A versatile synthetic approach toward diversity libraries using monosaccharide scaffolds

Article abstract of DOI:10.1021/jo9021919

(Chemical Equation Presented) The pyranose scaffold is unique in its ability to position pharmacophore substituents in various ways in 3D space, and unique pharmacophore scanning libraries could be envisaged that focus on scanning topography rather than diversity in the type of substituents. Approaches have been described that make use of amine and acid functionalities on the pyranose scaffolds to append substituents, and this has enabled the generation of libraries of significant structural diversity. Our general aim was to generate libraries of pyranose-based drug-like mimetics, where the substituents are held close to the scaffold, in order to obtain molecules with better defined positions for the pharmacophore substituents. Here we describe the development of a versatile synthetic route toward peptide mimetics build on 2-amino pyranose scaffolds. The method allows introduction of a wide range of substituent types, it is regio- and stereospecific, and the later diversity steps are performed on solid phase. Further, the same process was applied on glucose and allose scaffolds, in the exemplified cases, and is likely adaptable to other pyranose building blocks. The methods developed in this work give access to molecules that position the three selected binding elements in various 3D orientations on a pyranose scaffold and have been applied for the production of a systematically diverse library of several hundred monosaccharide-based mimetics.

Full text of DOI:10.1021/jo9021919

pubs.acs.org/joc
A Versatile Synthetic Approach toward Diversity Libraries using
Monosaccharide Scaffolds
Giang Le Thanh, Giovanni Abbenante, George Adamson, Bernd Becker, Chris Clark,
Glenn Condie, Tania Falzun, Matthias Grathwohl, Praveer Gupta, Michael Hanson,
Ngoc Huynh, Peter Katavic, Krystle Kuipers, Ann Lam, Ligong Liu, Maretta Mann,
Jeff Mason, Declan McKeveney, Craig Muldoon, Andrew Pearson, Premraj Rajaratnam,
Sarah Ryan, Gerry Tometzki, Geraldine Verquin, Jennifer Waanders, Michael West,
Neil Wilcox, Norbert Wimmer, Annika Yau, Johannes Zuegg, and Wim Meutermans*
Alchemia Ltd., Eight Mile Plains, Queensland 4113, Australia
wmeutermans@alchemia.com.au
Received October 12, 2009
The pyranose scaffold is unique in its ability to position pharmacophore substituents in various ways
in 3D space, and unique pharmacophore scanning libraries could be envisaged that focus on scanning
topography rather than diversity in the type of substituents. Approaches have been described that
make use of amine and acid functionalities on the pyranose scaffolds to append substituents, and this
has enabled the generation of libraries of significant structural diversity. Our general aim was to
generate libraries of pyranose-based drug-like mimetics, where the substituents are held close to the
scaffold, in order to obtain molecules with better defined positions for the pharmacophore
substituents. Here we describe the development of a versatile synthetic route toward peptide mimetics
build on 2-amino pyranose scaffolds. The method allows introduction of a wide range of substituent
types, it is regio- and stereospecific, and the later diversity steps are performed on solid phase.
Further, the same process was applied on glucose and allose scaffolds, in the exemplified cases, and is
likely adaptable to other pyranose building blocks. The methods developed in this work give access to
molecules that position the three selected binding elements in various 3D orientations on a pyranose
scaffold and have been applied for the production of a systematically diverse library of several
hundred monosaccharide-based mimetics.
Introduction
The principle of using the monosaccharide scaffold for
peptide-mimetic design was pioneered by Hirschmann and
collaborators1 in the early 1990s and has been exploited over
the past 2 decades.2,3 Several groups have developed solid-
phase and solution-phase approaches in the development of
monosaccharide-based drug discovery libraries.4,5
The pyranose scaffold offers unique opportunities for
drug discovery in terms of positioning pharmacophore
groups in 3D space. The presence of five functionalized
chiral centers provides chemically accessible attachment
points to append target-binding substituents. Altering a
chiral center or position of one substituent results in a
different spatial presentation of the binding elements, on
the same scaffold.
(2) Meutermans, W.; Le, G. T.; Becker, B. ChemMedChem 2006, 1, 1164–
1194.
(3) Schweizer, F.; Hindsgaul, O. Curr. Opin. Chem. Biol. 1999, 3, 291–298.
(4) Hunger, U.; Ohnsmann, J.; Kunz, H. Angew. Chem., Int. Ed. 2004, 43,
1104–1107.
(1) Hirschmann, R.; Nicalou, K. C.; Pietranico, S.; Salvino, J.; Leahy,
E. M.; Sprngeler, P. A.; Furst, G.; Amos B. Smith, I. J. Am. Chem. Soc. 1992,
114, 9217–9218.
(5) Jain, R.; Kamau, M.; Wang, C.; Ippolito, R.; Wang, H.; Dulina, R.;
Anderson, J.; Gange, D.; Sofia, M. J. Bioorg. Med. Chem. Lett. 2003, 13,
2185–2189.
DOI: 10.1021/jo9021919
r
Published on Web 12/07/2009
J. Org. Chem. 2010, 75, 197–203 197
2009 American Chemical Society

Thanh et al.
JOCArticle
For some time now we have been interested in evaluating
the use of the pyranose scaffold in creating a systematic
diversity library of drug-like peptide mimetics, by building
on its unique 3D characteristics and by combining systematic
geometrical diversity with systematic functional diversity.6
Previously described methods do not serve our purpose, as
we wish to generate diverse libraries of products that are
more drug-like and more rigid, i.e., not using amino acids as
the substituents themselves5 and not using carbamates as
linkage functionalities to append the substituents to the core
scaffold.4 Screening of such libraries would not only deliver
pharmacophore information in terms of a combination of
binding elements (substituent motif) and their relative posi-
tioning in space (topography, 3D-presentation) but would
also help identify drug-like hits that can directly enter lead
optimization programs. The methods described in this paper
have been applied in the production of such a geometrically
diverse library containing several hundred monosaccharide-
based mimetics of one substituent motif, which helped
identify hits for many G-protein-coupled receptors recogniz-
ing that motif. The library and the biological results will be
described elsewhere. Here we wish to disclose the synthetic
details that allowed the library production.
