Novel chemoenzymatic methodology for the regioselective glycine loading on polyhydroxy compounds

Article abstract of DOI:10.1039/b927021c

In the present work, we have developed a highly efficient temperature-dependent chemo-enzymatic methodology for the regioselective synthesis of novel esters of glycerol, G1 tri-glycerol dendrons and related esters for the first time using 4-nitrophenyl 2-(tert-butoxycarbonyl)acetate (Boc-gly-Ph-pNO₂) (2) as the acylating agent. This methodology offers efficient and controlled loading of amino acid (glycine) on polyhydroxy compounds.

Full text of DOI:10.1039/b927021c

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Novel chemoenzymatic methodology for the regioselective glycine loading on
polyhydroxy compounds†
Shashwat Malhotra,a,b Marcelo Caldero´n,b Ashok K. Prasad,a Virinder S. Parmar*a and Rainer Haag*b
Received 23rd December 2009, Accepted 19th February 2010
First published as an Advance Article on the web 11th March 2010
DOI: 10.1039/b927021c
In the present work, we have developed a highly efficient temperature-dependent chemo-enzymatic
methodology for the regioselective synthesis of novel esters of glycerol, G1 tri-glycerol dendrons and
related esters for the first time using 4-nitrophenyl 2-(tert-butoxycarbonyl)acetate (Boc-gly-Ph-pNO2)
(2) as the acylating agent. This methodology offers efficient and controlled loading of amino acid
(glycine) on polyhydroxy compounds.
delivery, as well as release of bioactive molecules in regenerative
Introduction
medicine in the form of non-fouling surfaces and matrix materials.
One of the major problems emphasized in the construction of com-
The presence of amine groups on the surface or focal point in
plex polyfunctional molecules, i.e. mono- and oligosaccharides,
polyglycerol (PG) architectures has been useful as an anchoring
point in the preparation of protein resistant surfaces,15,16 in the
synthesis of macromolecular prodrugs,17,18 and in the condensation
of nucleic acid drugs.19–23 The amount and localization of amine
groups within the PG scaffold has shown to have an effect on sev-
eral properties related to drug coupling efficiency, cellular uptake,
gene transfection efficiency, toxicity, and unspecific interactions
(e.g. to albumin).24 To better tune these properties on polyglycerol
amine compounds, it is relevant to develop a synthetic method-
ology which allows control of the loading and localization of the
amine moieties. It is therefore interesting to explore the possibility
of biocatalyzed regioselective esterification/transesterification of
polyhydroxy compounds such as glycerol, dendritic generation
analogues of glycerol and related compounds, which find potential
applications in protein resistant surface coating materials, and
drug, dye, and gene delivery.
Amino acids are naturally occuring building blocks and can be
used as biodegradable linkers. We have chosen N-Boc-glycine 4-
nitrophenyl ester (2) for the selective acylation of hydroxyl groups
for biocatalytic transesterification reactions as this acylating agent
allows the selective loading of glycine (the simplest amino acid),
which ultimately allows the controlled loading of single primary
amine functionality in the compound, after deprotection of the
Boc-group. To the best of our knowledge, we are the first to use this
protected amino acid for selectively protecting hydroxyl groups in
biocatalytic transesterification reactions.
nucleosides, and dendrimers is the presence of multiple function-
alities of nearly identical reactivities which are difficult to protect
and deprotect selectively.1,2 Many classical chemical methods have
been developed for the manipulation of hydroxyl groups using
different protecting groups under mild conditions.3,4 Furthermore,
synthetic routes involving various protection and/or deprotection
steps reduce the overall yields of the desired products and make
the whole process tedious, time-consuming, and inefficient.2,5
Attempts to exploit the same or similar tools as nature to
perform comparable reactions have led to an extended use of
biocatalysts, which have substantially enriched the arsenal of
available protecting group techniques, offering viable alternatives
to classical methods.6,7
Recent advances in enzyme-assisted organic synthesis have
allowed the preparation of structurally well-defined molecules
in high yields and greater selectivity. Among the differ-
ent biocatalytic processes, lipase-catalyzed selective esterifica-
tion/transesterification reactions represent an important class of
enzymatic transformations in organic synthesis, which is mainly
attributed to the low cost of lipases and their wide tolerance
towards a variety of reaction conditions and substrates.8,9 Due to
their high versatility recognizing a broad range of substrates with
high regio- and enantioselectivity, lipases could be an attractive
alternative to obtain high specificity and regioselectivity.10–13
Dendritic polymeric architectures derived from polyglycerol
(PG) have been extensively used in the design of scaffolds in several
biomedical applications.14 Due to their highly biocompatible na-
ture, dendritic PGs show a broad range of potential applications in
medicine and pharmacology, e.g. transport and stimuli-responsive
In the present study, we also show a highly efficient temperature
dependent chemo-enzymatic route for the regioselective acylation
of potentially useful polyhydroxy compounds as well as subse-
quent reactions leading to the synthesis of amino acid-based
amphiphiles.
aBioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi
110 007, India. E-mail: virparmar@gmail.com; Fax: +91-11-27667206;
Tel: +91-11-27666555
Results and discussion
bInstitut fu¨r Chemie und Biochemie, Freie Universita¨t Berlin, Takustr. 3,
14195, Berlin, Germany. E-mail: haag@chemie.fu-berlin.de; Fax: (+49)
30-838-53357
Multiple approaches to design different PG architectures have
been reported that offer a great variety in the degree of branching,
size, surface topology, and chemical properties in general.14 The
use of PG dendrons as building blocks may allow a great
† Electronic supplementary information (ESI) available: 1H NMR and 13
C
NMR spectra of compounds 3, 4, 11, 13, 16, 17, 18, 19, 25 and 29. See
DOI: 10.1039/b927021c
2228 | Org. Biomol. Chem., 2010, 8, 2228–2237
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
diversity of polymeric architectures with potential for biomedical
applications.14
simultaneously esterified in one step to afford the compound 4 in
65% yield (Scheme 1).
We were interested in the selective/quantitative surface modifi-
cations of the [G1.0] glycerol dendrons in an endeavor to explore
the effect of quantitative glycine amino acid loadings along with
the hydroxyl groups of the dendrons. Consequently a number
of terminal amine functionalities could also be controlled on
the surface of the dendrimer. These assumptions prompted us
to synthesize [G1.0] dendrons with selective glycine loadings via
chemo-enzymatic pathways.
