ge, and Daniel Kahne*
Contribution from the Department of Chemistry, Princeton UniVersity, Princeton, New Jersey 08544
ReceiVed October 5, 1998
Abstract: Vancomycin-resistant bacterial strains pose a serious threat to human health. Efforts to overcome
vancomycin resistance by modifying the natural product have shown that the carbohydrates help modulate
biological activity. To explore the mechanisms by which the carbohydrates function, it would be useful to
have access to vancomycin derivatives containing different disaccharides. We now describe the synthesis of
vancomycin from a readily available protected aglycon. This chemistry lays the groundwork for wide-ranging
investigations of the roles of the carbohydrates in the biological activity of vancomycin. Moreover, in developing
methods to glycosylate vancomcyin, we have extended the utility of the sulfoxide glycosylation reaction
considerably by making it possible to use unhindered esters as neighboring groups. The chemistry we describe
may also have implications for how to improve some other glycosylation methods.
Introduction
Vancomycin (1, Figure 1) is a glycopeptide antibiotic used
to treat methicillin-resistant Gram-positive infections. Vanco-
mycin-resistant bacterial strains pose a serious threat to human
health. Efforts to overcome vancomycin resistance by modifying
the natural product have shown that the carbohydrates help
modulate antibiotic activity. In fact, dramatic increases in activity
against vancomycin-resistant microorganisms can be produced
simply by attaching substituents to the C3 nitrogen of the
vancosamine sugar.1 Since vancomycin resistance arises from
a change in the dipeptide substrate that weakens its affinity for
the vancomycin binding pocket, it is not clear how modifying
the sugars, which do not contact the substrate, can lead to
improvements in activity.2 To explore the mechanisms by which
the carbohydrates function, it would be useful to have access
to vancomycin derivatives containing different carbohydrate
moieties.3 We recently reported chemistry to attach the van-
cosamine sugar to the pseudoaglycon of vancomycin.3c We now
describe the synthesis of vancomycin from a readily available
protected aglycon. This chemistry lays the groundwork for wide-
ranging investigations of the roles played by the carbohydrates
of vancomycin in biological activity. Moreover, in developing
methods to glycosylate vancomycin, we have extended the utility
of the sulfoxide glycosylation reaction considerably by making
it possible to use unhindered esters as neighboring groups. The
Figure 1. Glycopeptide antibiotic vancomycin.
solution we describe may also have implications for how to
improve some other glycosylation methods. Finally, now that
Evans and Nicolaou have finished making the aglycon,4 this
work formally completes the total synthesis of vancomycin.
Background
To construct vancomycin from the aglycon, we needed a good
method to make the glycosidic linkage to the 2,4,6-trisubstituted
phenol of amino acid 4 on the aglycon. A wide variety of natural
products contain glycosidic linkages to phenols.5 Because
phenols are not very good nucleophiles, successful glycosylation
usually requires basic conditions that generate the more reactive
phenolates.5a,b,6 One widely used approach to make glycosidic
linkages to phenols involves the SN2 displacement of anomeric
(1) The carbohydrates on vancomycin have been implicated in biological
activity. See, for example: (a) Rodriguez, M. J.; Snyder, N. J.; Zweifel,
M. J.; Wilkie, S. C.; Stack, D. R.; Cooper, R. D.; Nicas, T. I.; Mullen, D.
L.; Butler, T. F.; Thompson, R. C. J. Antibiot. 1998, 51, 560. (b) Malabarba,
A.; Nicas, T. I.; Thompson, R. C. Med. Res. ReV. 1997, 17, 69. (c) Williams,
D. H. Nat. Prod. Rep. 1996, 469.
(2) (a) Walsh, C. T.; Fisher, S. L.; Park, I.-S.; Prahalad, M.; Wu, Z.
Chem. Biol. 1996, 3, 21. For various hypotheses on how carbohydrate
derivatives of vancomycin can overcome bacterial resistance, see, for
example: (b) Sharman, G. J.; Try, A. C.; Dancer, R. J.; Cho, Y. R.; Staroske,
T.; Bardsley, B.; Maguire, A. J.; Cooper, M. A.; O’Brien, D. P.; Williams,
D. H. J. Am. Chem. Soc. 1997, 119, 12041. (c) Allen, N. E.; Le Tourneau,
D. L.; Hobbs, J. N. J. Antibiot. 1997, 50, 677.
(4) (a) Evans, D. A.; Wood, M. R.; Trotter, B. W.; Richardson, T. I.;
Barrow, J. C.; Katz, J. L. Angew. Chem., Int. Ed. 1998, 37, 2700. (b)
Nicolaou, K. C.; Takayanagi, M.; Jain, N. F.; Natarajan, S.; Koumbis, A.
E.; Bando, T.; Ramanjulu, J. M. Angew. Chem. Int. Ed. 1998, 37, 2717.
For other synthetic efforts toward the vancomycin aglycon, see: (c) Boger,
D. L.; Beresis, R. T.; Loiseleur, O.; Wu, J. H.; Castle, S. L. Bioorg. Med.
Chem. Lett. 1998, 8, 721. (d) Rama Rao, R. V.; Gurjar, M. K.; Reddy, K.
L.; Rao, A. S. Chem. ReV. 1995, 95, 2135.
(3) The vancomycin disaccharide has been synthesized by three different
groups but has never been attached to the aglycon: (a) Dushin, R. G.;
Danishefsky, S. J. J. Am. Chem. Soc. 1992, 114, 3471. (b) Nicolaou, K. C.;
Mitchell, H. J.; van Delft, F. L.; Rubsam, F.; Rodriguez, R. M. Angew.
Chem. 1998, 110, 1972. (c) Ge, M.; Thompson, C.; Kahne, D. J. Am. Chem.
Soc. 1998, 120, 11014.
(5) (a) Stachulski, A. V.; Jenkins, G. N. Nat. Prod. Rep. 1998, 173. (b)
Gonzalez, G. I.; Zhu, J. J. Org. Chem. 1997, 62, 7544. (c) Yoshioka, T.;
Aizawa, Y.; Fujita, T.; Nakamura, K.; Sasahara, K.; Kuwano, H.; Kinoshita,
T.; Horikoshi, H. Chem. Pharm. Bull. 1991, 39, 2124.
(6) (a) Conchie, J.; Levvy, G. A.; Marsh, C. A. AdV. Carbohydr. Chem.
1957, 12, 157. (b) Gervay, J.; Hadd, M. J. J. Org. Chem. 1997, 62, 6961.
10.1021/ja983504u CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/20/1999

1238 J. Am. Chem. Soc., Vol. 121, No. 6, 1999
Thompson et al.
Scheme 1a
fortunately, the use of pivaloate esters as protecting groups is
not compatible with the synthesis of vancomycin because the
conditions (basic or reductive) required for deprotection are too
harsh.8,9b Furthermore, because pivaloates sometimes impede
glycosylations involving hindered nucleophiles, they can be
problematic neighboring groups, even for substrates that can
withstand harsh deprotection conditions. The need to use
pivaloates as neighboring groups has been a significant limitation
of the sulfoxide glycosylation method. In the course of exploring
ways to glycosylate vancomycin, we have overcome this
limitation by finding a better way to suppress ortho ester
formation that permits the use of unhindered esters as neighbor-
ing groups.
a Trapping on the anomeric carbon of activated glycosyl donors
containing neighboring group esters leads to the desired â-glycosides
(path A). Trapping on the carbonyl carbon leads to ortho ester side
products (path B).
Results and Discussion
halides under basic conditions. Although this approach often
works well with unhindered phenolates, elimination of the
anomeric halide becomes a serious problem with hindered
phenolates.5a,7 Unfortunately, the aglycon of vancomycin is both
sterically hindered and highly sensitive to base.8,9 Under the
basic conditions typically used for phenol glycosylations, the
asparagine side chain would rearrange,8 and the amino acids
could racemize.4b,10
The case of vancomycin is further complicated because the
glycosidic bond to the phenol is 1,2-trans (â). The most widely
used approach for achieving stereochemical control in the
formation of â-glycosidic linkages involves using a C2 ester
capable of neighboring group participation.11-13 With many
glycosylation methods, the presence of a C2 ester group
decreases the reactivity of the glycosyl donor considerably. High
temperatures and extended reaction times are required in order
to activate the donor and achieve glycosylation.12 Under these
conditions, decomposition processes begin to dominate the
reaction, particularly when weakly nucleophilic acceptors are
used.