Our aim was to establish a versatile synthetic route toward
peptide mimetics 2, where 3 out of R1-R5 carry “binding”
substituents. The synthetic process should allow for multiple
substitution patterns on multiple scaffolds to be generated
simultaneously in one library and should allow a broad range
of substituents to be included in the library. The synthetic
route would have the following properties: (a) compatible to
solid-phase library production; (b) versatile, chemical route
compatible with a wide range of substituents; (c) enabling the
positioning of three pharmacophore subtituents close to the
core scaffold; (d) convergent-creating diversity at the later
stages in the synthetic process.
The most challenging of these with regards to the mono-
saccharide scaffold is to maintain versatility in a regiospecific
synthetic route, given the five functionalized centers. In this
paper we report the development of a versatile and practical
solid-phase synthetic route applied on two monosaccharide
scaffolds, which has enabled us to generate libraries of high
geometrical and functional diversity.
For a multistep solid-phase library process to be success-
ful, each step in the synthesis needs to proceed in high yields
with high purity, without premature cleavage of intermedi-
ates off the resin. Further, as we are aiming to apply the
strategy in the development of diversity libraries, synthetic
versatility is critical for success. We opted to use 2-amino-
glycopyranosides as the core building blocks. The use of the
amine functionality at position 2, rather then the typical
oxygen, simplifies the protecting group strategy and allows
for using the high-yielding and versatile amide bond forma-
tion at one position of the scaffold. Second, we planned to
use ether bonds to link substituents at oxygen positions,
rather than the carbamate bond used in other strategies,4,7,8
in order to increase drug-likeness in the design of our
FIGURE 1. Protected building blocks as starting materials;
TBDPS = tert-butyldiphenylsilyl.
molecules. This requires nucleophilic substitutions and
strong basic reaction conditions, and therefore ether bonds
will need to be established prior to amide bond formation
and the amine protecting group will need to be stable to the
strong basic alkylating conditions. The carbamate-based
protecting groups are therefore precluded; however, the
azide protecting group is practical and suitable for this
purpose. Further, a resin-linkage position and functionality
needs to be selected on the core scaffold for resin attachment.
The cleavage chemistry for this linkage position should be
robust (independent of selection of substituents) and highly
selective and should allow removal of secondary protecting
groups on the substituents. The p-methoxybenzyl ether link9
represents a highly inert bond, which is labile only to oxidiz-
ing or acidic conditions. Alcohols are loaded using the
readily available trichloroacetimidate resin (TCA resin)
and typical TCA-donor promotors. As we aim to introduce
three binding elements on a scaffold with four attachment
positions (not counting the resin-linkage position), we plan
to cap the remaining attachment position with a methyl
group.
The building blocks 1a and 1b (Figure 1) are suited to our
needs.10 The thio-glycoside is stable to many reaction con-
ditions but at the same time is an excellent and versatile
donor,11 which enables introduction of a variety of anomeric
substituents.
Results and Discussion
Step 1. Anomeric Substituent and Loading on Resin. We
opted to introduce the anomeric substituents prior to loading
on resin. This avoids the issue of achieving high stereoselec-
tivity and yield for an on-resin glycosylation. In Scheme 1,
the glycosyl donor 1a was reacted with 2-phenyl-ethanol 3
using the thiophilic reagent dimethyl(methylthio)sulfonium
triflate (DMTST) as the glycosyl promoter, in the presence of
molecular sieves. The glycosylation gave anomers 4a and 4b
in a 1:1 anomeric ratio, which were readily separated on
standard column chromatography.
An excess of the R-anomer 4a (3 equiv to the resin-bound
trichloro acetimidate) was loaded onto the resin via the
4-hydroxy position using BF3 3 Et2O as promoter. After
completion, a resin loading was determined by HPLC ana-
lysis of a cleavage solution from a known weight of resin 5a
against a reference standard curve for compound 4a. The
(9) Hanessian, S.; Xie, F. Tetrahedron Lett. 1998, 39, 733–736.
(10) Rajaratnam, P.; Gupta, P.; Katavic, P.; Kuipers, K.; Huyh, N.;
Ryan, S.; Falzun, T.; Tometzki, G.; Bornaghi, L.; Thanh Le, G.; Abbenante,
G.; Liu, L.; Meutermans, W.; Wimmer, N.; West, M. Aust. J. Chem. 2009,
accepted for publication.
(11) Oscarson, S. In Carbohydrates in Chemistry and Biology; Beat Ernst,
G. W. H., Pierre Sinay, Eds.; Wiley-VCH Verlag GmbH: Weinheim, 2000;
Vol. 1, pp 93-116.
(6) Thanh le, G. A., G; Becker, B; Grathwohl, M; Halliday, J; Tometzki,
G; Zuegg, J; Meutermans, W. Drug Discovery Today 2003, 8, 701–709.
(7) Wunberg, T.; Kallus, C.; Opatz, T.; Henke, S.; Schmidt, W.; Kunz, H.
Angew. Chem., Int. Ed. 1998, 37, 2503–2505.
(8) Kallus, C.; Opatz, T.; Wunberg, T.; Schmidt, W.; Henke, S.; Kunz, H.
Tetrahedron Lett. 1999, 40, 7783–7786.
198 J. Org. Chem. Vol. 75, No. 1, 2010

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SCHEME 1. Glycosylation and Resin Loading Steps
SCHEME 2. Introduction of R3
SCHEME 3. Introduction of R5
excess R-glucopyranoside 4a could be recovered from the
DCM solution through a simple washing process with brine,
and the recovered glucopyranoside 4a could be reused in
additional loading reaction. Similar loading of the β-anomer
4b provided resin 5b.
sequence was repeated 3 times, to drive the reaction to
product 8a to completion.
