The complex natural product model selected for this
study (the glycopeptide vancomycin) is a treatment of
last resort for certain antibiotic-resistant Gram-positive
pathogens.6 The selection for this model was based upon
the known impact of sugar modification upon improving
the activity of vancomycin analogs against vancomycin-
resistance bacteria,4f,7 and the permissive nature of the
vancomycin GT GtfE.8 Vancomycin aglycon (3) was read-
ily obtained by acid hydrolysis of vancomycin,4f,9 and, with
the simple activated 2-chloro-4-nitrophenyl glycoside (1)
in hand, we attempted to form the monoglycosylated
vancomycin derivative (4) using a dual-GT-catalyzed
coupled reaction (Figure 1C). The optimized single-pot
reaction (50 mM Tris-HCl buffer, pH 8.5; 1.2 mM donor 1;
1 mM UDP; 1 mM vancomycin aglycon 3; 4 μM OleD
TDP16; 10 μM GtfE; 30 °C) was followed by analytical
HPLC (see Figure S5). Notably, conversion to the desired
product (4) in this one-pot reaction (47%) was comparable
to the GtfE-catalyzed production of 4 directly from UDP-
Glc and 3 (53%).3 To generate sufficient material for
downstream neoglycosylation, the dual-GT-catalyzed re-
action was scaled (200 mL reaction volume) which, after
deproteination and simple purification, afforded150 mg of
the desired product 4 (35% isolated yield; see Supporting
Information for full characterization) for subsequent neo-
glycosylation using representative sugars found within the
bacterial cell wall or appended to glycopeptides.
Figure 2. Structures of the natural glycopeptide antibiotics
vancomycin (5) and teicoplanin (6) and known natural products
containing D-forosamine.
acid, a main component of bacterial peptidoglycan. Among
this series, D-glucose, L-rhamnose, D-glucosamine, and
N-acetyl-muramic acid were commercially available, a repre-
sentative 20-N-acyl-D-glucolipid was synthesized as pre-
viously described,4f and D-forosamine and L-vancosamine
were generated via acid hydrolysis of spiramycin and alloc-
protected vancomycin, respectively.9 For the pilot reaction,
compound 4was dissolved in DMSO/AcOH, followed by the
addition of a 10-fold excess of D-glucose. The reaction was
A wide variety of uniquely functionalized carbohydrates
decorate the peptide backbone of naturally occurring
glycopeptides and other antibiotics. Most of these sugars
fall within the hexo- and 6-deoxyhexopyranosides and
include D-glucose, L-rhamnose, L-vancosamine, D-glucosa-
mine, and the 20-N-acyl-D-glucolipid found in teicoplanin
(6).10 In addition to these four sugars represented among
glycopeptides, we also selected the highly deoxygenated
D-forosamine from the macrolide spiramycin (7) and insec-
ticidal spinosyns (8) (Figure 2),11 and N-acetyl-muramic
(7) (a) Ge, M.; Chen, Z.; Onishi, H. R.; Kohler, J.; Silver, L. L.;
Kerns, R.; Fukuzawa, S.; Thompson, C.; Khane, D. Science 1999, 284,
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Cavaleri, M. Antimicrob. Agents Chemother. 2004, 48, 1118. (c) Patti,
G. J.; Kim, S. J.; Yu, T.-Y.; Dietrich, E.; Tanaka, K. S. E.; Parr, T. R.,
Jr.; Rafai Far, A.; Schaefer, J. J. Biol. Chem. 2009, 392, 1178. (d) Ritter,
T. K.; Mong, K-K. T.; Liu, H.; Nakatani, T.; Wong, C.-H. Angew.
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Figure 3. Neoglycosylation of the 60-alkoxyaminosugar-substi-
tuted vancomycin neoaglycon (4) (upper). The products of the
neoglycosylation reaction with corresponding conversions based
upon HPLC are illustrated (lower). Full characterization of 9ꢀ16
is presented in the Supporting Information.
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