Based on our earlier experience of biocatalytic transacylation
reactions on polyhydroxy compounds,25–29 we chose to use the
enzymes Candida antarctica lipase-B immobilized on polyacrylate
(Lewatit), commonly known as Novozyme-435, porcine pancre-
atic lipase (PPL), Candida rugosa lipase (CRL), Theremomyces
To ascertain whether the primary or secondary hydroxyl group
of glycerol was esterified, we have compared the DEPT-NMR
spectrum of compounds 1, 3 and 4 (Fig. 1). In glycerol (1), peaks
corresponding to methylene carbons C-1 and C-3 appeared at
the same chemical shift value of d 63.08 as a downward signal
due to symmetry in the molecule, whereas the C-2 appeared
at d 72.58 as an upward signal. When the compound 1 was
regioselectively esterified and converted to compound 3 using
N-Boc-glycine 4-nitrophenyl ester (2), two peaks appeared as
downward absorptions in the DEPT NMR spectrum of compound
3 at d 62.63 and d 65.82, corresponding to C-3¢ and C-1¢,
respectively (Fig. 1). The peak for the C-2¢ appeared at d 69.70
while C-2 appeared at d 41.75. These observations from the
DEPT spectrum of compound 3 indicated that only one of the
primary hydroxyl group of glycerol (1) was esterified. We would
have expected only one peak as a downward absorption in the
DEPT spectrum if the secondary hydroxyl group of glycerol (1)
had been esterified. When compound 3 was further converted to
compound 4, the DEPT spectrum of the compound 4 revealed
one peak at d 65.30 as a downward absorption, corresponding to
equivalent carbons, i.e. C-1 and C-3 carrying the ester moieties
(due to symmetry in the molecule). The peak for C-2 appeared at
R
lanuginosus lipase immobilized on silica (Lipozymeꢀ TL IM)
and the Candida antarctica lipase-B immobilized on accurel
[CAL B-L(A)] for selective transestrification reactions on glycerol,
dendritic generation analogues of glycerol and related polyhydroxy
compounds in different solvents at two different temperatures.
We first carried out regioselective transesterification reactions
on glycerol (1) in the presence of the above-mentioned lipases
using N-Boc-glycine 4-nitrophenyl ester (2) as the acylating
reagent for the selective protection of hydroxyl groups at two
different temperatures (50 and 70 ◦C) in different organic solvents.
R
Lipozymeꢀ TL IM in dioxane was found to be the most efficient
biocatalyst for the regioselective transesterification on glycerol (1)
to afford mono- and di-esterified products (Scheme 1). The other
four lipases, i.e. Novozyme-435, PPL, CRL, and CAL B–L(A),
did not accept the substrate. When transesterification was carried
out at 50 ◦C for 30 h, only one primary hydroxyl group of glycerol
was esterified to afford the compound 3 in 78% isolated yield
(Scheme 1). When the compound 3 was further subjected to a
transesterification reaction with N-Boc-glycine 4-nitrophenyl ester
(2) for another 30 h at 50 ◦C in dioxane solvent, the second primary
hydroxyl group was also esterified to afford the compound 4 in
75% yield. When the same transesterification reaction was carried
out at 70 ◦C for 72 h, both the primary hydroxyl groups were
Fig. 1 Comparison of the DEPT-135 spectra of 1, 3 and 4.
Scheme 1 Lipozyme-catalyzed transesterification of glycerol.
The Royal Society of Chemistry 2010 Org. Biomol. Chem., 2010, 8, 2228–2237 | 2229
This journal is
©

View Article Online
d 66.89 as an upward signal and the C-2¢ showed up at d 41.70 as
a downward absorption (Fig. 1). The peak corresponding to C-3¢
at d 62.63 in compound 3 disappeared in the DEPT-135 spectrum
of compound 4 (Fig. 1). These observations led to the conclusion
that esterification took place at both primary hydroxyl groups and
not on secondary hydroxyl group.
To ascertain whether compound 3 is optically active we have
recorded its optical rotation, but this compound did not show any
optical rotation. Hence, no enantioselectivity was observed in case
of compound 3.
mono-esterified compounds 11 and 12, when further subjected
to lipozyme-catalyzed transesterification reaction with N-Boc-
glycine 4-nitrophenyl ester (2) for another 30 h at 50 ◦C in dioxane,
afforded compounds 13 and 14 (with both the primary hydroxyl
groups esterified) in 71 and 73% yields, respectively. The same
transesterification reaction, when carried out on compounds 8
and 10 at 70 ◦C for 72 h, afforded the di-esterified products 13
and 14 in 68 and 69% yields, respectively, with both the primary
hydroxyl groups esterified (Scheme 3).
To confirm whether primary or secondary hydroxyl groups were
esterified during the biocatalytic transesterification reactions on
compounds 8 and 10 shown in Scheme 3, we performed DEPT
NMR studies on compounds 10, 12, and 14 (Fig. 2). The DEPT
spectrum of compound 10 revealed the appearance of a peak at
d 63.14 for the two C-3¢ carbons as a downward signal, while
the two C-2¢ carbons appeared at d 70.89 as an upward signal,
due to symmetry in the molecule (Fig. 2). When compound 10
was converted biocatalytically to compound 12, the DEPT NMR
spectrum of compound 12 showed the appearance of peaks at
d 63.09 and d 65.86 for the C-3¢¢¢ and C-1¢, respectively, as
downward signals (Fig. 2). The appearance of a peak at d 65.86
as a downward absorption indicated that the primary hydroxyl
group was esterified. When compound 12 was further converted
to compound 14, the DEPT-135 NMR spectrum of compound
14 revealed the disappearance of the peak at d 63.09 (present in
compound 12 for C-3¢¢¢) and appearance of only one peak for
equivalent carbons, i.e. C-3¢ at d 65.89 as a downward absorption
due to symmetry in the molecule (Fig. 2). This confirmed that the
primary hydroxyl group was again esterified when compound 12
was converted to compound 14. In dendrons 8 and 10–14 different
diastereoisomers did not give rise to more distinctly dispersed
bunches of peaks in 13C NMR for corresponding carbons rather
than the single, albeit broadened lines, due to the polar and protic
nature of the solvent (CD3OD) in which we recorded our NMR
spectra. Also, these compounds were insoluble in comparatively
nonpolar solvents like CDCl3, in which one might be able to see
diastereoisomeric carbons. We had recorded the spectra in DMSO-
d6 as well but the spectra were not clear. Dendrons 12 and 14 could
be modified by azido alkanethiols via click reaction to form SAMs
on gold chips, and after Boc-deprotection their protein-resistant
behavior could then be analyzed.
