B. P. Gangadhar et al. / Tetrahedron Letters 45 (2004) 355–358
357
Figure 1. Left: Representative analytical reversed phase chromatograms of the crude O-glycopeptides obtained by TFA cleavage: (A) H-Tyr[b-
Glc(OAc) ]-Gly-Ala-NH (R , 27 min); (B) H-Tyr(b- -Glc)-Gly-Ala-NH (R , 26 min); (C) H-Tyr[b-Lac(OAc) ]-Gly-Ala-NH (R , 41 min); (D) H-
Ser[b- -Glc(OAc) ]-Gly-Ala-NH (R , 23min). Note: The major peaks contained the target peptides (>90% of the crude peptides). See Ref. 15 for
HPLC conditions. Right: Representative 500 MHz NMR spectrum showing the anomeric proton region of N-a-Ac-Trp-Arg-Tyr(b- -Glc)-NH in
O at 10 ꢁC. Data suggests that glycosylation reaction under these conditions is highly stereoselective (b anomer >98%). The peaks between 4.96
and 5.00 ppm is due to H O.
D-
4
2
t
D
2
t
7
2
t
D
4
2
t
D
2
D
2
2
solved in DMF (10 mL) and used directly for acylation
of the a-amnio group of the peptide resin without fur-
ther purification or isolation steps (Scheme 1). At the
end of stepwise solid phase synthesis, OAc-protection of
the glucose was removed with 6 mM NaOMe in 85%
DMF–MeOH. This solvent composition was found
optimal for resin swelling and complete deprotection.
Finally, the free peptide was obtained by standard TFA
cleavage. Alternatively, direct treatment of the fully
protected peptide resin with TFA gave the tetraacety-
lated glycopeptide. We have also successfully extended
this strategy for the synthesis of peptides containing
disaccharides (Table 1) and for the synthesis of
and is expected to provide an added impetus for
O-glycopeptide research.
References and Notes
1
2
3
. Hojo, H.; Nakahara, Y. Curr. Prot. Pept. Sci. 2000, 1, 23 –
8.
. Polt, R.; Palian, M. M. Drugs of the Future 2001, 26, 561–
76.
. Polt, R.; Porreca, F.; Szabo, L. Z.; Bilsky, E. J.; Davis, P.;
Abbruscato, T. J.; Davis, T. P.; Horvath, R.; Yamamura,
H. I.; Hruby, V. J. Proc. Natl. Acad. Sci. U.S.A. 1994, 91,
7114–7118.
4
5
dodecapeptides containing Thr(b-
Applicability of this method for the synthesis of peptides
containing either Fmoc AA(a- -Glc/Gal) or Fmoc
AAa/b- -GlcNAc/GalNAc) remains to be investigated.
D
-Glc) (not shown).
4. Salvador, L. A.; Elofsson, M.; Kihlberg, J. Tetrahedron
995, 5643–5656.
1
5
6
7
8
. Jensen, K. J.; Meldal, M.; Bock, K. J. Chem. Soc., Perkin
Trans. 1 1993, 2119–2129.
. Meldal, M.; Jensen, K. J. Chem. Soc., Chem. Commun.
D
D
1
990, 483–485.
Reversed phase analytical HPLC indicated that the
crude products contained greater than 90% of the target
glycosylated peptide (Fig. 1 left). Purified peptides also
had the expected mass (Table 1). As shown in the rep-
resentative 500 MHz proton NMR spectrum, all glyco-
peptides thus obtained contained >97% of the b-anomer
suggesting that glycosylation under these conditions is
stereoselective (Fig. 1 right and Table 1).
. Jansson, A. M.; Meldal, M.; Bock, K. J. Chem. Soc.,
Perkin Trans. 1 1992, 23, 1699–1707.
. Bielfeldt, T.; Peters, S.; Meldal, M.; Bock, K.; Paulsen, H.
Angew. Chem., Int. Ed. Engl. 1992, 31, 857–859.
9. Polt, R.; Szabo, L.; Treiberg, J.; Li, Y.; Hruby, V. J. J. Am.
Chem. Soc. 1992, 114, 10249–10258.
1
0. Balasubramaniam, A. Curr. Pharm. Des. 2003, 9, 1165–
1
175.
1. Parker, E.; Heek, M. V.; Stamford, A. Eur. J. Pharmacol.
002, 440, 173–187.
1
2
In summary, we have avoided the cumbersome purifi-
cation steps, and devised a rapid, economical and con-
venient method for the high yield and stereoselective
synthesis of O-glycopeptides. This method can now be
exploited for the synthesis of various glycopeptides re-
1
2. Balasubramaniam, A. Am. J. Surg. 2002, 183, 430–434.
1
3. General method for the glycosylation of N-a-Fmoc-Tyr/
Ser-OPfp: Fmoc-Tyr/Ser-OPfp (0.5 mmol, 1 equiv), b-
Glc(OAc) (1.17 g, 3mmol, 6 equiv) and CH Cl (10 mL)
were placed in a round bottom flask and N2 gas was
bubbled for 5 min. BF O (390 lL, 3mmol, 6 equiv)
ÁEt
D-
5
2
2
1;2
quired for SAR studies as well as other applications,
3
2