Step 3. Introduction of R5 (Scheme 3). Removal of the tert-
butyldiphenylsilyl (TBDPS) protecting group to the free
alcohol 9a can be achieved using HF-pyridine solution. How-
ever, as we were planning to adapt the solid-phase chemistry
to library synthesis using ceramic 2D bar-coded mini-Kans,
we decided to look for a different method that is less prone to
etching. For this reason we prepared a proton sponge/HF salt
Step 2. Introduction of R3. To introduce the R3 substituent
ꢀ
(scheme 2), the resin 5a was first subjected to Zemplen O-
deacylation conditions for removal of the benzoate protect-
ing group.12 Subsequent alkylation of the free hydroxyl
group in product 6a with 2-bromomethyl naphthalene 7
was examined using various reagents and reaction condi-
tions.
(PS HF) by simply mixing an HF-pyridine solution with a
3
THF solution of proton sponge. The PS HF salt precipitates
3
out as a white solid and can be weighed out to create accurate
concentrationsofthe HFsalt fordeprotection. Weestablished
suitable conditions for complete and clean removal of the
In our initial attempts we used KOtBu as a base but could not
achieve alkylation in good yield (maximum of 25%). Although
different solvents (THF, DMF), additives (crown ether, TBAI),
concentrations, and order of addition of reagents were tested,
the yield of the alkylation remained lower than 25%. Subse-
quently we found that if LiCl was added to the reaction, the
yields improved dramatically (up to 90% after 48 h alkylation).
One possible explanation for this observation is that a smaller
Liþ cation may be able to stabilize the alkoxide better in a
polystyrene resin environment.
TBDPS group, using a PS HF solution (0.5N in DMF with
3
5% acetic acid) at 65 °C overnight. These conditions do
not etch glass or ceramic 2D barcodes and thus reac-
tions can be carried out in standard glassware. The PS HF
3
salt and its use in halogen exchange reactions have been des-
cribed earlier,13 though to our knowledge its use in removing
silyl-based protecting groups has not been reported before.
Following complete removal of TBDPS, the alkylation
process was carried out as described using MeI as the halide
to generate the intermediate 10a.
Best results were obtained when the resin was pretreated
with a LiOtBu /DMF solution for 20 min, then drained, and
immediately treated with bromide in DMF. This reaction
^
(13) Darabantu, M.; Lequeux, T.; Pommelet, J. C.; Pleab, N.; Turckb, A.
Tetrahedron 2001, 57, 739–750.
(12) Zemplen, G. 1927, 60, 1555.
J. Org. Chem. Vol. 75, No. 1, 2010 199

Thanh et al.
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FIGURE 2. Representative examples of final compounds.
SCHEME 4. Introduction of R2
SCHEME 5. Production of Naphtyl Glycosides 4c and 4d
Step 4. Introduction of R2 and Cleavage off Resin
(Scheme 4). The azide function at position 2 of compound
10a was reduced to the free amine using DTT under basic
conditions. The resulting amine was then acylated using
HBTU preactivated acid 11 in DMF, to form product 12a.
Finally, the product 2a was cleaved off the resin using a
10% TFA solution in DCM, with 20% triethylsilane as
scavenger.
Representative Examples. Having established a functional
solid-phase approach, we wanted to evaluate the robustness
of this approach by further synthesizing additional examples
2b-e (figure 2).
Product 2b is the β-anomer of compound 2a and demon-
strates anomeric integrity in the process. Product 2c carries
other amino acid side chain substituents (guanidine and
phenol) and serves to demonstrate the functional versatility
of the approach. Compounds 2d and 2e have substitution
patterns different from that of 2a and help demonstrate the
ability to create structurally diverse molecules. Compound 2e
further illustrates theapplicationonthe allosescaffold and the
stability of the thiomethyl anomeric substituent to the syn-
thetic approach. The solid-phase synthesis and list of reagents
for products 2a-e are summarized in Scheme 6 and Table 1.
The synthesis of compound 2b starts off with the β-anomer
4b and follows the identical synthetic route as for the R-
anomer 4a. The product 2b is obtained in good yield and high
purity following this solid-phase process. The results demon-
strate that the anomeric substituent is stable to the acidic
cleavage conditions.
Separation of anomers 4c and 4d and loading on resin
provides starting resins 5 for the solid-phase synthetic pro-
cess (Scheme 6) using reactants as outlined in Table 1.
Specifically for compound 2c, the phenol functionality is
introduced through alkylation with (3-tert-butoxy-phenyl)-
methyl bromide 17, prepared from commercially available
(3-tert-butoxy-phenyl)methanol. The tert-butyl protecting
group is effectively removed under the TFA cleavage condi-
tions to produce the free phenol 2c.
Fmoc-protected amino acids 20 and 19 were used for both
target compounds 2c and 2d, respectively. Following acyla-
tion, the Fmoc protecting group was removed by treatment
with piperidine. The guanidine functionality was then intro-
duced on solid phase14 from the free amine 14 with 3,5-
dimethyl-1-pyrazolylformamidinium nitrate (DMPFN) 15
to afford the resin-bound guanidinylated compounds 16.
TFA-induced cleavage and HPLC purification provided the
fully unprotected guanidines 2c and 2d.
Synthesis of the allose molecule 2e proceeds in the same
way as for the glucose products, following loading of the
allose building block 1b on resin. Loading and introduction
of the R3 substituent is slower at the axial allose position,
when compared to the equatorial glucose position but still
proceeds to completion after 3-5 alkylation cycles.