Prompted by the regioselectivity achieved in case of glycerol,
we then extended this methodology on bifunctional G1 glycerol
dendrons, viz. on compounds 8 and 10 bearing four hydroxyl
groups (two primary and two secondary hydroxyl groups), which
were prepared according to the synthetic pathway shown in
Scheme 2. Compounds 6, 7, and 8 were previously reported by
us.30
Impressed by the regioselectivity achieved in G1 glycerol den-
drons 8 and 10, we extended the application of this methodology to
the synthesis of novel amino acid-based amphiphiles in an attempt
to prepare hydrophobic dendrons as potential gene carriers. For
this, we first prepared the octadecyl-propargyl ether with the
help of a literature procedure31 and then performed the click
reaction on compound 8 with octadecyl-propargyl ether using
copper triphenylphosphine bromide, diisopropylamine, and N,N-
dimethylformamide as a solvent at 50 ◦C for 24 h to afford
compound 15 in 83% yield (Scheme 4). Compound 15 was then
transesterified using N-Boc-glycine 4-nitrophenyl ester (2) as the
acylating agent in the presence of lipozyme at 50 and 70 ◦C
in dioxane solvent to furnish compounds 16 and 17 in 77 and
69% isolated yields, respectively (Scheme 4). Compound 16, when
transesterified at 50 ◦C for 30 h using N-Boc-glycine 4-nitrophenyl
ester (2) as the acylating agent in the presence of lipozyme in
dioxane solvent, afforded compound 17 in 74% isolated yield
(Scheme 4). Compounds 16 and 17 were then treated overnight
Scheme 2 Synthesis of bifunctional G1 glycerol dendrons 8 and 10.
Lipozyme-catalyzed biocatalytic transesterification reactions
on compounds 8 and 10 using N-Boc-glycine 4-nitrophenyl ester
(2) at 50 ◦C for 30 h in dioxane afforded compounds 11 and 12 in
81 and 76% isolated yields, respectively, in which only one primary
hydroxyl group in both the cases was esterified (Scheme 3). The
2230 | Org. Biomol. Chem., 2010, 8, 2228–2237
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Scheme 3 Lipozyme-catalyzed transesterification of G1 generation dendrons 8 and 10.
Fig. 2 Comparison of the DEPT-135 spectra of 10, 12 and 14.
with a mixture of trifluoroacetic acid : dichloromethane (1 : 3) to
afford monoamino and diamino dendrons 18 and 19, respectively
in 90% yields (Scheme 5). DNA complexation and binding studies
on dendrons 18 and 19 are currently under way.
the mono-esterified compounds 25 and 26 in 71 and 74% yields,
respectively (Scheme 6). The 2-methylpropanoate derivatives 23
and 24 were prepared in one step according to the literature
reported procedure.32
To ascertain the broader applicability of our above developed
chemo-enzymatic methodology, we envisaged extending it to other
polyhydroxy compounds, viz. 23 and 24 as well, which are the start-
ing materials for the synthesis of functionalized dendritic aliphatic
polyesters based on 2,2-bis(hydroxymethyl)propanoic acid (20).32
We have carried out lipozyme-catalyzed transesterification using
N-Boc-glycine 4-nitrophenyl ester (2) as the acylating reagent
on compounds 23 and 24 (both having two primary hydroxyl
groups) in dioxane at 50 ◦C for 72 h to afford regioselectively
Encouraged by the results on highly regioselective biocat-
alytic acylations on different compounds containing two pri-
mary hydroxyl groups, we attempted to apply this method-
ology to molecules containing three primary hydroxyl groups
as well. Regioselective protection of commercially available
2-(hydroxymethyl)-2-nitropropane-1,3-diol (27) and 2-ethyl-2-
(hydroxymethyl)propane-1,3-diol (28), both containing three pri-
mary hydroxyl groups, was also achieved by the lipozyme-
catalyzed transesterification using N-Boc-glycine 4-nitrophenyl
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2228–2237 | 2231
©

View Article Online
Scheme 4 Lipozyme catalyzed transesterification of G1 generation click dendron 15.
Scheme 5 Boc-deprotection of 16 and 17.
ester (2) as the acylating reagent. At 50 ◦C, only one primary
hydroxyl group was esterified in 72 h in both the compounds 27
and 28 to afford the compounds 29 and 30 in 80 and 78% yields, re-
spectively (Scheme 7). Only one out of the three primary hydroxyl
groups was regioselectively acylated using this methodology.
When mono-esterified compounds 29 and 30 were further
subjected to biocatalytic transesterification with N-Boc-glycine
4-nitrophenyl ester (2) at 50 C in dioxane solvent, the reaction
mixture became very complex to be handled for work-up and
purification of the reaction mass. Also, while performing the
◦
2232 | Org. Biomol. Chem., 2010, 8, 2228–2237
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Scheme 6 Lipozyme-catalyzed transesterification of 23 and 24.
Scheme 7 Lipozyme-catalyzed transesterification of 27 and 28.
same transesterification reaction on compounds 27 and 28 at
General procedure for the selective esterification of hydroxyl
groups using Boc-Gly-Ph-pNO2 (2)
70 ◦C, the reaction mixture became too complex to be handled
further.
The appropriate polyol compound (1, 8, 10, 15, 23, 24, 27, and
28) and Boc-Gly-Ph-pNO2 (4.0 mol equiv., 2) were dissolved
in dry dioxane (15 ml); lipozyme (50% by weight of the polyol
compound) and activated molecular sieves were added to it. The
reaction mixture was left for stirring at 50 ◦C for 30–72 h and
monitored by TLC; after completion of reaction, lipozyme and
molecular sieves were filtered off. The solvent was then removed
under reduced pressure and the residue subjected to column
chromatography. Elution with a mixture of 10% methanol : 90%
chloroform gave the desired mono-esterified products (3, 11,
12, 16, 25, 26, 29, and 30, respectively) in 70–80% isolated
yields.
