The parallel synthesis of a disaccharide library using a solid phase, peptide-templated strategy.

Article abstract of DOI:10.1039/b313571c

A novel strategy for the synthesis of oligosaccharides, involving the use of a solid phase peptide template, has been successfully applied to the construction of a twelve member disaccharide library.

Full text of DOI:10.1039/b313571c

The parallel synthesis of a disaccharide library using a solid phase,
peptide-templated strategy
Jessica Burt,a Tony Deanb and Stuart Warriner*a
a School of Chemistry and The Astbury Centre, University of Leeds, Leeds, West Yorkshire, UK.
E-mail: S.L.Warriner@chem.leeds.ac.uk; Fax: 0113 3436565; Tel: 0113 3436437
b GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire, UK
Received (in Cambridge, UK) 28th October 2003, Accepted 24th November 2003
First published as an Advance Article on the web 12th December 2003
A novel strategy for the synthesis of oligosaccharides, involving
the use of a solid phase peptide template,1 has been successfully
applied to the construction of a twelve member disaccharide
library.
backbone and the sugar units. In the parallel synthesis each of the
three glycosyl donors were added to four portions of resin via an
extended coupling step. Another glycine residue was added as a
spacer unit followed by the four glycosyl acceptor building blocks
to each of the different glycosyl donor-bearing resin portions (e.g.
6). A final glycine residue was added and its Fmoc group left intact.
The preparation of the twelve peptide templates (e.g. 7) took only
2 days to complete. The synthesis of one library member is shown
in Scheme 2.
The resin-bound peptide templates were then exposed to the
glycosidation conditions (NIS, cat. TMSOTf, 4 Å mol. sieves, THF
: CH2Cl2 4 : 1, 20 h) and the final Fmoc group removed. Liberation
of the target disaccharides from the template is performed under
basic conditions, however, our original protocol required an
aqueous work-up to isolate the target disaccharide.2 Such manip-
ulations are not desirable in parallel synthesis so the use of
alternative cleavage conditions was investigated. It was found that
when small quantities of NaOH were used (NaOH (1 mg) in
methanol : THF (2 : 8, 2 ml, 5 h)) complete cleavage of the products
was effected and work up could be avoided. The resin was agitated
on a rotating wheel during glycosidation and cleavage steps.
Mass spectral analyses showed that the target disaccharides had
all been prepared successfully. Preparative reverse phase HPLC
was used to separate the a and b anomers of each of the
disaccharides. All the disaccharides were successfully separated
and each anomer fully characterised by 1H and 13C NMR
spectroscopy. Structures, yields and anomeric ratios are shown in
Table 1. Theoretical yields were calculated from the loading of the
resin as quoted by the manufacturer. Quoted yields represent the
The solid phase synthesis of glycosides is highly desirable as
supported synthesis is highly amenable to parallel and automated
technologies.1 We recently reported a solid supported approach to
disaccharide synthesis in which monosaccharide building blocks
are first attached to a peptide template.2–4 Following preparation of
a peptide decorated with glycosyl donors and acceptors, glycosida-
tion is performed on a solid phase. Cleavage of base labile
carbonate linkages then separates the target disaccharides from the
support. Preliminary studies revealed highly efficient reactions and
interesting selectivities when carbohydrates were prepared under
these conditions. Peptide templated approaches to glycoside
synthesis are easily transferred to the solid phase due to the highly
optimised procedures for solid phase peptide synthesis. In order to
demonstrate the applicability of this strategy to parallel synthesis
and future automation we now report the application of this
methodology to the synthesis of a twelve membered disaccharide
library.
Tribenzylated thioglycosides of glucose, mannose and galactose
(2) were prepared using standard protocols;5 these were then
coupled to protected hydroxyproline (Hyp) (1)6 via a mixed
carbonate link between the hydroxyl group of Hyp and the 6-OH of
the sugars to form the glycosyl donor building blocks (e.g. 3) in
yields of 60–80%. Methyl glycosides of glucose, mannose and
galactose were BDA protected7 and then coupled to Hyp in an
analogous fashion to give four glycosyl acceptor units (e.g. 5).
Typical examples are shown in Scheme 1.
Peptide templates were then constructed in a parallel manner on
Aminomethyl Novagel™ resin using standard Fmoc peptide
coupling protocols.8 Syntheses were performed in 3 ml fritted