The fact that ortho ester formation dominates in the sulfoxide
glycosylation reaction when acetates are used as protecting
groups has puzzled us for many years. Acetates have been used
successfully with many other glycosylation methods that also
appear to go through an oxonium ion intermediate (e.g.,
trichloroimidate donors).12 In considering possible explanations
for the different outcomes, it occurred to us that most glyco-
sylation methods that work well with acetates as neighboring
groups employ Lewis acid catalysts such as BF3.12 It has long
been known that Lewis acids catalyze the rearrangement of ortho
esters to the corresponding â-glycosides.11,16 Therefore, we
reasoned that including BF3 in the sulfoxide glycosylation
reaction might suppress ortho ester formation and make it
possible to use acetates as neighboring groups. Unfortunately,
preliminary attempts to glycosylate a protected vancomycin
aglycon with several different glucose sulfoxides in the presence
of BF3 and Tf2O, conditions previously used to attach the
vancosamine sugar to the vancomycin pseudoaglycon,3c gave
no product.
An advantage of the sulfoxide glycosylation method is that
donor activation takes place readily at low temperatures under
mild conditions, even in the presence of electron-withdrawing
protecting groups.14 Unless the C2 ester is a pivaloate or
comparably hindered neighboring group, however, ortho ester
formation occurs instead of glycosylation (Scheme 1).15 Un-
This result was not entirely unexpected. A model study
involving the glycosylation of 2,6-dimethoxyphenol had shown
that no product was obtained unless 2,6-di-tert-butyl-4-meth-
ylpyridine (DTBMP) was included in the reaction (compare
entry 1 with entry 2, Table 1). The base presumably increases
the nucleophilicity of the phenol sufficiently to permit glyco-
sylation.17 Since we could not avoid the use of base, we decided
to try the reaction in the presence of both BF3 and DTBMP.
Brown and Kanner have shown that sterically hindered pyridine
bases prefer protic over Lewis acids.18 Therefore, we thought
that there was a reasonable chance that the base would perform
its function of increasing the nucleophilicity of the phenol while
the Lewis acid would suppress ortho ester formation. We
confirmed that glycosylation of the hindered phenol model
system with the perpivaloated glucosyl donor could be achieved
in the presence of BF3 if base was included in the reaction. As
hoped, the addition of BF3 did not interfere with the function
of the base (Table 1, entry 3).
(7) Strongly acidic conditions have also been used to form glycosidic
linkages to phenols, but yields can be low and stereoselectivity poor; see
ref 3c.
(8) Harris, C. M.; Kopecka, H.; Harris, T. M. J. Am. Chem. Soc. 1983,
105, 6915.
(9) Vancomycin is also sensitive to acidic and oxidative conditions,
see: (a) Nagarajan, R.; Schabel, A. A. J. Chem. Soc., Chem. Commun.
1988, 1306. (b) Adamczyk, M.; Grote, J.; Rege, S. Bioorg. Med. Chem.
Lett. 1998, 8, 885 and references therein.
(10) The vancomycin aglycon has been enzymatically glycosylated:
Solenberg, P. J.; Matsushima, P.; Stack, D. R.; Wilkie, S. C.; Thompson,
R. C.; Baltz, R. H. Chem. Biol. 1997, 4, 195.
(11) Wulff, G.; Rohle, G. Angew. Chem., Int. Ed. Engl. 1974, 13, 157.
(12) For a review on glycosylation methodology, see: Toshima, K.;
Tatsuta, K. Chem ReV. 1993, 93, 1503.
(13) Danishefsky has developed a good method for making 1,2-trans
linkages to phenols that involves nucleophilic attack on a 1,2-epoxy sugar
by a potassium phenolate. Glycosylation of a variety of phenols has been
demonstrated, but we did not feel that the strong basic conditions would
be amenable to vancomycin, see ref 3a. 2,6-Dimethoxyphenol has been
glycosylated using a trichloroimidate; the reaction required 24 h at room
temperature, see ref 3b.
(14) (a) Kahne, D.; Walker, S.; Cheng, Y.; Van Engen, D. J. Am. Chem.
Soc. 1989, 111, 6881. (b) Kim, S.-H.; Augeri, D.; Yang, D.; Kahne, D. J.
Am. Chem. Soc. 1994, 116, 1766. (c) Ikemoto, N.; Schreiber, S. L. J. Am.
Chem. Soc. 1992, 114, 2524. (d) Berkowitz, D. B.; Danishefsky, S. J.;
Schulte, G. K. J. Am. Chem. Soc. 1992, 114, 4518.
(15) (a) Kunz, H.; Harreus, A. Liebigs Ann. Chem. 1982, 41. (b) Sato,
S.; Nunomura, S.; Nakano, T.; Ito, Y.; Ogawa, T. Tetrahedron Lett. 1988,
33, 4097. (c) Seeberger, P. H.; Eckhardt, M.; Gutteridge, C. E.; Danishefsky,
S. J. J. Am. Chem. Soc. 1997, 119, 10064.
We next examined whether the presence of BF3 would
suppress ortho ester formation. As shown in Table 1, glycosy-
(16) Wang, W.; Kong, F. J. Org. Chem. 1998, 63, 5744.
(17) Under the conditions of entry 1 (Table 1), the â-glycoside is formed
stereospecifically. Although this outcome might have been anticipated on
the basis of our previous experience with similar nucleophiles,5a,b Crich
has reported mixtures of R- and â-phenylglycosides when hindered phenols
are glycosylated with pivaloated glycosyl sulfides activated with PHSOTf.
Crich has argued that glycosyl sulfides activated with PHSOTf and glycosyl
sulfoxides activated with Tf2O both generate anomeric triflates. However,
in cases involving neighboring group participation, these glycosylation
methods evidently do not react via the same intermediates since they produce
different stereochemical outcomes. See: (a) Crich, D.; Sun, S. J. Am. Chem.
Soc. 1998, 120, 435. (b) Crich, D.; Sun, S. Tetrahedron 1998, 54, 8321.
(18) Brown, H. C.; Kanner, B. J. Am. Chem. Soc. 1953, 75, 3865.

Synthesis of Vancomycin from the Aglycon
J. Am. Chem. Soc., Vol. 121, No. 6, 1999 1239
Scheme 3a
Table 1
a Glycosylations were performed by adding Tf2O (2 equiv) to the
sulfoxide (2 equiv) and 2,6-di-tert-butylmethylpyridine (4 equiv) at -78
°C in CH2Cl2, allowing the reaction to warm to -60 °C for 20 min,
and adding the 2,6-dimethoxyphenol (1 equiv) as a solution in CH2Cl2
with or without BF3 (10 equiv). The reaction was then warmed to -40
°C and quenched with saturated NaHCO3. b 2,6-Di-tert-butylmethylpy-
ridine (DTBMP) omitted from reaction. c The major product was the
ortho ester (21%).
a Conditions: (a) (i) 4 equiv of alloc-succinimide, 3 equiv of
NaHCO3, H2O/dioxane, rt, 3 h; (ii) 5 equiv of allyl bromide, 2 equiv
of NaHCO3, DMF, rt, 2 h; (iii) 10 equiv of allyl bromide, 5 equiv of
Cs2CO3, DMF, rt, 6 h; (iv) 10 equiv of PhSH, 1% HBr/HOAc, rt, 15
min, 63%, four steps; (b) 2 equiv of Cs2CO3, 5 equiv of PMBCl, DMF,
rt, 12 h, 98%; (c) (i) 18 equiv of Ac2O, 36 equiv of pyridine, 0.2 equiv
of DMAP, CH2Cl2, rt, 5 h; (ii) 10% TFA in CH2Cl2, rt, 10 min, 95%,
2 steps; (d) 3.2 equiv of 6, 3.2 equiv of Tf2O, 6.5 equiv of DTBMP,
CH2Cl2, -78 to -60 °C, 30 min, then 1 equiv of 14 and 20 equiv of
BF3‚Et2O, -78 to 0 °C, 1.5 h; (e) 4 equiv of Ph3P, 5:1 dioxane:H2O,
reflux, 2 h, 13%, 2 steps; (f) 2 equiv of BF3‚Et2O, 2 equiv of Tf2O,
CH2Cl2, then 4 equiv of 17 (Scheme 4), Et2O, -78 to -20 °C, 1 h,
60% plus 23% recovered 16; (g) 5% hydrazine, allyl alcohol:MeOH:
THF ) 1:1:1, rt, 4 h, 63%; (h) 50 equiv of Bu3SnH, 1 equiv of
PdCl2(PPh3)3, DMF:AcOH 1:1, rt, 10 min, 78%; (i) (i) 2 equiv of alloc-
succinimide, 2 equiv of NaHCO3, H2O/dioxane, rt, 2 h; (ii) 2 equiv of
allyl bromide, 2 equiv of KHCO3, DMF, rt, 1 h, 40% over two steps;
(j) 5 equiv of PMBCl, 10 equiv of Cs2CO3, DMF, rt, 2 h, 70%; (k) 20
equiv of allyl bromide, 50 equiv of Cs2CO3, molecular sieves, DMF,
rt, 6 h, 60%.