The di-esterified compounds 4, 13, 14, and 17 were obtained
in 71–75% yields when the same transesterification reaction was
performed with lipozyme and the acylating agent 2 in dioxane
at 50 ◦C for 30 h on compounds 3, 11, 12, and 16, respectively
(Route-A).
The fourteen novel esters 3, 4, 11–14, 16–19, 25, 26, 29, and 30
have been prepared for the first time via chemo-enzymatic routes
and were unambiguously characterized using 1H NMR, 13C NMR,
DEPT, FT-IR, and HRMS techniques.
Experimental
Reactions requiring dry conditions were carried out under argon.
Dry and analytical-grade solvents and reagents were purchased
from Sigma-Aldrich and Acros and used as received. N-Boc-
glycine 4-nitrophenyl ester (2) was purchased from Fluka and
lipozyme was a gift from Novozymes A/s, Copenhagen, Denmark.
The 1H and 13C NMR spectra were recorded on a Bruker
DRX 400 spectrometer operating at 400 MHz and 100.5 MHz,
respectively. Column chromatography was performed on silica gel
60 (230–400 mesh) with head pressure supplied by compressed air.
Infrared spectra (IR) were recorded as thin films between KBr
or CaF2 plates on a Bruker IFS 66 FT-IR spectrophotometer.
For ESI measurements, a TSQ 7000 (Finnigan Mat) instrument
and for high-resolution mass spectra, a JEOL JMS-SX-102A
spectrometer were used.
The same di-esterified compounds 4, 13, 14, and 17 were
obtained in 60–70% yields when the biocatalytic transesterification
reaction was performed with lipozyme and the glycine-derived
acylating agent 2 at 70 ◦C for 72 h on compounds 1, 8, 10, and 15,
respectively (Route-B).
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2228–2237 | 2233
©

View Article Online
2¢,3¢-Dihydroxypropyl 2-N-(t-butoxycarbonyl)aminoacetate (3)
d 2.84 (1H, m, C-3¢¢H), 3.46-3.48, 3.50-3.60 & 3.86-3.87 (15H,
3 m, C-1H, C-2H, C-3H, C-1¢H, C-2¢H and C-3¢H), 4.31 (2H, d,
J = 2.4 Hz, C-1¢¢H); 13C NMR (100.5 MHz, methanol-d4): d 57.01
(C-1¢¢), 63.14 (2x C-3¢), 70.75 (C-1 and C-3), 70.89 (2x C-2¢), 72.67
(2x C-1¢), 74.56 (C-3¢¢), 76.52 (C-2), 79.65 (C-2¢¢); IR data (KBr)
Obtained as a light yellow viscous oil (1 g, 78% yield). Rf: 0.40
(1 : 5 methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
d 1.42 (9H, s, -OC(CH3)3), 3.53-3.54 (2H, m, C-3¢H), 3.66 (1H, m,
C-2¢H), 3.80 (2H, s, C-2H), 4.08-4.12 and 4.17-4.21 (2H, 2 m, C-
1¢aH and C-1¢bH); 13C NMR (100.5 MHz, methanol-d4): d 27.44
(-OC(CH3)3), 41.75 (C-2), 62.63 (C-3¢), 65.82 (C-1¢), 69.70 (C-2¢),
79.42 (-OC(CH3)3), 157.22 (NHCO), 170.81 (-CH2OCO); IR data
(film) nmax: 3396 (NH and OH), 1746 (-COO-), 1694 (CONH),
1422, 1265 and 741 cm-1; HRMS: m/z Calcd for C10H19NO6Na
[M+Na]+: 272.1110. Found: 272.1114.
n
max: 3377 (OH), 1593, 1457, 1384, 1047 and 662 cm-1; HRMS:
m/z Calcd for C12H22O7Na [M+Na]+: 301.1263. Found: 301.1270
Compound 11
Obtained as a light yellow viscous oil (386 mg, 81% yield). Rf:
0.35 (1 : 5 methanol–chloroform). 1H NMR (400 MHz, methanol-
d4): d 1.42 (9H, s, -OC(CH3)3), 3.48-3.60, 3.69-3.73, 3.92-3.94
& 4.10-4.22 (15H, 4 m, C-1¢H, C-2¢H, C-3¢H, C-1¢¢H, C-2¢¢H,
C-3¢¢H, C-1¢¢¢H, C-2¢¢¢H and C-3¢¢¢H), 3.80 (2H, s, C-2H); 13C
NMR (100.5 MHz, methanol-d4): d 27.42 (-OC(CH3)3), 41.75
(C-2), 60.65 (C-2¢¢), 62.94 (C-3¢¢¢), 65.80 (C-1¢), 68.03 (C-2¢),
70.75 (C-1¢¢ and C-3¢¢), 70.78 (C-2¢¢¢), 71.99 (C-1¢¢¢), 72.34 (C-3¢),
79.41 (-OC(CH3)3), 157.19 (NHCO), 170.74 (C-1); IR data (KBr)
1,3-Bis-{2¢-N-(t-butoxycarbonyl)aminoacetoxy}propane-2-ol (4)
Obtained as a light yellow viscous oil (367 mg, 75% yield) from
route-A and (1.4 g, 65% yield) from route-B. Rf: 0.54 (1 : 5
methanol–chloroform). 1H NMR (400 MHz, methanol-d4): d 1.42
(18H, s, -OC(CH3)3), 3.80 (4H, s, C-2¢H), 4.01 (1H, p, J = 5.6 Hz,
C-2H), 4.14-4.17 (4H, m, C-1H and C-3H); 13C NMR (100.5 MHz,
methanol-d4): d 27.42 (2x -OC(CH3)3), 41.70 (2x C-2¢), 65.30 (C-1
and C-3), 66.89 (C-2), 79.39 (2x -OC(CH3)3), 157.21 (2x NHCO),
170.60 (2x C-1¢); IR data (film) nmax: 3449 (NH and OH), 1751
(-COO-), 1711 (CONH), 1421, 1265, 895 and 738 cm-1; HRMS:
m/z Calcd for C17H30N2O9Na [M+Na]+: 429.1849. Found:
429.1859.
n
max: 3396 (NH and OH), 2130 (N3 stretch), 1736 (-COO-), 1674
(CONH), 1520, 1367, 1162 and 1053 cm-1; HRMS: m/z Calcd for
C16H30N4O9Na [M+Na]+: 445.1910. Found: 445.1927.