plastic tubes on a 16 port vacuum tank. Agitation was not required
during peptide coupling. Two glycine residues were added prior to
the first building block to avoid any clashes between the resin
Scheme 1 Synthesis of the galactose donor and acceptor building blocks
(Pfp = pentafluorophenyl): a) COCl2, DCM, py, 278 °C to RT, then 2,
DCM, py; b) COCl2, DCM, py, 278 °C to RT, then 4, DCM, py.
Scheme 2 Synthesis of peptide template bearing galactose glycosyl donor
and acceptor building blocks. a) Fmoc-GlyOH, HOBt, HBTU, DIPEA; b)
20% piperidine, DMF; c) 3, HOBt; d) 5, HOBt.
454
C h e m . C o m m u n . , 2 0 0 4 , 4 5 4 – 4 5 5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Table 1 Disaccharide library prepared using peptide templated methodology
a Ratio a : b determined by NMR and HPLC. b Overall yield for synthesis, including peptide assembly. c The configuration of the major isomer was
determined from the 1JC1–H1 value.
2 D. R. Greenwell, A. F. Ibnouzaki and S. L. Warriner, Angew. Chem., Int.
Ed., 2002, 41, 1215.
cumulative yield for the peptide assembly and the subsequent
glycosidation, cleavage and HPLC steps, demonstrating the highly
efficient nature of the reaction sequence. Typically, syntheses
performed on 50 mg of resin yielded 10 mg of the major
disaccharide. It is notable that, apart from being mixtures of
anomers, the products are very pure directly following the
synthesis. Anomeric selectivities follow the trends observed in
preliminary studies with the a anomer dominating with ratios of
typically 3 : 1. It is interesting to note that significantly more b
mannoside is produced using this methodology than observed using
classical approaches. The template or resin must be increasing the
propensity for b glycoside formation. Our preliminary results
showed higher a selectivity in the synthesis of the Glc(1,4)Glc
disaccharide on a slightly different template.2 Experiments to
understand the origins of these selectivities are in progress.
In summary, we have successfully exploited the efficiency of
peptide templated glycoside synthesis to prepare a 12 member
library of disaccharides. Our method differs from existing ap-
proaches to parallel saccharide synthesis in that it uses a peptide
coupling, rather than a glycosidation, as the diversity introducing
step.9,10 As a result simple procedures can be followed and, even
without complex automation, the simplicity of the protocols
enabled the library to be prepared in only 4 days.
3 For an alternative approach to peptide templated saccharide synthesis
see: R. J. Tennant-Eyles, B. G. Davis and A. J. Fairbanks, Chem.
Commun., 1999, 1037; R. J. Tennant-Eyles, B. G. Davis and A. J.
Fairbanks, Tetrahedron: Asymmetry, 2000, 11, 231; R. J. Tennant-
Eyles, B. G. Davis and A. J. Fairbanks, Tetrahedron: Asymmetry, 2000,
11, 231; R. J. Tennant-Eyles, B. G. Davis and A. J. Fairbanks,
Tetrahedron: Asymmetry, 2003, 14, 1201.
4 Non-peptide tethers have been used by several groups to control the
regio- and stereoselectivity of glycosidation reactions. For example: F.
Barresi and O. Hindsgaul, J. Am. Chem. Soc., 1991, 113, 9376; M. Bols,
J. Chem. Soc., Chem. Commun., 1992, 913; S. Valverde, A. M. Gomez,
A. Hernandez, B. Herradon and J. C. Lopez, J. Chem. Soc., Chem.
Commun., 1995, 2005; T. Ziegler, G. Lemanski and J. Hurttlen,
Tetrahedron Lett., 2001, 42, 569; M. Müller U. Huchel, A. Geyer and R.
R. Schmidt, J. Org. Chem., 1999, 64, 6190.
5 A. K. Ray and N. Roy, Carbohydr. Res., 1990, 196, 95.
6 H. Franzyk, M. Meldal, H. Paulson and K. Bock, J. Chem. Soc., Perkin
Trans. 1, 1995, 2883.
7 S. V. Ley, D. K. Baeschlin, D. J. Dixon, A. C. Foster, S. J. Ince, H. W.
M. Priepke and D. J. Reynolds, Chem. Rev., 2001, 101, 53; J. L.
Montchamp, F. Tian, M. E. Hart and J. W. Frost, J. Org. Chem., 1996,
61, 3897; U. Berens, D. Leckel and S. C. Oepen, J. Org. Chem., 1995,
60, 8204.
8 Fmoc Solid Phase Peptide Synthesis, A Practical Approach, ed. W. C.
Chan and P. White, Oxford Univeristy Press, Oxford, New York,
2000.
We thank GlaxoSmithKline and the University of Leeds for
helping to fund this work.
9 R. Liang, L. Yan, J. Loebach, M. Ge, Y. Uozumi, K. Sekanina, N.
Horan, J. Gildersleeve, C. Thompson, A. Smith, K. Biswas, W. C. Still
and D. Khane, Science, 1996, 274, 3053; T. Zhu and G-J, Boons, Angew.
Chem., Int. Ed., 1998, 37, 1898.
Notes and references
1 H. M. I. Osborn and T. H. Khan, Tetrahedron, 1999, 55, 1807; P. H.
Seeberger, Chem. Commun., 2003, 1115.
10 Solid Support Oligosaccharide Synthesis and Combinatorial Carbohy-
drate Libraries, ed. P. H. Seeberger, Wiley, New York, 2001.
C h e m . C o m m u n . , 2 0 0 4 , 4 5 4 – 4 5 5
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