Experimental Section
Glycosylation of Glc-SMe with Phenyl Ethanol 3. Building
block 1a (Glc-SMe) (40.0 gr, 0.069 mol) and phenyl ethanol
3 (41.5 mL, 0.346 mol, 5 equiv) were dissolved in dry DCM
The synthetic route toward guanidines 2c and 2d starts off
with a glycosylation of the glucose building block 1a with
naphtyl-2-methanol 13 (Scheme 5).
(14) Sulyok, G. A.; Gibson, C.; Goodman, S. L.; Holzemann, G.;
Wiesner, M.; Kessler, H. J. Med. Chem. 2001, 44, 1938–50.
200 J. Org. Chem. Vol. 75, No. 1, 2010

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SCHEME 6. Synthetic Route toward Representative Examples 2a-e
TABLE 1. Reactants per Synthetic Steps 1-4 for Products 2a-e
representative examples
solution was washed with distilled water (500 mL). The water
layer was re-extracted with DCM (3 ꢀ 100 mL). All organic
layers are combined, dried (MgSO4), filtered, and evaporated to
dryness. The anomers 4a and 4b were separated and purified
directly from this residue by FC (PE/EtOAc 10:1 to 1:10).
(2-Phenethyl)-2-azido-3-O-benzoyl-6-O-(tert-butyldiphenyl-
silyl)-2-deoxy-1-(2-phenethyl)-r-D-glucopyranoside (4a). After
FC purification, the title compound was obtained as a white
solid (17.6 gr, 39%): Rf (PE/DCM 1:5) = 0.59; 1H NMR (400
MHz, CDCl3) δ 1.06 (s, 9H, CH3), 2.94-3.03 (m, 2H, OCH2-
CH2Ar), 3.32 (ddd, 1H, JH2,H3 = 10.6 Hz, H-2), 3.41-3.46
(ddd, 1H, H-5), 3.73-3.90 (m, 4H, OCH2(B), H-4, H-6a, H-6b),
3.90 (m, 1H, OCH2(A)), 5.00 (d, 1H, JH1,H2 = 3.3 Hz, H-1), 5.54
stepa
1
2a
1a
2b
1a
2c
1a
2d
1a
2e
1b
BBb
R-OH
productc
RLd
R-Br
R-Br
R-CO2H
3
3
13
4c
0.35
17
MeI
20
13
4d
0.37
MeI
8
4a
0.45
7
MeI
11
4b
0.37
7
MeI
11
1b
0.32
7
18
21
2
3
4
19
aRefers to the synthetic steps 1-4 in the process as described in the
text. bBB means building block. cRefers to the productfrom the solution-
phase glycosylation (see Schemes 1 and 5). dResin loading of the BB,
expressed in mmol/gr.
(dd, 1H, JH3,H4 = 9.4 Hz, H-3), 7.18-8.13 (m, 20 H, HAr); 13
C
NMR (100.6 MHz, CDCl3) δ 19.3, 26.8, 36.0, 61.1, 63.8, 68.7,
70.8, 71.7, 74.0, 97.6, 126.4, 127.69, 127.71, 128.42, 128.43,
129.1, 129.4, 129.78, 129.79, 130.0, 133.08, 133.09, 133.4,
135.59, 135.62, 138.4, 167.0. MS (ES) m/z = 674.1 [M þ Na];
HRMS (ESI, pos mode) m/z [M þ Na]þ calcd for C37H41N3O6Si
674.2657; found 674.2651.
(2-Phenethyl)-2-azido-3-O-benzoyl-6-O-(tert-butyldiphenyl-
silyl)-2-deoxy-1-(2-phenethyl)-β-D-glucopyranoside (4b). After
FC purification, the title compound was obtained as a white
solid (14.4 gr, 32%): Rf (PE/DCM 1:5) = 0.43; 1H NMR (400
MHz, CDCl3) δ 1.06 (s, 9H, CH3), 2.99 (t, 2H, J = 7.2. Hz,
OCH2CH2Ar), 3.47 (ddd, 1H, H-5), 3.58 (ddd, 1H, JH1,H2 = 8.0
Hz, JH2,H3 = 10.2 Hz, H-2), 3.77-3.83 (m, 1H, OCH2(B)), 3.86
(t, 1H, H-4), 3.96 (d, 2H, J = 4.6 Hz, H-6a, H-6b), 4.10-4.16
(m, 1H, OCH2(A)), 4.46 (d, 1H, H-1), 5.07 (dd, 1H, JH3,H4 = 9.4
Hz, H-3), 7.18-8.13 (m, 20 H, HAr); 13C NMR (100.6 MHz,
CDCl3) δ 19.3, 26.8, 36.2, 64.0, 64.2, 70.80, 70.88, 75.40, 76.45,
101.9, 126.4, 127.76, 127.80, 128.42, 128.50, 128.90, 129.29,
129.86, 130.04, 132.88, 132.99, 133.55, 135.57, 135.66, 138.19,
166.9; MS (ES) m/z [M þ Na] = 674.1; HRMS (ESI, pos mode)
m/z [M þ Na]þ calcd for C37H41N3O6Si 674.2657; found
674.2655.
(640 mL), and the mixture was stirred over molecular sieves
(AW300, previously dried at 300 °C) under N2. After 1 h a
solution of DMTST (44.7 gr, 0.173 mol, 2.5 equiv) in dry DCM
(346 mL) was added to the building block 1a and alcohol
mixture and stirred under N2 at rt; evolution of reaction was
checked by TLC and LC/MS. After complete reaction of
starting material (1-3 h), the reaction mixture was filtered on
Celite and washed with DCM (1 L). The organic phase was
washed with a saturated NaHCO3 solution (3 ꢀ 1.6 L). The
aqueous phase was re-extracted with DCM (200 mL). The
combined organic phases were dried (MgSO4), filtered, and
evaporated under reduced pressure to afford a crude residue,
which contained desired R/β anomers in both TBDPS-protected
and unprotected form. To reprotect the 6-position with the
TBDPS group, this crude material was treated with imidazole
(3.83 gr, 0.056 mol)) and TBDPS-Cl (8.65 mL, 0.034 mol) in dry
DMF (50 mL). The mixture was stirred under N2 at rt for 2 h.