Compound 12
Obtained as a light yellow viscous oil (356 mg, 76% yield). Rf:
1
0.31 (1 : 5 methanol–chloroform). H NMR (400 MHz, CDCl3):
Procedure for the synthesis of compounds 6, 7 and 8
d 1.44 (9H, s, -OC(CH3)3), 2.45 (1H, t, J = 2.4 Hz, C-3¢¢¢¢H),
2.87, 2.94 (3x–OH), 3.52-3.74, 3.85-3.87, 4.16-4.23 and 4.27-4.29
(17H, 4 m, C-1¢H, C-2¢H, C-3¢H, C-1¢¢H, C-2¢¢H, C-3¢¢H, C-1¢¢¢H,
C-2¢¢¢H, C-3¢¢¢H and C-1¢¢¢¢H), 3.92 (2H, d, J = 5.6 Hz, C-2H),
5.08 (1H, br s, NH); 13C NMR (100.5 MHz, methanol-d4): d 27.40
(-OC(CH3)3), 41.72 (C-2), 57.05 (C-1¢¢¢¢), 63.09 (C-3¢¢¢), 65.86 (C-
1¢), 68.06 (C-2¢), 70.83 (C-1¢¢ and C-3¢¢), 70.84 (C-2¢¢¢), 72.11 (C-
1¢¢¢), 72.59 (C-3¢), 74.53 (C-3¢¢¢¢), 76.65 (C-2¢¢), 79.12 (C-2¢¢¢¢), 79.39
Compounds 6, 7, and 8 were synthesized according to a published
procedure.30
Procedure for the synthesis of compound 9
Propargyl bromide (2.5 equiv.) was added to a solution of the
compound 6 (20 g, 0.062 mol) and sodium hydride (2.5 equiv.) in
dry tetrahydrofuran (70 ml) under argon. The reaction mixture
was then stirred at 40–50 ◦C for 24 h. After completion of
reaction, the reaction mixture was filtered and the solvent was
evaporated under vacuum. The crude product was further purified
by column chromatography on silica gel to give the product 9 as
a yellow viscous oil (21.2 g, 95% yield). Rf: 0.45 (1 : 5 methanol–
(-OC(CH3)3), 157.22 (NHCO), 170.76 (C-1); IR data (KBr) nmax
:
3388 (NH and OH), 1746 (-COO-), 1705 (CONH), 1514, 1368,
1265, 1164 and 737 cm-1; HRMS: m/z Calcd for C19H33NO10Na
[M+Na]+: 458.1997. Found: 458.1994.
Compound 13
1
chloroform). H NMR (400 MHz, CDCl3): d 1.25 & 1.31 (12H,
Obtained as a light yellow viscous oil (194 mg, 71% yield) from
route-A and (297 mg, 68% yield) from route-B. Rf: 0.49 (1 : 5,
methanol–chloroform); 1H NMR (400 MHz, methanol-d4): d
1.43 (18H, s, 2x -OC(CH3)3), 3.80 (4H, s, 2x C-2¢¢H), 3.51-3.52,
3.55-3.68, 3.92-3.94, 4.10-4.14 and 4.18-4.22 (15H, 5 m, C-1H,
C-2H, C-3H, 2x C-1¢H, 2x C-2¢H and 2x C-3¢H); 13C NMR
(100.5 MHz, methanol-d4): d 27.42 (2x -OC(CH3)3), 41.73 (2x
C-2¢¢), 60.57 (C-2), 65.80 (2x C-3¢), 68.02 (2x C-2¢), 70.76 (C-
1 and C-3), 72.01 (2x C-1¢), 79.37 (2x -OC(CH3)3, 157.20 (2x
NHCO), 170.72 (2x C-1¢¢); IR data (KBr) nmax: 3398 (NH and OH),
2106 (N3 stretch), 1750 (-COO-), 1697 (CONH), 1508, 1394, 1265,
1163, 1056 and 738 cm-1; HRMS: m/z Calcd for C23H41N5O12Na
[M+Na]+: 602.2644. Found: 602.2636.
2 s, 4 x -CH3), 2.36 (1H, m, C-3¢¢H), 3.37-3.55, 3.62-3.66, 3.92-4.04
& 4.13-4.17 (15H, 4 m, C-1H, C-2H, C-3H, C-1¢H, C-2¢H and C-
3¢H), 4.21-4.22 (2H, m, C-1¢¢H); 13C NMR (100.5 MHz, CDCl3):
d 25.42 & 26.77 (4 x–CH3), 57.69 (C-1¢¢), 66.72 & 66.88 (2x C-3¢),
71.42 (C-1 and C-3), 71.61 (2x C-2¢), 72.44 (2x C-1¢), 74.38 (C-3¢¢),
74.63 (C-2¢¢), 76.50 (C-2), 109.33 (2x C-5¢); IR data (KBr) nmax
:
3054 (HC alkyne stretch), 1594, 1372, 1265, 1081 and 738 cm-1;
HRMS: m/z Calcd for C18H30O7Na [M+Na]+: 381.1889. Found:
381.1902.
Procedure for the synthesis of compound 10
R
Ion-exchange resin Dowexꢀ 50 W was added to a solution of
the compound 9 (19.3 g, 55.88 mmol) in MeOH (100 ml), and
the mixture was heated at reflux overnight. The resin was filtered
off, and the residue was concentrated under vacuum to yield the
compound 10 as a yellow viscous oil (14.81 g, 99% yield). Rf: 0.20
(1 : 5 methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
Compound 14
Obtained as a light yellow viscous oil (300 mg, 73% yield) from
route-A and (367 mg, 69% yield) from route-B. Rf: 0.45 (1 : 5,
2234 | Org. Biomol. Chem., 2010, 8, 2228–2237
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
methanol–chloroform). 1H NMR (400 MHz, CDCl3): d 1.40
(18H, s, -OC(CH3)3), 2.45 (1H, s, C-3¢¢¢H), 2.62 (2x–OH), 3.42
(4H, s, 2x C-2¢¢H), 3.53-3.61, 3.89-3.99, 4.07-4.14 and 4.19-4.26
(17H, 4 m, C-1H, C-2H, C-3H, 2x C-1¢H, 2x C-2¢H, 2x C-3¢H
and C-1¢¢¢H), 5.28 (2H, br s, 2x CONH); 13C NMR (100.5 MHz,
methanol-d4): d 27.41 (2x -OC(CH3)3), 41.72 (2x C-2¢¢), 57.05
(C-1¢¢¢), 65.89 (2x C-3¢), 68.06 (2x C-2¢), 70.85 (C-1 and C-3),
72.13 (2x C-1¢), 74.54 (C-3¢¢¢), 76.65 (C-2), 79.35 (C-2¢¢¢), 79.75
(2x -OC(CH3)3, 157.18 (2x NHCO), 170.73 (2x C-1¢¢); IR data
(KBr) nmax: 3379 (NH and OH), 1738 (-COO-), 1711 (CONH),
1519, 1367, 1251, 1165, 1055 and 735 cm-1; HRMS: m/z Calcd for
C26H44N2O13Na [M+Na]+: 615.2741. Found: 615.2767.