Scheme 2a
a Conditions: (a) (1) Bu2SnO, benzene, reflux, 12 h; (2) AcCl,
CH2Cl2, 0 °C, 2 h, 83% (8:1 C3 acetate:C2 acetate); (b) 4-azidobutyric
acid, oxalyl chloride, DMF (catalytic), CH2Cl2, 0 °C to rt, 3 h, then 9,
pyridine, CH2Cl2, rt 1 h, 94%; (c) p-toluenesulfonic acid, CH2Cl2:MeOH
1:3, rt 15 h, 82%; (d) AcCl, pyridine, CH2Cl2, 0 °C to rt, 2 h, 100%;
(e) m-CPBA, CH2Cl2, -78 to 0 °C, 2 h, 98%; (f) Tf2O, DTBMP,
CH2Cl2, -78 to -60 °C, 20 min, then 2,6-dimethoxyphenol and
BF3‚Et2O, -78 to -55 °C, 45 min, 62%; (g) Ph3P, H2O, dioxane, reflux,
3 h, 64%.
sylate the weakly nucleophilic phenol on the vancomycin
aglycon using a neighboring group that could be deprotected
selectively under mild conditions.
lation of the hindered phenol model system with peracetylated
glucose sulfoxide took place with complete stereochemical
control and in good yield in the presence of both BF3 and
DTBMP (compare entries 4 and 5, Table 1). The chemistry also
worked well when sulfoxide 6 (Scheme 2), which contains an
azidobutyryl group at C2,19 was used to glycosylate the model
phenol (entry 6, Table 1). This neighboring group was inves-
tigated because azidobutyryl esters can be removed under
conditions that do not cleave acetates.19 We found that the
azidobutyryl phenyl glycoside 7 can be deprotected to 13 in
64% yield with Ph3P in refluxing dioxane/H2O (Scheme 2),
conditions that were expected to be compatible with the entire
range of protecting groups and functionality on the vancomycin
pseudoaglycon. Thus, we finally had an approach to â-glyco-
Although success in a model system is encouraging, the scope
of a method can be evaluated only when it is applied to a real
system. Accordingly, 14 was prepared from vancomycin (1) in
59% yield over seven steps (Scheme 3). Following protection
of the amines, the carboxylic acid, and the phenols, the
glycosidic linkage to the aglycon was hydrolyzed using 1% HBr/
HOAc and thiophenol.20 The liberated phenol was temporarily
protected as a p-methoxybenzyl ether and was regenerated to
give 14 after acetylation of the two benzylic hydroxyls.
Treatment of 14 with sulfoxide 6 and triflic anhydride in the
presence of DTBMP and BF3 gave 15,21 the identity of which
(20) Ten equivalents of thiophenol was used to scavenge the cleaved
sugars, which prevents byproduct formation and the loss of protecting groups
from the aglycon.
(19) Kusumoto, S.; Sakai, K.; Shiba, T. Bull. Chem. Soc. Jpn. 1986, 59,
1296.
(21) 15 could not be completely purified, but the mass (ESI) was
consistent with the structure shown.

1240 J. Am. Chem. Soc., Vol. 121, No. 6, 1999
Thompson et al.
was verified after removal of the azidobutryl group by correla-
tion to a previously characterized degradation product of
vancomycin (16).3c Following HPLC purification, the yield for
the two-step sequence was 13%. If we assume a 60-65% yield
for removal of the azidobutyryl group, based on the studies in
the much simpler model system 7, the estimated yield for the
glycosylation of 2 is 20-25%. This is lower than the 62% yield
obtained for glycosylation in the model system; given the
difficulty of the case, however, we were pleased that the reaction
worked at all.
The synthesis of vancomycin was completed in three steps
as shown in Scheme 3.3c We have previously described the
chemistry to form the R-glycosidic linkage to the vancosamine
sugar using the sulfoxide glycosylation method.3c BF3 was used
in this glycosylation in order to suppress dehydradation of the
primary asparagine amide in vancomycin. Hence, including BF3
in the sulfoxide glycosylation reaction extends its utility to
acceptors containing amides and also permits the use of
unhindered esters such as acetates as neighboring groups.
For those interested in the total synthesis of vancomycin, we
note that it is possible to arrive at the protected aglycon 14 from
the known aglycon of vancomycin 18 (Scheme 3).22 Following
protection of the amine and the carboxylic acid as shown, the
phenol of amino acid 4 of the aglycon can be selectively
protected23 with p-methoxylbenzyl chloride and cesium carbon-
ate in the presence of the other three phenols and the two
alcohols to give 19. The remaining phenols can then be alkylated
with allyl bromide, and the benzylic alcohols can be acetylated.
Finally, the p-methoxybenzyl ether can be selectively removed
to give the desired protected aglycon 14. Now that Evans and
Nicolaou have reported their landmark syntheses of the van-
comycin aglycon,4 the work described here completes a formal
total synthesis of this elusive target.
Experimental Section
General Methods. Unless otherwise stated, all chemicals were
purchased from Aldrich or Sigma and used without further purification.
Vancomycin was a generous gift from Merck. Methylene chloride,
toluene, benzene, pyridine, and triethylamine were distilled from
calcium hydride under dry argon. Diethyl ether and tetrahydrofuran
were distilled from potassium benzophenone ketyl under dry argon.
DMF and ethyl acetate were dried over activated molecular sieves. All
air- or moisture-sensitive reactions were run under an atmosphere of
dry argon.
Analytical thin-layer chromatography (TLC) was performed on silica
gel 60 F254 plates (0.25 mm thickness) precoated with a fluorescent
indicator. The developed plates were examined under short-wave UV
light and stained with anisaldehyde. Flash chromatography24 was
performed using silica gel 60 (230-400 mesh) from EM Science. Radial
chromatography was performed on a Chromatatron from Harrison
Research using 1-mm circular plates. Analytical HPLC was performed
on a Hewlett-Packard Ti Series 1050 instrument. Preparative HPLC
was performed using a Hitachi L-6200A pump and a Waters 484 tunable
absorbance detector. Vancomycin compounds were monitored at an
absorbance wavelength of 285 nm.
NMR spectra were recorded on a JEOL GSX 270-MHz NMR
spectrometer or a Varian Inova 500-MHz/VNMR spectrometer. Chemi-
cal shifts (δ) are reported in parts per million (ppm) downfield from
tetramethylsilane. Coupling constants (J) are reported in hertz (Hz).
Multiplicities are abbreviated as follows: singlet (s), doublet (d), triplet
(t), quartet (q), multiplet (m), doublet of doublets (dd), apparent triplet
(apt), broad singlet (bs), pentet (p), and octet (o).
High-resolution mass spectra (FAB) were obtained at the University
of California at Riverside Department of Chemistry Mass Spectrometry
Facility.
Phenyl 3-O-Acetyl-4,6-O-benzylidene-1-thio-â-D-glucopyranoside
(9). Benzene (30 mL) was added to phenyl 4,6-O-benzylidene-1-thio-
â-D-glucopyranoside25 (524.3 mg, 1.45 mmol) and dibutyltin oxide
(399.6 mg, 1.6 mmol), and the solution was refluxed with a Dean Stark
trap for 6 h. The reaction was then cooled, filtered through Celite, and
concentrated. The residue was dissolved in 50 mL of CH2Cl2 and cooled
to 0 °C. AcCl was added (130 µL, 1.81 mmol), and the reaction was
stirred at 0 °C for 2 h and then filtered through a plug of silica gel
with 100% EtOAc. The filtrate was washed with saturated NaHCO3
(100 mL) and saturated NaCl (100 mL), dried over Na2SO4, and
concentrated. Purification by flash chromatography (40% EtOAc/
petroleum ether) gave 486.0 mg (83%) of 9 as an 8:1 mixture of C3:
C2 acetates: Rf 0.53 (40% EtOAc/petroleum ether); 1H NMR (CDCl3,
500 MHz) δ 7.36-7.59 (m, 10H), 5.49 (s, 1H, benzylic proton), 5.24
(apt, J ) 9 Hz, 1H, H3), 4.69 (d, J ) 10 Hz, 1H, H1), 4.39 (dd, J )
11, 4 Hz, 1H, H6), 3.78 (apt, J ) 9.5 Hz, 1H, H5), 3.53-3.61 (m, 3H,
H6′, H4, H2), 2.73 (s, 1H, C2 OH), 2.12 (s, 3H, C3 acetate); 13C NMR
(CDCl3, 500 MHz) δ 171.8, 137.6, 134.0, 131.9, 129.9, 129.3, 129.0,
126.9, 137.6, 134.0, 131.9, 129.9, 129.3, 129.0, 126.9, 102.2, 89.9,
78.9, 75.6, 72.3, 71.5, 69.3, 21.7; HR-MS (FAB) calcd for C21H22O6SNa
[M + Na+] 425.1035, found 425.1032.