The reaction mixture was diluted with EtOAc (500 mL), and the
Glycosylation of Glc-SMe with 2-Napthalene Methanol.
GlcSMe (1a) (37.0 g, 64.0 mmol) and 2-napthalene methanol
(40.5 g, 256.2 mmol) were used in the glycosylation as described
above. The crude material was purified by FC using EtOAc/PE
(1:19-1:9) as eluent to give the R-anomer 4c (12.12 g, 27%) and
the β-anomer 4d (8.32 g, 19%).
(20-Napthylmethyl)-2-azido-3-O-benzoyl-6-O-(tert-butyldiphe-
nylsilyl)-2-deoxy-1-r-D-glucopyranoside (4c). After FC purifica-
tion, title compound was obtained as a white solid (12.12 g,
J. Org. Chem. Vol. 75, No. 1, 2010 201

Thanh et al.
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27%): Rf TLC (DCM) = 0.78 ; 1H NMR (400 MHz, CDCl3) δ
1.10 (s, 9H, CH3), 3.41 (dd, 1H, JH2,H3 = 10.6 Hz H-2), 3.87 (t,
1H, JH4,H5 = 9.2 Hz, H-4), 3.90-3.99 (m, 3H, H-5, H-6a, H-6b),
4.76 (d, 1H, OCH2(B)), 4.94 (d, 1H, JA,B = -11.9 Hz, OCH2-
was gently shaken for 20 min at rt, and the resin was filtered off.
This stepwise process of LiOtBu and alkylating agent treatment
was performed 5 times, using fresh LiOtBu solution and fresh
alkylating agent solution. The resin was finally washed with
DMF (ꢀ3, each 4 mL), MeOH (ꢀ3, each 4 mL), and DCM (ꢀ3,
each 4 mL).
(A)), 5.11 (d, 1H, JH1,H2 = 3.5 Hz, H-1), 5.66 (dd, 1H, JH3,H4
=
8.9 Hz, H-3), 7.36-8.14 (m, 22H, HAr); 13C NMR (100.6 MHz,
CDCl3) δ 19.3, 26.9, 61.2, 63.9, 69.4, 70.9, 72.1, 74.3, 96.4, 125.8,
126.1, 126.2, 127.2, 127.70, 127.74, 127.76, 127.96, 128.39,
128.45, 129.32 129.8, 130.0, 133.09, 133.12, 133.16, 133.18,
133.5, 133.8, 135.62, 135.67, 167.1; MS (ES) m/z 710.1 [M þ
Na]; HRMS (ESI, pos mode) m/z [M þ Na]þ calcd for
C40H41N3O6Si 710.2657; found 710.2649.
(20-Napthylmethyl)-2-azido-3-O-benzoyl-6-O-(tert-butyldiphe-
nylilyl)-2-deoxy-1-β-D-glucopyranoside (4d). After FC purifica-
tion, the title compound was obtained as a white solid (8.32 g,
19%): Rf TLC (DCM) = 0.67 ; 1H NMR (400 MHz, CDCl3) δ
Preparation of PS HF reagent. Proton sponge (4.8 g; 22.4
3
mmol) was dissolved in THF (30 mL) in a plastic vessel.
HF pyridine solution was slowly added dropwise until no
3
precipitation occurred (ca. 1.2 mL). The precipitated white solid
was filtered under N2, washed with THF (ꢀ2, each 5 mL) and
ether (ꢀ3, each 10 mL), and dried in the vacuum oven over P2O5
for 24 h (5.03 g; 96%). This material was prepared fresh each
time and used without further purification in the TBDPS
deprotection step.
TBDPS Deprotection at O-6. A solution of 0.5 M PS HF and
3
1.10 (s, 9H, CH3), 3.50 (ddd, 1H, H-5), 3.69 (dd, 1H, JH2,H3
=
AcOH 5% in dry DMF (5 mL) was added to the resin and stirred
and heated at 65 °C for 24 h. After cooling down, the solution
was aspirated, and the resin was washed with DMF (ꢀ3, each 4
mL), THF (ꢀ3, each 4 mL), and DCM (ꢀ3, each 4 mL).
Azide Reduction. A dry DMF solution of 0.2 M LiOtBu and
0.2 M DTT was prepared, the solution (5 mL) was added to the
resin, and the resin was gently shaken for 24 h (vortex) at rt. The
solution was then aspirated, and the resin was washed with
DMF (ꢀ3, each 4 mL), MeOH (ꢀ3, each 4 mL), and DCM (ꢀ3,
each 4 mL) and dried under N2.
10.2 Hz H-2), 3.89 (t, 1H, JH4,H5 = 9.9 Hz, H-4), 3.99-4.05 (m,
2H, H-6a, H-6b), 4.56 (d, 1H, JH1,H2 = 8.0 Hz, H-1), 4.86 (d,
1H, OCH2(B)), 5.06 (dd, 1H, JH3,H4 = 9.4 Hz, H-3), 5.10 (d, 1H,
JA,B = -11.9 Hz,OCH2(A)), 7.37-8.13 (m, 22H, HAr); 13C
NMR (100.6 MHz, CDCl3) δ 19.3, 26.9, 64.05, 64.14, 70.76,
70.99, 75.6, 76.6, 100.3, 125.8, 126.1, 126.2, 127.0, 127.70,
127.77, 127.81, 127.95, 128.37, 128.48, 129.22 129.87, 129.88,
130.0, 132.9, 133.07, 133.15, 133.22, 133.6, 133.97, 135.6, 135.7,
167.0; MS (ES) m/z 710.1 [M þ Na]; HRMS (ESI, pos mode) m/z
[M þ Na]þ calcd for C40H41N3O6Si 710.2657; found 710.2661.