methanol–chloroform). 1H NMR (400 MHz, methanol-d4): d
0.82 (3H, t, J = 6.8 Hz, C-18cH), 1.20 (28H, brs, C-3cH to
C-16cH), 1.36 (22H, brs, 2x -OC(CH3)3, C-2cH and C-17cH),
3.39-3.43, 3.52-3.54, 3.63-3.64, 3.84-3.88 and 3.97-4.01 (15H, m,
C-1H, C-2H, C-3H, C-1¢H, C-2¢H and C-3¢H), 3.69 (2H, brs, C-
1cH), 3.72 (4H, brs, C-2¢¢H), 4.49 (2H, s, C-1bH), 7.99 (1H, s,
C-5aH); 13C NMR (100.5 MHz, methanol-d4): d 13.17 (C-18c),
22.44, 25.92, 27.43, 29.18, 29.48 and 31.77 (C-2c to C-17c and 2x
-OC(CH3)3), 41.69 (2x C-2¢¢), 60.93 (C-2), 63.32 (C-1b), 65.58 (2x
C-3¢), 67.90 (2x C-2¢), 69.96 (C-1c), 70.46 (2x C-1¢), 71.86 (C-1 and
C-3), 79.32 (2x -OC(CH3)3), 123.76 (C-5a), 144.44 (C-4a), 157.19
(2xNHCO), 170.41 and 170.61 (2xC-1¢¢); IR data (KBr) nmax
:
3365 (NH and OH), 1751 (-COO-), 1701 (CONH), 1515, 1379,
1165, 1056 and 737 cm-1; HRMS: m/z Calcd for C44H81N5O13Na
[M+Na]+: 910.5729. Found: 910.5765.
Compound 15
Compound 8 (500 mg, 0.0018 mol), octadecyl-propargyl ether31
(1.5 mol eq.), N,N-diisopropyl ethylamine (1.5 mol eq.) and
copper triphenylphosphine bromide (catalytic amount) were dis-
solved in dimethylformamide and the reaction mixture was left
stirring at 50 ◦C for 24 h. The reaction mixture was monitored by
TLC and after completion of reaction, the solvent was removed
under reduced pressure and the residue subjected to column
chromatography. Elution with 20% methanol–chloroform gave the
desired product 15 (900 mg, 83% yield) as a light yellow viscous
General procedure for the synthesis of compounds 18 and 19
Compounds 16 and 17 (100 mg) were treated overnight with
a mixture of trifluoroacetic acid : dichloromethane (1 : 3). The
reaction mixture was evaporated under reduced pressure to afford
the mono and diamino aliphatic dendrons 18 and 19, respectively,
as viscous oils.
1
oil. Rf: 0.35 (1 : 5 methanol–chloroform); H NMR (400 MHz,
methanol-d4): d 0.87 (3H, t, J = 6.8 Hz, C-18¢¢¢¢H), 1.26 (30H,
brs, C-3cH to C-17cH), 1.56 (2H, brs, C-2cH), 3.43-3.53 (11H,
m, C-1¢H, C-2¢H, C-3¢H, C-2H), 3.71 (2H, brs, C-1cH), 3.92-3.98
(4H, m, C-1H and C-3H), 4.55 (2H, brs, C-1bH), 8.15 (1H, s,
C-5aH); 13C NMR (100.5 MHz, methanol-d4): d 13.16 (C-18c),
22.42, 25.91, 29.16, 29.32, 29.47, 31.76 (C-2c to C-17c), 61.11
(C-2), 62.84 (2x C-3¢), 63.40 (C-1b), 70.01 (2x C-1¢), 70.44 (C-1c),
70.63 (2x C-2¢), 72.32 & 72.45 (C-1 and C-3), 123.71 (C-5a), 144.43
Compound 18
Obtained as a dark yellow viscous oil (76 mg, 90% yield). Rf: 0.45
(1 : 5, methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
d 0.88 (3H, t, J = 6.8 Hz, C-18cH), 1.26 (30H, brs, C-3cH to
C-17cH), 1.54-156 (2H, m, C-2cH), 3.44-3.52 and 3.90-3.97 (17H,
2 m, C-1H, C-2H, C-3H, C-1¢H, C-2¢H, C-3¢H, C-1¢¢¢H, C-2¢¢¢H,
C-3¢¢¢H and C-1cH), 3.75 (2H, s, -NH2), 3.85 (2H, s, C-2¢¢H),
4.56 (2H, s, C-1bH), 7.95 (1H, s, C-5aH); 13C NMR (100.5 MHz,
methanol-d4): d 13.13 (C-18c), 22.40, 25.89, 29.14, 29.28, 29.45,
30.40, 31.74 and 35.70 (C-2c to C-17c), 39.74(C-2¢¢), 61.01 (C-2¢),
62.87 (C-3¢¢¢), 63.30 (C-1b), 66.59 (C-3¢), 67.66 (C-2¢), 69.93 &
69.99 (C-1¢ and C-1¢¢¢), 70.45 (C-1c), 70.70 (C-2¢¢¢), 71.63 & 72.38
(C-1 and C-3), 123.74 (C-5a), 144.51 (C-4a), 163.63(C-1¢¢); IR
data (KBr) nmax: 3398 (NH and OH), 1749 (-COO-), 1420, 1384,
1265, 895, 738 and 705 cm-1; HRMS: m/z Calcd for C32H63N4O8
[M+H]+: 631.4646. Found: 631.4659.