Phenyl 2-(4-Azidobutyryl)-3-O-acetyl-4,6-O-benzylidene-1-thio-
â-D-glucopyranoside (10). To a solution of 4-azidobutyric acid17 (1.2
g, 9.3 mmol) in 35 mL of CH2Cl2 were added oxalyl chloride (4.4 mL
of a 2 M solution in CH2Cl2, 8.8 mmol) and 4 drops of DMF. The
solution was stirred at room temperature for 2.5 h (until the evolution
of gas had stopped). Then 21 mL of this azidobutyryl chloride solution
was added via syringe to a solution of 9 (481.6 mg, 1.20 mmol) and
pyridine (1.94 mL, 23.9 mmol) in 25 mL of CH2Cl2. The reaction was
stirred for 45 min at room temperature and then poured into 100 mL
of saturated NaHCO3. The aqueous layer was extracted with CH2Cl2
(3 × 50 mL). The organic extracts were combined, washed with 1 N
HCl (100 mL) and saturated NaCl (100 mL), dried over Na2SO4,
filtered, and concentrated. The residue was purified by flash chroma-
tography in 20% EtOAc/petroleum ether to give 575.5 mg (94%) of
10 as an 8:1 mixture of C2:C3 azidobutyrates: Rf 0.48 (25% EtOAc/
Conclusion
The chemistry described above extends the utility of the
sulfoxide glycosylation reaction significantly by making it
possible to use unhindered esters for â-glycoside formation.
Although pivaloate groups are effective at preventing ortho ester
formation, they introduce a new set of problems because they
are difficult to install and remove, which limits their utility to
molecules that are relatively stable. In addition, the need to use
pivaloate esters to achieve â-glycosylation sometimes results
in awkward protecting group manipulations. Therefore, the use
of BF3 to suppress ortho ester formation overcomes a significant
limitation of the sulfoxide method. Furthermore, our results
suggest that other glycosylation methods in which Lewis acid
catalysts are employed may benefit from the inclusion of
DTBMP or comparable pyridine bases, particularly when poor
nucleophiles are used as acceptors.
We note in closing that our primary motivation in developing
conditions to attach sugars to vancomycin was to make it
possible to study the biochemical roles of the carbohydrates on
vancomycin and other glycopeptide antibiotics. Although de
novo synthesis is now possible, the protected aglycon 14 can
be obtained far more quickly and in multigram quantitites via
degradation, as outlined. With methods now available to make
both glycosidic linkages of vancomycin, we should be able to
construct a wide range of carbohydrate derivatives of vanco-
mycin in which the two sugars are independently varied to
explore the roles of the sugars in biological activity.
(22) Marshall, F. J. J. Med. Chem. 1965, 8, 18.
(23) Seneci, P.; Ferrari, P.; Scotti, R.; Ciabatti, R. J. Antibiot. 1992, 45,
1633.
(24) Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923.
(25) Liptak, A.; Jodal, I.; Harangi, J.; Nanasi, P. Acta Chim. Hung. 1983,
113, 415.

Synthesis of Vancomycin from the Aglycon
J. Am. Chem. Soc., Vol. 121, No. 6, 1999 1241
petroleum ether); 1H NMR (CDCl3, 500 MHz) δ 7.33-7.48 (m, 10H),
5.49 (s, 1H, benzylic proton), 5.34 (apt, J ) 9.5 Hz, 1H, H3), 5.02
(dd, J ) 10, 8.5 Hz, 1H, H2) 4.82 (d, J ) 10 Hz, 1H, H1), 4.39 (dd,
J ) 10.5, 5 Hz, 1H, H6), 3.79 (apt, J ) 10 Hz, 1H, H6′), 3.67 (apt, J
) 9.5 Hz, 1H, H4), 3.55-3.60 (m, 1H, H5), 3.39 (t, J ) 7 Hz, 2H),
2.46 (o, J ) 7 Hz, 2H), 2.02 (s, 3H, C3 acetate), 1.92 (p, J ) 7 Hz,
2H); 13C NMR (CDCl3, 500 MHz) δ 171.5, 170.2, 136.9, 133.1, 131.8,
129.4, 129.3, 128.7, 128.5, 126.4, 101.7, 86.7, 78.3, 73.0, 71.1, 70.9,
68.6, 50.6, 31.2, 24.3, 21.0; HR-MS (FAB) calcd for C25H27N3O7SNa
[M + Na+] 536.1467, found 536.1491.
of saturated NaHCO3 and stirred for 5 min. The aqueous layer was
extracted with CH2Cl2 (3 × 25 mL). The organic extracts were dried
over Na2SO4, filtered, and concentrated. The residue was purified by
flash chromatography (35% EtOAc/petroleum ether) to give 19.0 mg
(62%) of 7: Rf 0.43 (40% EtOAc/petroleum ether); 1H NMR (CDCl3,
500 MHz) δ 7.04 (t, J ) 8 Hz, 1H, Ha on phenol), 6.58 (d, J ) 8 Hz,
2H, Hb on phenol), 5.24-5.36 (m, 3H, H2, H3, H4), 5.10 (d, J ) 7
Hz, 1H, H1), 4.26 (dd, J ) 12, 5 Hz, 1H, H6), 4.11 (dd, J ) 12, 2.5
Hz, 1H, H6′), 3.82 (s, 6H, 2 × OMe), 3.67-3.69 (m, 1H, H5), 3.32 (t,
J ) 7 Hz, 2H), 2.39 (t, J ) 7 Hz, 2H), 2.03 (s, 3H, acetate), 2.02 (s,
6H, 2 acetates), 1.82-1.86 (m, 2H); 13C NMR (CDCl3, 500 MHz) δ
171.8, 171.3, 171.1, 170.1, 154.0, 135.1, 125.6, 106.3, 101.8, 73.8,
72.9, 72.6, 69.3, 63.0, 57.0, 51.1, 31.6, 24.8, 21.4(3); HR-MS (FAB)
calcd for C24H31N3O12Na [M + Na+] 576.1805, found 576.1805.
3,4,6-Tri-O-acetyl-â-D-glucopyranosyl-2,6-dimethoxyphenol (13).
A solution of 7 (25.6 mg, 0.0463 mmol) in 5 mL of HPLC grade
dioxane was heated to reflux, and Ph3P (62 mg, 0.236 mmol) was added.
After 30 min, 1 mL of H2O was added, and refluxing was continued
for a further 2 h. The solution was then cooled, 1 mL of BuOH was
added, and the reaction was concentrated. Purification by flash
chromatography with 5% MeOH/CH2Cl2 followed by flash chroma-
tography with 50% EtOAc/petroleum ether gave 13.1 mg (64%) of 13
as a white solid: Rf 0.15 (50% EtOAc/petroleum ether); 1H NMR
(CDCl3, 500 MHz) δ 7.09 (t, J ) 8.5 Hz, 1H, Ha on phenol), 6.62 (d,
J ) 8.5 Hz, 2H, Hb on phenol), 5.18 (apt, J ) 9.5 Hz, 1H, H3), 5.11
(apt, J ) 9.5 Hz, 1H, H4), 4.60 (d, J ) 8 Hz, 1H, H1), 4.28 (dd, J )
12, 5 Hz, 1H, H6), 4.16 (dd, J ) 12, 2.5 Hz, 1H, H6′), 4.10 (bs, 1H,
C2 OH), 3.91 (dd, J ) 9.5, 8.0 Hz, 1H, H2), 3.87 (s, 6H, 2 × OMe),
3.67-3.71 (m, 1H, H5), 2.11 (s, 3H, acetate), 2.08 (s, 3H, acetate),
2.03 (s, 3H, acetate); 13C NMR (CDCl3, 500 MHz) δ 170.9, 170.7,
169.9, 153.1, 135.8, 125.6, 106.6, 105.6, 74.6, 72.7, 72.6, 68.7, 62.6,
56.5, 21.1, 21.0, 20.9; HR-MS (FAB) calcd for C20H26O11Na [M +
Na+] 465.1373, found 465.1390.