General Solid-Phase Procedures. Resin Loading. TCA-Wang
resin (1 g, 1.08 mmol/g) and glycosides 1b and 4a-d (3 mmol)
were dried under high vacuum over KOH overnight before use.
In the glovebox, each glycoside was dissolved in anhydrous
DCM (8 mL). Then the resin was washed with dry THF (10 mL)
followed by dry DCM (ꢀ2, each 10 mL), the glycoside solution
was added to the resin, and the mixture was shaken for 2 min.
Acylation at N2. A solution of HBTU 0.5 M in dry DMF was
prepared. The acid (2 mmol) was dissolved in dry DMF (4 mL),
and HBTU solution (4 mL) was added. DIPEA (0.7 mL, 4
mmol). The resulting mixture was swirled and allowed to stand
for 10 min. The solution was added to the resin at room
temperature and was gently shaken for 24 h. The solution was
then aspirated and the resin washed with DMF (ꢀ3, each 4 mL),
MeOH (ꢀ3, each 4 mL) and DCM (ꢀ3, each 4 mL) and dried
under N2.
Fmoc Deprotection. (Only for products 2c and 2d.) A solution
of piperidine in dry DMF (1:5 ; 5 mL) was added to the resin.
The mixture was gently shaken (vortex) for 2 h at rt. The
solution was then aspirated, and the resin was washed with
DMF (ꢀ3, each 4 mL), MeOH (ꢀ3, each 4 mL), and DCM (ꢀ3,
each 4 mL) and dried under N2.
Formation of Guanidine. (Only for products 2c and 2d.) A
solution of 0.25 M DMPFN 15 and 1 M DIPEA in dry DMF
was added to the resin. The mixture was stirred and heated at
65 °C overnight. After cooling down, the solution was aspirated,
and the resin was washed with DMF, MeOH, and DCM (3 times
each).
Cleavage off Resin. The resin was treated with cleavage
solution (TFA/TES/dry DCM 10/20/70, 1 mL) for 3 h at rt.
The cleavage solution was then drained, and the resin was
washed with THF, DCM, and THF (1 mL each). The solvents
were evaporated to obtain crude cleavage product.
NH3 Treatment. The crude cleavage product from the clea-
vage step was treated with freshly prepared saturated ammonia
solution in MeOH (2 mL). The solution was gently shaken and
left to stand for 2 h at room temperature. The solution was
evaporated, and crude samples were purified by LCMS on a
standard C18 column using gradient programs of acetonitrile
and water.
(2-Phenethyl)-2-(40-aminobutyrylamido)-2-deoxy-6-O-methyl-
3-O-(20-napthylmethyl)-r-D-glucopyranoside (2a). Resin loaded
glycoside 4a (80 mg resin, 0.45 mmol/g) was carried through the
solid-phase synthetic process. The title product was isolated by
HPLC purification and MS detection as a white solid (8.7 mg,
46% over 7 steps): 1H NMR (400 MHz, CDCl3) δ 1.45-1.56 (m,
2H, NHCOCH2CH2CH2NH2), 1.79-1.92 (m, 2H, NHCOCH2-
CH2CH2NH2), 2.51 (t, 2H, J = 6.9 Hz, NHCOCH2CH2CH2-
NH2), 2.85 (dd, 2H, J = 6.7 Hz, OCH2CH2Ph), 3.39 (s, 3H,
BF3 Et2O (0.3 mmol) was then added, and the mixture was
3
shaken for 10 min. After that, additional BF3 Et2O (0.3 mmol)
3
was added, and the resin mixture was shaken for 10 min,
drained, and washed with dry DCM (ꢀ5, each 10 mL) to recover
the glycoside. The combined DCM with unreacted glycoside
was washed with saturated NaHCO3 (ꢀ3, each 20 mL) solution,
dried (MgSO4), and evaporated under reduced pressure. Finally
the resin was washed with dry THF (ꢀ4, each 10 mL) and dry
DCM (ꢀ4, each 10 mL) and dried under high vacuum overnight.
Resin Loading Determination. The glycoside-resin was dried
under high vacuum for a minimum of 16 h. Anhydrous DCM/
triethylsilane (TES)/trifluoroacetic acid (TFA) (7:2:1) was pre-
pared under N2. About 70 mg of the dried loaded resin was then
weighed into a 4.5 mL reaction tube, and the cleavage solution (1
mL) was added. After the top of the tube was sealed with a white
plastic cap, the cleavage reaction was left at rt for 2-3 h, then
filtered, and washed with DCM (ꢀ4, each 2 mL), and the
filtrates were combined and diluted to a known volume. The
concentration of the desired glycoside was then determined
using HPLC/C18 chromatography comparison against a stan-
dard curve obtained from five known glycoside concentrations
(ranging from 0.06 to 1.2 mg/mL).
Benzoate Removal at O-3. NaOMe solution (40 mM in THF/
MeOH 5:1) was added to the resin (80 mg) under N2 and was
gently shaken overnight (vortex). The reaction solution was
filtered, and the resin was washed with THF/AcOH/MeOH
(8:1:1, ꢀ3, each 4 mL), THF (ꢀ3, each 4 mL), and DCM (ꢀ3,
each 4 mL) and dried on high vacuum overnight.
Alkylation (O-3 and O-6). A solution of LiOtBu in dry DMF
(0.25 M) was prepared, as well as a solution of alkylating agent
in dry DMF (0.25 M). The resin was washed with dry DMF
(4 mL) and then treated with the LiOtBu solution (2.5 mL) for
10 min at room temperature. The LiOtBu solution was removed,
and the alkylating agent solution (2.5 mL) added. The reaction
202 J. Org. Chem. Vol. 75, No. 1, 2010

Thanh et al.
JOCArticle
OCH3), 3.53-3.62 (m, 5H, H3/H5/H6 and one H from
OCH2CH2Ph), 3.73 (dd, 1H, J
(ESI, pos mode) m/z [M þ H]þ calcd for C30H39N4O7 567.2813;
= 8.8 Hz, H4), 3.95 (dt,
found 567.2810.