N-Alloc-tri-O-allyl-di-O-acetyl Vancomycin Aglycon Allyl Ester
(14). Vancomycin hydrochloride (3.0 g, 2 mmol) was dissolved in 25
mL of water and 25 mL of dioxane. NaHCO3 (554 mg, 6.6 mmol) in
10 mL of water was added to the reaction solution, followed by
N-(allyloxycarbonyloxy) succinimide (2 g, 8 mmol) in 10 mL of dioxane
at room temperature. The reaction was stirred at room temperature for
3 h and then poured into 1000 mL of acetone. The white suspension
was divided into four centrifuge tubes and centrifuged at 4000 rpm for
5 min. The precipitate was collected to give 3.8 g of N,N′-dialloc
vancomycin as a white solid. A portion of this white solid (2.7 g) was
subjected to the next reaction without further purification: Rf 0.4
(CHCl3/MeOH/H2O ) 3/2/0.5).
The crude N,N′-dialloc vancomycin (2.7 g) from the previous reaction
was dissolved in 10 mL of DMF and stirred at room temperature.
Ground KHCO3 (284 mg, 2.84 mmol) was added to the reaction
solution. The suspension was stirred at reduced pressure for 30 min,
and then allyl bromide (175 µL, 2.02 mmol) was added. The reaction
was stirred for 5 h at room temperature and poured into a mixture of
200 mL of acetone and 800 mL of diethyl ether. This white suspension
was divided into four centrifuge tubes and centrifuged at 5000 rpm for
15 min. The precipitate was collected and dried to give 3 g of crude
N,N′-dialloc vancomycin allyl ester. This crude material was subjected
to the next reaction without further purification: Rf 0.12 (20% MeOH/
CHCl3).
Phenyl 2-(4-Azidobutyryl)-3-O-acetyl-1-thio-â-D-glucopyranoside
(11). Compound 10 (575.5 mg, 1.12 mmol) was dissolved in 40 mL of
3:1 MeOH:CH2Cl2, and p-toluenesulfonic acid (90 mg, 0.473 mmol)
was added. The reaction was stirred for 15 h, and then 100 µL of
pyridine was added and the reaction concentrated. Purification of the
residue by flash chromatography with 65% EtOAc/petroleum ether
removed the minor isomer and gave 389.8 mg (82%) of pure 11: Rf
1
0.40 (75% EtOAc/petroleum ether); H NMR (CDCl3, 500 MHz) δ
7.32-7.46 (m, 5H), 5.07 (apt, J ) 9.5 Hz, 1H, H3), 4.95 (apt, J ) 9.5
Hz, 1H, H2), 4.77 (d, J ) 10 Hz, 1H, H2), 3.94 (dd, J ) 12.0, 3.5 Hz,
1H, H6), 3.83 (dd, J ) 12.0, 4.5 Hz, 1H, H6′), 3.74 (apt, J ) 9.5 Hz,
1H, H4), 3.45-3.48 (m, 1H, H5), 3.38 (t, J ) 7 Hz, 2H), 2.45 (o, J )
7 Hz, 2H), 2.07 (s, 3H, C3 acetate), 1.92 (p, J ) 7 Hz, 2H); 13C NMR
(CDCl3, 500 MHz) δ 171.7, 171.5, 132.7, 132.2, 129.3, 128.5, 86.0,
79.9, 77.2, 70.3, 69.4, 62.4, 50.6, 31.2, 24.3, 21.1; HR-MS (FAB) calcd
for C18H23N3O7SNa [M + Na+] 448.1154, found 448.1136.
Phenyl 2-(4-Azidobutyryl)-3,4,6-tri-O-acetyl-1-thio-â-D-glucopy-
ranoside (12). To a solution of 11 (367.5 mg, 0.864 mmol) at 0 °C in
50 mL of dry CH2Cl2 were added pyridine (683 µL, 8.64 mmol) and
acetyl chloride (308 µL, 4.32 mmol). The reaction was allowed to warm
to room temperature and quenched with 1 mL of MeOH after 1 h. The
reaction was diluted with 300 mL of EtOAc and washed with saturated
NaHCO3 (100 mL), 1 N HCl (100 mL), and saturated NaCl (100 mL).
The organic layer was dried over Na2SO4, filtered, and concentrated.
The residue was purified by flash chromatography with 50% EtOAc/
petroleum ether to give 440.2 mg (100%) of 12 as a white solid: Rf
1
0.56 (50% EtOAc/petroleum ether); H NMR (CDCl3, 500 MHz) δ
7.48-7.50 (m, 2H), 7.32-7.33 (m, 3H), 5.24 (apt, J ) 10 Hz, 1H,
H3), 5.05 (apt, J ) 10 Hz, 1H, H4), 4.99 (apt, J ) 10 Hz, 1H, H2),
4.72 (d, J ) 10.5 Hz, 1H, H1), 4.23 (dd, J ) 12, 5 Hz, 1H, H6), 4.18
(dd, J ) 12, 2.5 Hz, 1H, H6′), 3.71-3.75 (m, 1H, H5), 3.38 (apt, J )
7 Hz, 2H), 2.45 (o, J ) 7 Hz, 2H), 2.09 (s, 3H, acetate), 2.02 (s, 3H,
acetate), 1.99 (s, 3H, acetate), 1.92 (p, J ) 7 Hz, 2H); 13C NMR (CDCl3,
500 MHz) δ 171.2, 170.7, 170.3, 169.5, 133.2, 131.7, 129.1, 128.6,
85.9, 76.0, 74.0, 70.2, 68.4, 62.3, 50.5, 31.1, 24.3, 20.9, 20.7; HR-MS
(FAB) calcd for C22H27N3O9SNa [M + Na+] 532.1366, found 532.1381.
Phenyl 2-(4-Azidobutyryl)-3,4,6-tri-O-acetyl-1-sulfinyl-â-D-glu-
copyranoside (6). To a -78 °C solution of 12 (442.8 mg, 0.869 mmol)
in 20 mL of CH2Cl2 was added m-CPBA (220.6 mg, 68% purity, 0.869
mmol). The reaction was allowed to warm to -5 °C over 2 h and
quenched with 100 µL of Me2S. The reaction was poured into 100 mL
of saturated NaHCO3, and the aqueous layer was extracted with CH2Cl2
(3 × 50 mL). The organic extracts were dried over Na2SO4, filtered,
and concentrated. Purification of the residue by flash chromatography
gave 449.1 mg (98%) of 6 as an oil (∼1.5:1 mixture of sulfoxide
isomers): Rf 0.38 (50% EtOAc/petroleum ether); HR-MS (FAB) calcd
for C22H27N3O10SNa [M + Na+] 548.1315, found 548.1309.
2-(4-Azidobutyryl)-3,4,6-tri-O-acetyl-â-D-glucopyranosyl-2,6-
dimethoxyphenol (7). Phenyl 2-(4-azidobutyryl)-3,4,6-tri-O-acetyl-1-
sulfinyl-â-D-glucopyranoside (6) (51.8 mg, 0.0986 mmol) and 2,6-di-
tert-butyl-4-methylpyridine (40.8 mg, 0.197 mmol) were azeotroped
three times with toluene. Flame-dried 4-Å sieves and a stir bar were
added to the flask, followed by 4 mL of CH2Cl2. This solution was
stirred for 45 min and then cooled to -78 °C. Next, 166 µL of a stock
solution containing 100 µL of Tf2O and 900 µL of CH2Cl2 was added
(0.0986 mmol of Tf2O). The reaction was warmed to -60 °C,
maintained at this temperature for 20 min, and then cooled back to
-78 °C. 2,6-Dimethoxyphenol (8.6 mg, 0.0558 mmol) was dissolved
in 1 mL of CH2Cl2, and BF3‚Et2O (63 µL, 0.493 mmol) was added.
This solution was added to the activated sulfoxide by syringe. The
reaction was allowed to warm to -55 °C and then poured into 25 mL
To a solution of N,N′-dialloc vancomycin allyl ester (3 g) in 15 mL
of DMF was added Cs2CO3 (2.3 g, 7.1 mmol). This suspension was
stirred under reduced pressure for 15 min, and then allyl bromide (1.3
mL, 14.2 mmol) was added. The reaction was stirred at room
temperature overnight until TLC indicated complete reaction. The
suspension was precipitated with 200 mL of water. The white
suspension was divided into four centrifuge tubes and centrifuged
at 5000 rpm for 60 min. The precipitate was collected and loaded
onto a silica gel column (50 mm × 15 cm). Elution with 200 mL
of 5% MeOH/CHCl3 and then 500 mL of 20% MeOH/CHCl3 provided
2 g of semipure N,N′-dialloc-tri-O-allyl vancomycin allyl ester as a
white solid: Rf 0.65 (20% MeOH/CHCl3); HR-MS(FAB) calcd for
C86H99N9O28Cl2Na [M + Na+] 1798.5874, found 1798.5844; 1H NMR,
see Supporting Information.

1242 J. Am. Chem. Soc., Vol. 121, No. 6, 1999
Thompson et al.
To a solution of 232 mg of semipure N,N′-dialloc-tri-O-allyl
vancomycin allyl ester in 4 mL of acetic acid were added thiophenol
(75 µL, 0.730 mmol) and 2 mL of 3% HBr in acetic acid. The reaction
was stirred at room temperature for 15 min and then poured into 100
mL of H2O. The white precipitate was isolated by centrifugation.
Purification of the precipitate by flash chromatography (0 to 5% MeOH/
CH2Cl2) yielded 121 mg (63% over 4 steps from vancomycin) of
N-alloc-tri-O-allyl vancomycin aglycon allyl ester as a white solid: Rf
0.34 (10% MeOH/CHCl3); HR-MS (FAB) calcd for C69H72N8O19Cl2Na
dissolved in 1 mL of CH2Cl2, and then cooled to -78 °C. BF3‚OEt2 (2
µL, 0.0168 mmol) was added, followed by triflic anhydride (4 µL,
0.0247 mmol). A solution of sulfoxide 17 (20 mg, 0.0509 mmol) in
0.5 mL of Et2O was added to the reaction over 1 min. The reaction
was allowed to warm to -20 °C over 1 h and then quenched by addition
of a solution of 100 µL of methanol and 100 µL of DIEA. The solvent
was removed under reduced pressure, and the residue was purified on
a silica gel column (10 mm × 10 cm), eluting with CHCl3, followed
by 5% MeOH/CHCl3 to give 20 mg of crude product as a white solid.
This solid was repurified by reversed-phase HPLC using a Phenomenex
LUNA C18 column (21.2 × 250 mm), 5 µm particle size, eluting
with a 30-min linear gradient of 80% acetonitrile/0.1% acetic acid in
water to 100% acetonitrile/0.1% acetic acid, flow rate of 8 mL/min,
and ultraviolet (UV) detection at 285 nm. The peak at 12 min was
collected and concentrated to give 4.3 mg (22%) of recovered 16, while
the peak at 13 min was collected and concentrated to give 13.3 mg
(60%) of N,N′-dialloc-tri-O-allyl-hexa-O-acetyl vancomycin allyl ester
as a white solid: Rf 0.2 (5% MeOH/CHCl3); HR-MS (FAB) calcd for
C98H111N9O34Cl2Na [M + Na+] 2050.6508, found 2050.6458; 1H
NMR: see Supporting Information.
1
[M + Na+] 1409.4188, found 1409.4220; H NMR, see Supporting
Information.
To a solution of N-alloc-tri-O-allyl vancomycin aglycon allyl ester
(1.247 g, 0.898 mmol) in 20 mL of DMF were added Cs2CO3 (585
mg, 1.80 mmol) and PMBCl (609 µL, 4.49 mmol). The reaction was
stirred at room temperature overnight and then concentrated to an oil.
This oil was purified by flash chromatography (0 to 5% MeOH/CHCl3)
to give 1.338 g (99%) of N-alloc-tri-O-allyl-O-PMB vancomycin
aglycon allyl ester as a white solid: Rf 0.45 (10% MeOH/CHCl3); HR-
MS (FAB) calcd for C77H80N8O20Cl2Na [M + Na+] 1529.4764, found
1
1529.4833; H NMR, see Supporting Information.
To a solution of N-alloc-tri-O-allyl-O-PMB vancomycin aglycon allyl
ester (150 mg, 0.0995 mmol) in 2 mL CH2Cl2 were added pyridine
(40 µL, 0.497 mmol) and acetic anhydride (28 µL, 0.298 mmol),
followed by a catalytic amount of DMAP (2 mg). The reaction was
stirred at room temperature for 6 h and then quenched with 1 mL of
MeOH and concentrated in vacuo. The resulting oil was purified by
flash chromatography (0 to 5% MeOH/CHCl3) to give 125 mg (79%)
of N-alloc-tri-O-allyl-O-PMB-di-O-acetyl vancomycin aglycon allyl
ester as a white solid: Rf 0.5 (10% MeOH/CHCl3); HR-MS (FAB)
calcd for C81H84N8O22Cl2Na [M + Na+] 1613.4975, found 1613.5036;
1H NMR, see Supporting Information.
N,N′-Dialloc-tri-O-allyl-hexa-O-acetyl vancomycin allyl ester (5 mg,
0.00247 mmol) was dissolved in 500 µL of a solution of allyl alcohol/
methanol/THF ) 1:1:1 containing 5% NH2NH2.26 The reaction was
stirred at room temperature for 6 h and then quenched by addition of
100 µL of acetic acid. All solvents were removed under reduced
pressure, and the residue was purified by reversed-phase HPLC using
a Phenomenex LUNA C18 column (21.2 × 250 mm), 5 µm particle
size, eluting with a 30-min linear gradient of 50% acetonitrile/0.1%
acetic acid in water to 70% acetonitrile/0.1% acetic acid in water, flow
rate of 8 mL/min, and ultraviolet (UV) detection at 285 nm. The
fractions containing the desired product were collected and concentrated
to give 3.1 mg (70%) of N,N′-dialloc-tri-O-allyl vancomycin allyl ester
as a white solid: Rf 0.65 (20% MeOH/CHCl3); HR-MS (FAB) calcd
To a solution of N-alloc-tri-O-allyl-O-PMB-di-O-acetyl vancomycin
aglycon allyl ester (125 mg, 0.0785 mmol) in 5 mL of CH2Cl2 were
added 0.5 mL of TFA at room temperature. After 10 min, 25 mL of
toluene was added, and the reaction was concentrated in vacuo. The
residual white solid was purified by flash chromatography (5% MeOH/
CH2Cl2) to give 98 mg (85%) of 14 as a white solid: Rf 0.47 (10%
MeOH/CHCl3); HR-MS (FAB) calcd for C73H76N8O21Cl2Na [M + Na+]
1
for C86H99N9O28Cl2Na [M + Na+] 1798.5874, found 1798.5844; H
NMR, see Supporting Information.
N,N′-Dialloc-tri-O-allyl vancomycin allyl ester (3.9 mg, 0.00220
mmol) was dissolved in 0.5 mL of DMF, and then 0.5 mL of acetic
acid was added. A small amount of palladium dichloride-bis-
triphenylphosphine (∼2 mg) was added, and the reaction vessel was
filled with nitrogen. To this mixture was added, with vigorous stirring,
tributyltin hydride (two additions of 50 µL each at 5-min intervals).
The crude reaction mixture was precipitated with 30 mL of acetone in
a 50-mL centrifuge tube. The suspension was centrifuged, and the
supernatant was decanted to give a white solid. This white solid was
dissolved in 5 mL of water and kept at 0 °C overnight. The resulting
suspension was filtered through a disposable 13-µm syringe filter
(Whatman Inc.) to remove tin polymers, and the filtrate was concen-
trated. The residual solid was purified by reversed-phase HPLC using
a Phenomenex LUNA C18 column (21.2 × 250 mm), 5 µL particle
size, eluting with 0.1% acetic acid in water for 5 min and then a 30-
min linear gradient of 0.1% acetic acid in water to 20% acetonitrile/
0.1% acetic acid in water, flow rate of 7 mL/min, and ultraviolet (UV)
detection at 285 nm. The fractions containing the product were
combined and concentrated to give 2.6 mg (79%) of vancomycin (1)
as the acetic acid salt, a white solid. The synthetic vancomycin was
identical to an authentic sample of vancomycin by TLC, MS (ESI), 1H
NMR, and analytical HPLC (Phenomenex LUNA C18 column (4.6 ×
250 mm), 5 µm particle size, eluting with 0.1% TFA in water for 2
min and then a 28-min linear gradient of 0.1% TFA in water to 20%
acetonitrile/0.1% TFA in water, flow rate of 1 mL/min, and ultraviolet
(UV) detection at 285 nm; vancomycin had a retention time of 28 min).