H3,H4
1H, J = 9.7 Hz, J = 5.8 Hz, one H from OCH2CH2Ph), 4.23
(ddd, 1H, J = 10.5 Hz, J = 9.4 Hz, J = 3.6 Hz, H2), 4.70 (d, 1H,
J = 3.6 Hz, H1), 4.83 (d, 1H, J = 11.9 Hz, one H from OCH2-
Ph), 4.89 (d,1H, J = 11.9 Hz, one H from OCH2Ph), 5.43 (d, 1H,
J = 9.4 Hz, NH), 7.13-7.26 (m, 5H, HAr), 7.42-7.49 (m, 3H,
HAr), 7.77-7.83 (m, 4H, HAr); 13C NMR (100.6 MHz, CDCl3) δ
29.2, 34.2, 36.1, 41.7, 51.8, 59.7, 68.5, 70.4, 71.8, 72.8, 73.6, 80.0,
98.0, 126.3, 126.5, 126.6, 126.9, 127.0, 127.9, 128.1, 128.4, 128.6,
129.1, 133.2, 133.5, 136.1, 139.2, 172.6; HRMS (ESI, pos mode)
m/z [M þ H]þ calcd for C30H39N2O6 523.2803; found 523.2804.
(2-Phenethyl)-2-(40-aminobutyrylamido)-2-deoxy-6-O-meth-
yl-3-O-(20-napthylmethyl)-β-D-glucopyranoside (2b). Resin loa-
ded glycoside 4b (80 mg resin, 0.37 mmol/g) was carried through
the solid-phase synthetic process. The title product was isolated
by HPLC purification and MS detection as a white solid (4.3 mg,
28% over 7 steps): 1H NMR (400 MHz, DMSO-d6) δ 1.56-1.77
(m, 2H, NHCOCH2CH2CH2NH2), 1.99-2.15 (m, 2H, NHCO-
CH2CH2CH2NH2), 2.72-2.95 (m, 2H, NHCOCH2CH2CH2-
NH2), 2.78 (t, J = 6.3 Hz, 2H, OCH2CH2Ph), 3.29 (s, 3H,
OCH3), 3.30-3.37 (m, 2H, H4,H6b), 3.45-3.52(m, 2H, H-3, H-
6a), 3.57-3.69 (m, 3H, H-2, H-5, OCH2(B)CH2-Ph), 3.88 (m,
1H, 1H, OCH2(A)CH2-Ph), 4.41 (d, 1H, JH1,H2 = 8.4 Hz, H-1),
4.73 (d, 1H, JA,B = -11.8 Hz, 1H, OCH2(B)-Naph), 4.92 (d, 1H,
OCH2(A)-Naph), 5.43 (m, 1H, OH-4), 6.69 (bs, 3H, NH3), 7.83
(d, 1H, JNH,H-2 = 8.4 Hz, C-2NH), 7.16-8.00 (m, 12H, Har);
13C NMR (100.6 MHz, DMSO-d6) δ 25.98 (CH2CH2CH2), 33.3
(COCH2), 35.3, (CH2CH2Ph), 40.3, (H2NCH2), 58.4 (OCH3),
68.9 (OCH2CH2Ph), 70.1 (C-4/C-5*), 71.5 (C-6), 73.2
(OCH2Nap), 75.4 (C-4/C-5*), 82.4 (C-3), 100.6 (H-1), 124.1,
125.5, 125.87, 125.88, 125.89, 125.90, 127.3, 127.4, 127.5, 128.00,
128.02, 128.70, 128.72, 132.2, 132.6, 136.6, 138.7 (all aromat. C),
156.9 (TFA), 171.4 (NHCO); HRMS (ESI, pos mode) m/z [M þ
H]þ calcd for C30H39N2O6 523.2803; found 523.2803.
(20-Napthylmethyl)-2-deoxy-2-(30-guanidinopropionylamido)-
3-O-methyl-6-O-(20-napthylmethyl)-β-D-glucopyranoside (2d).
Resin loaded glycoside 4d (80 mg resin, 0.37 mmol/g) was
carried through the solid-phase synthetic process. The title pro-
duct was isolated by HPLC purification and MS detection as a
1
white solid (11.3 mg, 54% over 9 steps): H NMR (400 MHz,
DMSO-d6) δ 2.40 (dq, 2H, COCH2), 3.19,(t, 1H, J H4,H5 = 9.3
Hz, H-5), 3.26-3.43 (m, 7H, OCH3, H-3, H-4, CH2NH2),
3.64-3.72 (m, 2H, H-2, H-6), 3.85 (d, 1H, J
= -10.5
= 8.4 Hz, H-1), 4.72 (d, 3H,
H-6a,6b
Hz, H-6), 4.47 (d, 1H, J
H1,H2
OCH2(A,B)Nap1, OCH2(B)Nap2), 4.91 (d, 1H, J A,B = -12.7
Hz, OCH2(A)Nap2), 5.36 (d, 1H, J = 6.3 Hz, OH-4),
OH,H-4
7.40-7.94 (m, 15H, aromat.H, NHdC), 7.63 (t, 1H, J CH2,NH
5.3 Hz, CH2NH), 8.15 (d, 1H, J NH,H2 = 9.1 Hz, CONH); 13
NMR (100.6 MHz, DMSO-d6) 34.6, (COCH2), 37.0
=
C
δ
(H2NCH2), 53.9 (C-2), 59.1 (OCH3), 69.478 (C-6), 69.482 (C-
4), 69.6 (OCH2Nap), 72.3 (OCH2Nap), 75.6 (C-3), 83.3 (C-5),
100.1 (C-1), 125.57, 125.61, 125.68, 125.70, 125.76, 126.0,
126.03, 127.43, 127.43, 127.52, 127.53, 127.64, 127.67, 132.30,
132.32, 132.60, 132.70, 135.36, 136.21 (all aromat. C), 156.8
(TFA), 158.18, 158.43, (guanidine C), 169.94 (CONH); HRMS
(ESI, pos mode) m/z [M þ H]þ calcd for C33H39N4O6 587.2864;
found 587.2865.