1
1493.4400, found 1493.4368; H NMR, see Supporting Information.
N-Alloc-tri-O-allyl-penta-O-acetyl Vancomycin Pseudoaglycon
Allyl Ester (16). DTBMP (45.1 mg, 0.220 mmol) and 6 (60.7 mg,
0.116 mmol) were azeotroped three times with toluene in a 25-mL
round-bottom flask. Flame-dried 4-Å molecular sieves and 3 mL of
CH2Cl2 were added to the flask. The solution was stirred for 45 min
and then cooled to -78 °C. Tf2O (194 µL of a stock solution containing
100 µL of Tf2O and 900 µL of CH2Cl2, 0.116 mmol of Tf2O) was
added, and the reaction was allowed to warm to -60 °C over 15 min
and maintained at that temperature for 20 min. The reaction was then
cooled back to -78 °C, and 14 (52.5 mg, 0.0357 mmol) was added
with BF3‚Et2O (90 µL, 0.713 mmol) in 1 mL of CH2Cl2. The reaction
was allowed to warm to 0 °C over 1.5 h and then filtered through a
plug of silica gel into a flask containing 200 µL of pyridine. The filtrate
was concentrated, and the residue was purified by flash chromatography
(50% EtOAc/petroleum ether then 5% MeOH/CH2Cl2) to give 56.1
mg of crude 15 as a white solid. This material was dissolved in 4.5
mL of HPLC grade dioxane and heated to reflux. Ph3P (34 mg, 0.129
mmol) was added, and the reaction was refluxed for an additional 30
min. Then 1 mL of H2O was added, and refluxing was continued for
a further 2 h. At this point, the reaction was cooled and concentrated
in vacuo. The residue was purified by flash chromatography (50%
EtOAc/petroleum ether then 5% MeOH/CH2Cl2) and then radial
chromatography (5% MeOH/CH2Cl2) to give 24.7 mg of semipure 16.
Purification by reversed-phase HPLC (Phenomenex LUNA C18
column, 21 × 25 mm, 5 µm particle size, using a linear gradient of 70
to 90% CH3CN/H2O with 0.1% HOAc over 30 min, flow rate ) 7
mL/min, retention time ) 19 min) gave 7.9 mg (13%) of 16 as a white
solid: Rf 0.21 (5% MeOH/CH2Cl2); HR-MS (FAB) calcd for
C85H92N8O29Cl2Na [M + Na+] 1781.5274, found 1781.5245; 1H NMR,
see Supporting Information.
Vancomycin Aglycon (18).22 To a solution of vancomycin hydro-
chloride (3.7 g, 2.50 mmol) in 35 mL of water was added 3 mL of
concentrated HCl (aqueous). The reaction was refluxed for 5 min and
then cooled to room temperature. The white precipitate was collected
by suction filtration using a glass funnel equipped with a medium frit.
After filtration, the precipitate was washed with acetone and dried to
(26) The allyl alcohol was included in the reaction in order to prevent
the reduction of the allyl protecting groups on vancomycin by diimide, which
may be present in hydrazine.
Reconstruction of Vancomycin (1). The pseudoaglycon 16 (19 mg,
0.0108 mmol) was azeotroped with toluene three times (1 mL each),

Synthesis of Vancomycin from the Aglycon
J. Am. Chem. Soc., Vol. 121, No. 6, 1999 1243
Scheme 4a
give a brown solid. The crude product was used without further
purification: Rf 0.05 (CHCl3/MeOH/H2O ) 3/2/0.5).
N-Alloc-O-PMB Vancomycin Aglycon Allyl Ester (19). The crude
vancomycin aglycon 18 was dissolved in 20 mL of water and 25 mL
of dioxane. NaHCO3 (1.07 g, 12.75 mmol) in 10 mL of water was
added to the solution, followed by N-(allyloxycarbonyloxy) succinimide
(2 g, 8 mmol) in 10 mL of dioxane. The reaction was stirred at room
temperature for 3 h and then poured into 1000 mL of acetone. The
white suspension was divided into four centrifuge tubes and centrifuged
at 4000 rpm for 5 min. The precipitate was collected to give 3 g of
N-alloc vancomycin aglycon as a white solid. This material was
subjected to the next reaction without further purification: Rf 0.3
(CHCl3/MeOH/H2O ) 3/2/0.5).
The crude N-alloc vancomycin aglycon (200 mg) from the previous
reaction was dissolved in 3 mL of DMF and stirred at room temperature.
Ground KHCO3 (50 mg, 0.5 mmol) was added to the solution. The
suspension was stirred at reduced pressure for 30 min, and then allyl
bromide (70 µL, 0.835 mmol) was added. The reaction was stirred for
3 h and then quenched by addition of 1 mL of acetic acid. The solvent
was removed, and the residue was purified by flash chromatography
to give 50 mg (16%, not optimized) of N-alloc vancomycin aglycon
allyl ester as a white solid: Rf 0.32 (20% MeOH/CHCl3); HR-MS
(FAB) calcd for C60H61N8O19Cl2 [M + H+] 1267.3430, found 1267.3375;
1H NMR, see Supporting Information.
a Conditions: (a) (i) 4 equiv of alloc-succinimide, 3 equiv of
NaHCO3, H2O/dioxane ) 1/1, rt, 3 h; (ii) 1 M HCl/MeOH, 10 min, rt;
(iii) 3 equiv of Ac2O, pyridine, 0.1 equiv of DMAP, rt, 12 h, 56%
over three steps; (b) 1.2 equiv of PhSH, 3 equiv of BF3‚OEt2, CH2Cl2,
rt, 15 min, 88%; (c) 1 equiv of mCPBA, CH2Cl2, -78 to -20 °C, 1 h,
then 10 equiv of DMS, 86%.
next reaction without further purification: Rf 0.15 (30% EtOAc/
petroleum ether).
The N-alloc-vancosamine methyl glycoside (188 mg) was dissolved
in 3 mL of pyridine. DMAP (0.2 mg) was added to the reaction,
followed by acetic anhydride (0.5 mL). After 12 h, TLC showed
complete reaction. The reaction was quenched by addition of 0.5 mL
of methanol, and the solvents were removed under reduced pressure.
The residue was loaded onto a silica gel column (20 mm × 14 cm)
and eluted with 30% EtOAc/petroleum ether to give 104 mg (56%,
three steps from vancomycin) of 20 as a clear oil (R:â ) 2:1). R
1
anomer: Rf 0.3 (30% EtOAc/petroleum ether); H NMR (CDCl3, 500
MHz) δ 5.92-5.86 (m, 1H), 5.25 (dd, J ) 1.5, 17.4 Hz, 1H), 5.20
(dd, J ) 1.2, 10.4 Hz, 1H), 4.97 (s, 1H, H-4), 4.80 (d, J ) 4.6 Hz, 1H,
H-1), 4.75 (s, 1H), 4.53 (m, 1H), 4.46 (dd, J ) 5.8, 13 Hz, 1H), 4.10
(q, J ) 6.4 Hz, 1H, H-5), 3.33 (s, 3H), 2.16 (s, 3H), 2.12 (d, J ) 14.3
Hz, 1H, H-2), 1.97 (dd, J ) 4.6, 13.8 Hz, 1H, H-2′), 1.71 (s, 3H), 1.15
(d, J ) 6.4 Hz, 3H, H-6); 13C NMR (CDCl3, 500 MHz) δ 171.8, 157.0,
133.6, 118.4, 99.0, 74.5, 65.9, 63.5, 55.8, 53.7, 36.4, 24.7, 21.5, 18.0.
To a solution of N-alloc vancomycin aglycon allyl ester (7 mg,
0.00552 mmol) in 2 mL of DMF were added Cs2CO3 (5 mg) and
PMBCl (10 µL). The reaction was stirred for 2 h and then quenched
by addition of 1 mL of acetic acid, followed by 25 mL of water. The
precipitate was collected by suction filtration using a glass funnel
equipped with a medium frit. The precipitate was purified by reversed-
phase HPLC using a Phenomenex LUNA C18 column (21.2 × 250
mm), 5 µm particle size, eluting with a linear gradient of 30%
acetonitrile/0.1% acetic acid in water to 65% acetonitrile/0.1% acetic
acid in water over 40 min and then 65% acetonitrile/0.1% acetic acid
in water to 70% acetonitrile/0.1% acetic acid in water over 5 min, flow
rate of 7 mL/min, and ultraviolet (UV) detection at 285 nm. The
fractions containing the product were combined and concentrated to
give to give 5 mg (71%) of 19 as a white solid: Rf 0.51 (20% MeOH/
CHCl3); HR-MS (FAB) calcd for C68H68N8O20Cl2Na [M + Na+]
1
â anomer: Rf 0.27 (30% EtOAc/petroleum ether); H NMR (CDCl3,
500 MHz) δ 5.93-5.86 (m, 1H), 5.26 (d, J ) 17 Hz, 1H), 5.21 (d, J
) 10.4 Hz, 1H), 5.02 (s, 1H, H-4), 4.75 (bs, 1H), 4.58-4.52 (m, 2H),
4.47-4.44 (dd, J ) 5.5, 12.8 Hz, 1H), 3.87 (q, J ) 6.4 Hz, 1H, H-5),
3.52 (s, 3H), 2.15 (s, 3H), 2.10 (t, J ) 9 Hz, 1H), 2.05 (d, J ) 14 Hz,
1H), 1.625 (s, 3H), 1.20 (d, J ) 6.4 Hz, 3H, H-6); 13C NMR (CDCl3,
500 MHz) δ 171.5, 155.0, 133.5, 118.6, 100.2, 77.1, 69.1, 66.0, 57.3,
55.2, 39.0, 22.9, 21.5, 18.0; HR-MS (FAB) calcd for C14H23NO6Na
[M + Na+] 324.1423, found 324.1416.
1
1409.3824, found 1409.3749; H NMR, see Supporting Information.
N-Alloc-tri-O-allyl-di-O-acetyl Vancomycin Aglycon Allyl Ester
(14). To a solution of N-alloc-O-PMB vancomycin aglycon allyl ester
(10 mg, 0.00721 mmol) in 1 mL of DMF was added Cs2CO3 (13.5
mg, 0.0416 mmol). This suspension was stirred under reduced pressure
for 15 min, and then allyl bromide (12 µL) was added. The reaction
was stirred at room temperature for 7 h and then quenched by addition
of 1 mL of acetic acid, followed by 25 mL of water. The precipitate
was collected by suction filtration using a glass funnel equipped with
a medium frit. The precipitate was then purified by reversed-phase
HPLC using a Phenomenex LUNA C18 column (21.2 × 250 mm), 5
µm particle size, eluting with a 30-min linear gradient of 50%
acetonitrile/0.1% acetic acid in water to 90% acetonitrile/0.1% acetic
acid in water, flow rate of 7 mL/min, and UV detection at 285 nm.
The fractions containing the pure product were combined and evapo-
rated to give 6 mg (59%) of N-alloc-tri-O-allyl-O-PMB vancomycin
aglycon allyl ester as a white solid. This material was identical by TLC,
Phenyl 3-(N-Allyloxycarbonyloxy)-4-O-acetyl-1-thio-2,3,6-trideoxy-
3-C-methyl-r,â-L-lyxo-hexopyranoside (21) (Scheme 4). Compound
20 (170 mg, 0.569 mmol) was azeotroped with toluene three times
and then dissolved in 7 mL of CH2Cl2. PhSH (117 µL, 1.14 mmol)
was added, followed by BF3‚OEt2 (77 µL, 0.626 mmol). TLC showed
complete reaction after 60 min. The reaction was quenched by addition
of 20 mL of saturated NaHCO3. The CH2Cl2 layer was separated, and
the aqueous layer was further extracted with CH2Cl2 (3 × 20 mL).
The CH2Cl2 layers were combined, dried over anhydrous sodium sulfate,
filtered, and concentrated to give a clear oil. This oil was loaded onto
a silica gel column (30 mm × 14 cm) and eluted with 30% EtOAc/
petroleum ether to give 190 mg (88%) of 21 as a white solid (R:â )
1:2): Rf 0.40 (30% EtOAc/petroleum ether). â anomer: 1H NMR
(CDCl3, 500 MHz) δ 7.60 (d, 2H), 7.38-7.28 (m, 3H), 5.95-5.88 (m,
1H), 5.30 (dd, J ) 1.6, 17.4 Hz, 1H), 5.22 (dd, J ) 1.2, 10.4 Hz, 1H),
5.00-4.96 (m, 2H, H-4, H-1), 4.79 (s, 1H), 4.55 (m, 1H), 4.47 (dd, J
) 5.8, 13.2 Hz, 1H), 3.93 (q, J ) 6.4 Hz, 1H, H-5), 2.3 (d, J ) 12.3
Hz, 1H, H-2), 2.17 (s, 3H), 1.95 (t, J ) 12.5 Hz, 1H, H-2′), 1.65 (s,
3H), 1.23 (d, J ) 6.4 Hz, 3H, H-6); 13C NMR (CDCl3, 500 MHz) δ
171.66, 155.00, 134.70, 133.45, 132.25, 131.73, 129.53, 128.19, 118.60,
81.81, 73.16, 71.89, 66.06, 55.20, 38.55, 21.49, 18.50. R anomer: 1H
NMR (CDCl3, 500 MHz) δ 7.60-7.50 (m, 2H), 7.37-7.20 (m, 3H),
5.95-5.88 (m, 1H), 5.63 (dd, J ) 2.5, 6.7 Hz, 1H, H-1), 5.32 (dd, J )
1.2, 17.1 Hz, 1H), 5.23 (d, J ) 10.4 Hz, 1H), 5.00 (s, 1H, H-4), 4.90
(bs, 1H), 4.58-4.47 (m, 3H), 2.61-2.56 (m, 1H, H-2), 2.30-2.27 (dd,
J ) 1.8, 14.3 Hz, 1H, H-2′), 2.19 (s, 3H), 1.79 (s, 3H), 1.19 (d, J )
6.4, 3H, C-6 Me); 13C NMR (CDCl3, 500 MHz) δ 171.58, 155.00,
136.55, 133.51, 132.26, 131.73, 129.59, 127.85, 118.57, 83.64, 74.67,
66.05, 64.93, 54.18, 37.85, 24.65, 17.66; HR-MS (EI) calcd for
C19H25NO5SNa [M + Na+] 402.1351, found 402.1360.
1
ESI-MS, and H NMR to the compound obtained previously by the
other route (degradation of protected vancomycin derivative).
The synthesis of 14 from N-alloc-tri-O-allyl-O-PMB vancomycin
aglycon allyl ester was described above.
Methyl 3-(N-Allyloxycarbonyloxy)-2,3,6-trideoxy-3-C-methyl-r,â-
L-lyxo-hexopyranoside (20) (Scheme 4). To a solution of N,N′-dialloc
vancomycin (1.0 g crude) in 8 mL of methanol was added 1.2 mL of
concentrated aqueous HCl. The reaction was stirred at room temperature
for 10 min, and then the solvent was removed in vacuo. The residual
green oil was suspended in 200 mL of acetone and then centrifuged at
4000 rpm for 5 min. The clear supernatant was collected and
concentrated to give a green oil. This oil was loaded onto a silica gel
column and eluted with EtOAc to give crude N-alloc-vancosamine
methyl glycoside (188 mg) as a clear oil. This oil was subjected to the

1244 J. Am. Chem. Soc., Vol. 121, No. 6, 1999
Thompson et al.
Phenyl 3-(N-Allyloxycarbonyloxy)-4-O-acetyl-1-sulfinyl-2,3,6-
trideoxy-3-C-methyl-L-lyxo-hexopyranoside (17) (Scheme 4). The
vancosamine sulfide 21 (78 mg, 0.207 mmol) was dissolved in 10 mL
of CH2Cl2 and cooled to -78 °C. m-CPBA (39.8 mg of 64% purity,
0.207 mmol) was added, and the reaction was slowly warmed to -20
°C over 1 h. TLC showed complete reaction. The reaction was quenched
by addition of 100 µL of dimethyl sulfide. Ten milliliters of saturated
NaHCO3 was added, and the CH2Cl2 layer was extracted. The aqueous
layer was further extracted with CH2Cl2 (3 × 10 mL). The CH2Cl2
layers were combined, dried over anhydrous sodium sulfate, filtered,
and concentrated to a clear oil. This oil was loaded onto a silica gel
column (30 mm × 10 cm) and eluted with 60% EtOAc/petroleum ether
to give 70 mg (86%) of 17 as a white solid: Rf 0.12 and 0.10 (40%
EtOAc/petroleum ether).
Acknowledgment. This work was supported by Interneuron
Pharmaceuticals, Merck Research Laboratories, and the National
Institutes of Health.
Supporting Information Available: 1H NMR (500 MHz)
spectra of nine vancomycin intermediates (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JA983504U