Methyl [2-(30Aminopropionylamido)-6-O-(40-chlorobenzyl)-2-
deoxy-3-(20-napthylmethyl)-1-thio-β-D-allopyranose] (2e). Resin
loaded building block 1b (80 mg resin, 0.32 mmol/g) was carried
through the solid-phase synthetic process. The title product was
isolated by HPLC purification and MS detection as a white solid
(4.1 mg, 29% over 7 steps): 1H NMR (400 MHz, DMSO-d6) δ
2.04 (s, 3H, SCH3), 2.37-2.52 (2 ꢀ td, under DMSO peak,
NHCOCH2CH2NH2), 2.86 (dd, J = 7.0 Hz, 2H, NHCOCH2-
CH2NH2), 3.54-3.59 (m, 2H, H4/H6a), 3.70-3.76 (m, 1H,
JH6a,H6b= -11.0 Hz, JH5,H6b= 1.3 Hz, H6b), 3.82-3.90 (m,
(20-Napthylmethyl)-2-deoxy-2-(40-guanidinobutyrylamido)-3-
O-(30-hydroxybenzyl)-6-O-methyl-r-D-glucopyranoside (2c). Re-
sin loaded glycoside 4c (80 mg resin, 0.35 mmol/g) was carried
through the solid-phase synthetic process. The title product was
isolated by HPLC purification and MS detection as a white solid
(11.0 mg, 58% over 9 steps): 1H NMR (400 MHz, DMSO-d6) δ
1.61-1.68 (m, 2H, NHCOCH2CH2CH2NH2), 2.20 (t, 2H,
J = 7.2. Hz, NHCOCH2CH2CH2NH2), 3.02-3.10 (dq, 2H,
NHCOCH2CH2CH2NH2), 3.31 (s, 3H, OCH3), 3.29 (s, 3H,
OCH3), 3.34-3.39 (m, 1H, H4), 3.52 (dd, 1H, JH5,H6=5.8 Hz,
3H, H2/H3/H5), 4.52 (s, 2H, OCH2Ph4Cl), 4.62 (d, J = 10.3 Hz,
1H, H1), 4.83 (d, J = 11.8 Hz, 1H, one H from OCH2Nap), 4.98
(d, J = 11.8 Hz, 1H, one H from OCH2Nap), 5.33 (bs, 1H, OH,
exchanged in D2O), 7.34-7.40 (m, 4H, aromat. H), 7.46-7.50
(m, 2H, aromat. H), 7.62 (dd, 1H, J = 8.2 Hz, J = 1.5 Hz,
aromat. H), 7.86-7.90 (m, 4H, aromat. H), 8.20 (d, 1H, J = 8.8
Hz, NH, exchanged with D2O); 13C NMR (100.6 MHz, DMSO-
d6) δ 11.8, 32.7, 36.0, 51.8, 68.8, 70.6, 72.1, 75.2, 76.9, 78.7, 81.1,
126.4, 126.7, 126.8, 126.9, 127.0, 128.2, 128.4, 128.9, 129.8, 132.5,
133.1, 133.4, 137.2, 138.4, 169.6; HRMS (ESI, pos mode) m/z [M
þ H]þ calcd for C28H34ClN2O5S 545.1871; found 545.1867.
J
H6a,H6b = -10.7 Hz, H-6), 3.58-3.67 (m, 2H, H-3, H-6), 3.72
(ddd, 1H, H-5), 3.86-3.92 (m, 1H, H-2), 4.57 (d, 1H, JA,B
=
-11.2 Hz, OCH2(B)-Ar1), 4.63 (d, 1H, JA,B=-12.5 Hz, OCH2-
(B)-Ar2), 4.73 (d, 1H, OCH2(A)-Ar1), 4.75 (d, 1H, JH2 = 3.5 Hz,
H-1), 4.84 (d, 1H, OCH2(A)-Ar2), 5.42 (d, 1H, JOH,H-4 = 7.1
Hz, OH-4), 6.63-7.95 (m, 12H, 11 aromat. H, NHdC), 7.68 (bs,
3H, NH3), 8.15 (d, 1H, JNH,H-2 = 8.7 Hz, C-2NH), 9.29 (s, 1H,
Acknowledgment. The authors would like to thank Laur-
ent Bornaghi, Nicholas Drinnan, and Max Broadhurst for
the large-scale synthesis of the initial building blocks 1a and
1b and Chris Warnholtz and Sandy Kong for the analysis/
purification of the representative products.
OH-Ar); 13C NMR (100.6 MHz, DMSO-d6)
δ 24.6
(CH2CH2CH2), 31.7 (COCH2), 40.3 (H2NCH2), 52.3 (C-2),
58.4 (OCH3), 68.2 (OCH2Ar2), 70.4 (C-4), 71.4 (C-6), 71.7 (C-
5), 73.4 (OCH2Ar1), 79.3 (C-3), 96.1 (C-1), 113.8, 114.2, 117.8,
125.83, 125.86, 126.1, 126.2, 127.45, 127.51, 127.7, 128.7, 132.4,
132.6, 135.1, 140.6, (all aromat. C), 156.7, 157.0 (TFA þ TFA-
salt)), 158.21, 158.45, (guanidine C), 171.7 (NHCO); HRMS
Supporting Information Available: Experimental details for
the synthesis of (3-tert-butoxy-phenyl)methyl bromide 17, and
NMR spectral data (1H, 13C and COSY) for compounds 4a-d
and 2a-e. This material is available free of charge via the
Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 1, 2010 203