=
(C-4a); IR data (KBr) nmax: 3365 (OH), 1661 (-C C-), 1379, 1264,
1104, 1047 and 736 cm-1; HRMS: m/z Calcd for C30H59N3O7Na
[M+Na]+: 596.4251. Found: 596.4268.
Compound 16
Obtained as a yellow viscous oil (184 mg, 77% yield). Rf: 0.45 (1 : 5,
methanol–chloroform). 1H NMR (400 MHz, methanol-d4): d 0.88
(3H, t, J = 6.8 Hz, C-18cH), 1.28 (26H, brs, C-4cH to C-16cH),
1.42 (13H, brs, -OC(CH3)3, C-3cH and C-17cH), 1.54-1.57 (2H, m,
C-2cH), 3.43-3.50, 3.68-3.71 3.91-3.93 and 4.03-4.09 (17H, m, C-
1H, C-2H, C-3H, C-1¢H, C-2¢H, C-3¢H, C-1¢¢¢H, C-2¢¢¢H, C-3¢¢¢H
and C-1cH), 3.78 (2H, s, C-2¢¢H), 4.55 (2H, s, C-1bH), 8.06 (1H, s,
C-5aH); 13C NMR (100.5 MHz, methanol-d4): d 13.15 (C-18c),
22.42, 25.0, 29.16, 29.46, 30.38, 31.76 and 35.68 (C-2c to C-17c
and -OC(CH3)3), 41.71(C-2¢¢), 61.00 (C-2), 62.88 (C-3¢¢¢), 63.32
(C-1b), 65.57 (C-3¢), 67.87 (C-2¢), 69.92 & 70.02 (C-1¢¢¢ and C-1¢),
70.38 (C-1c), 70.77 (C-2¢¢¢), 72.36 & 72.45 (C-1 and C-3), 79.32
(-OC(CH3)3), 123.71 (C-5a), 144.43 (C-4a), 157.18 (NHCO),
163.55 (C-1¢¢); IR data (KBr) nmax: 3388 (NH and OH), 1749
(-COO-), 1662 (CONH), 1515, 1378, 1165, 1056 and 737 cm-1;
HRMS: m/z Calcd for C37H70N4O10Na [M+Na]+: 753.4990.
Found: 753.5011.
Compund 19
Obtained as a yellow viscous oil (70 mg, 90% yield). Rf: 0.50 (1 : 5,
methanol–chloroform). 1H NMR (400 MHz, methanol-d4): d 0.87
(3H, t, J = 6.8 Hz, C-18cH), 1.26 (30H, brs, C-3cH to C-17cH),
1.54-156 (2H, m, C-2cH), 3.45-3.52, 3.88-396 and 4.09-4.16 (17H,
3 m, C-1H, C-2H, C-3H, C-1¢H, C-2¢H, C-3¢H and C-1cH), 3.84
(4H, brs, C-2¢¢H), 4.56 (2H, s, C-1bH), 8.07 (1H, s, C-5aH); 13C
NMR (100.5 MHz, methanol-d4): d 13.14 (C-18c), 22.40, 25.89,
29.14, 29.45 and 31.74 (C-2c to C-17c), 39.71 (2x C-2¢¢), 60.95
(C-2), 63.30 (C-1b), 66.64 (2x C-3¢), 67.70 (2x C-2¢), 69.99 (C-1c),
70.48 (2x C-1¢), 71.66 (C-1 and C-3), 123.67 (C-5a), 144.45 (C-4a),
167.08 (2x C-1¢¢); IR data (KBr) nmax: 3395 (NH), 1747 (-COO-),
1384, 1203, 1128, 1050 and 722 cm-1; HRMS: m/z Calcd for
C34H66N5O9 [M+H]+: 688.4861. Found: 688.4900.
Compound 17
Obtained as a light yellow viscous oil (134 mg, 74% yield) from
route-A and (213 mg, 69% yield) from route-B. Rf: 0.50 (1 : 5,
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2228–2237 | 2235
©

View Article Online
General procedure for the synthesis of compounds 23 and 24
(C-1¢), 173.70 (C-1); IR data (KBr) nmax: 3449 (NH), 1750 (-COO-),
1714 (CONH), 1421, 1265, 1164, 895 and 738 cm-1; HRMS: m/z
Calcd for C19H26FNO7Na [M+Na]+: 422.1591. Found: 422.1586.
Compound 20 (400 mg, 0.0029 mol) was dissolved in DMF and
potassium carbonate (1.5 mol eq.) was added. Benzyl bromide
(21, 1.5 mol eq.) or 4-fluorobenzyl bromide (22, 1.5 mol eq.)
was added dropwise under an ice bath for 1 h and the reaction
mixture was left for stirring for 6 h. After completion of reaction,
the reaction mixture was poured over crushed ice and extracted
with ethyl acetate. The organic layer was then evaporated under
reduced pressure and the crude product obtained was purified by
column chromatography (60 : 40, ethyl acetate–hexane) to afford
compound 23 as white solid32 and compound 24 as viscous oil in
80 and 82% yields, respectively.
3¢-Hydroxy-2¢-hydroxymethyl-2¢-nitropropyl
2-N-(tert-butoxycarbonylamino)acetate (29)
Obtained as a dark yellow viscous oil (326 mg, 80% yield). Rf: 0.45
(1 : 5, methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
d 1.43 (9H, s, -OC(CH3)3), 3.79 (2H, s, C-2H), 3.93 (4H, s, C-
3¢H and C-1¢¢H), 4.58 (2H, s, C-1¢H); 13C NMR (100.5 MHz,
methanol-d4): d 27.37 (-OC(CH3)3), 41.65 (C-2), 59.56 & 59.99
(C-3¢ and C-1¢¢), 60.46 (C-1¢), 79.52 (-OC(CH3)3), 92.91 (C-
2¢), 157.24 (NHCO), 169.96 (C-1); IR data (KBr) nmax: 3382
(NH and OH), 1748 (-COO-), 1693 (CONH), 1548, 1162 and
1054 cm-1; HRMS: m/z Calcd for C11H20N2O8Na [M+Na]+:
331.1117. Found: 331.1126.
4-Fluorobenzyl 3-hydroxy-2-(hydroxymethyl)-2-methyl propanoate
(24)
Obtained as a colorless viscous oil (592 mg, 82% yield). Rf: 0.45
(1 : 5, methanol–chloroform). 1H NMR (300 MHz, CDCl3): d 1.06
(3H, s, -CH3), 2.97 (2 x OH), 3.82 (4H, dd, J = 11.4 Hz, J =
11.2 Hz, C-3H), 5.16 (2H, s, C-1¢H), 7.02 -7.08 (2H, m, C-3¢¢H
and C-5¢¢H), 7.31-7.36 (2H, m, C-2¢¢H and C-6¢¢H); 13C NMR
(75.5 MHZ, CDCl3): d 17.08 (-CH3), 49.25 (C-2) 65.97 (C-1¢),
68.14 (2 x C-3), 115.44 (C-3¢¢), 115.72 (C-5¢¢), 129.84 (C-2¢¢), 129.95
(C-6¢¢), 131.52 (d, J = 3 Hz, C-1¢¢), 162.66 (d, J = 246 Hz, C-4¢¢),
175.65 (C-1); IR (KBr): 3234 (OH), 1729 (-COO), 1513, 1224, 1047
and 831 cm-1; HRMS: m/z Calcd for C12H15FO4Na [M+Na]+:
265.0847. Found: 265.0848.
2¢,2¢-Bis(hydroxymethyl)butyl
2-N-(tert-butoxycarbonylamino)acetate (30)
Obtained as a light yellow viscous oil (338 mg, 78% yield). Rf: 0.55
(1 : 5, methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
d 0.86 (3H, t, J = 7.6 Hz, C-4¢H), 1.37 (2H, q, J = 7.2 Hz, C-
3¢H), 1.43 (9H, s, -OC(CH3)3), 3.45 (4H, s, C-1¢¢H and C-1¢¢¢H),
3.77 (2H, s, C-2H), 4.02 (2H, s, C-1¢H). 13C NMR (100.5 MHz,
methanol-d4): d 6.36 (C-4¢), 21.53 (C-3¢), 27.41 (-OC(CH3)3), 41.83
(C-2), 42.79 (C-2¢), 61.70 (C-1¢¢ and C-1¢¢¢), 64.69 (C-1¢), 79.35
(-OC(CH3)3), 157.22 (NHCO), 170.92 (C-1); IR data (KBr) nmax
:
Benzyl 2-{(2¢-N-(tert-butoxycarbonylamino)acetoxymethyl}-3-
3447 (NH), 1742 (-COO-), 1713 (CONH), 1674, 1421, 1265, 895
and 738 cm-1; HRMS: m/z Calcd for C13H25NO6Na [M+Na]+:
314.1580. Found: 314.1584.
hydroxy-2-methylpropanoate (25)
Obtained as a light yellow viscous oil (240 mg, 71% yield). Rf:
0.60 (1 : 5 methanol–chloroform). 1H NMR (400 MHz, methanol-
d4): d 1.18 (3H, s, -CH3), 1.42 (9H, s, -OC(CH3)3), 3.65-3.70
(2H, m, C-3H), 3.77 (2H, s, C-2¢H), 4.32 (2H, s, C-1¢¢H), 5.13
(2H, s, C-1¢¢¢H), 7.29-7.35 (5H, m, C-2¢¢¢¢H, C-3¢¢¢¢H, C-4¢¢¢¢H, C-
5¢¢¢¢H and C-6¢¢¢¢H); 13C NMR (100.5 MHz, methanol-d4): d 16.37
(-CH3), 27.39 (-OC(CH3)3), 41.65 (C-2¢), 62.46 (C-3), 64.04 (C-1¢¢),
66.25 (C-1¢¢¢), 78.16 (C-2), 79.34 (-OC(CH3)3), 127.76 (C-2¢¢¢¢ and
C-6¢¢¢¢), 127.88 (C-4¢¢¢¢), 128.25 (C-3¢¢¢¢ and C-5¢¢¢¢), 136.185 (C-
1¢¢¢¢), 157.19 (NHCO), 170.64 (C-1¢), 173.79 (C-1); IR data (KBr)
Conclusions
In the present work, we have achieved the chemo-enzymatic regios-
elective synthesis of fourteen novel esters of glycerol, triglycerol
dendrons, and related esters, i.e. compounds 3, 4, 11–14, 16–19,
25, 26, 29, and 30 for the first time by biocatalytic transesteri-
fication using 4-nitrophenyl 2-(tert-butoxycarbonyl)acetate (Boc-
Gly-Ph-pNO2) (2) as the acylating agent. Temperature-dependent
lipozyme-catalyzed transesterification reactions of these polyhy-
droxy compounds were carried out in dioxane at 50 and 70 ◦C
to afford mono- and di-esterified products in good yields, re-
spectively. The protected amino acid, N-Boc-glycine 4-nitrophenyl
ester (2) has been used for the first time for selectively protecting
hydroxyl groups in biocatalytic transesterification reactions. This
methodology offers efficient and controlled loading of amino acid
(glycine) on polyhydroxy compounds and represents a platform
for the selective amino acid attachment (decoration) to the PG
scaffolds.
n
max: 3447 (NH and OH), 1751 (-COO-), 1712 (CONH), 1421,
1265, 1163, 895, 738 cm-1; HRMS: m/z Calcd for C19H27NO7Na
[M+Na]+: 404.1685. Found: 404.1708.
4-Fluorobenzyl 2-{(2¢-N-(tert-butoxycarbonylamino)
acetoxymethyl}-3-hydroxy-2-methylpropanoate (26)
Obtained as a light yellow viscous oil (244 mg, 74% yield). Rf: 0.55
(1 : 5, methanol–chloroform). 1H NMR (400 MHz, methanol-d4):
d 1.18 (3H, s, -CH3), 1.42 (9H, s, -OC(CH3)3), 3.66 and 3.79 (2H,
2d, J = 8.4 Hz, C-3Ha and C-3Hb), 3.72 (2H, s, C-2¢H), 4.25-4.32
(2H, m, C-1¢¢H), 5.11 (2H, s, C-1¢¢¢H), 7.04-7.08 (2H, m, C-3¢¢¢¢H
and C-5¢¢¢¢H), 7.35-7.39 (2H, m, C-2¢¢¢¢H and C-6¢¢¢¢H); 13C NMR
(100.5 MHz, methanol-d4): d 16.45 (-CH3), 27.50 (-OC(CH3)3),
41.72 (C-2¢), 64.08 (C-3), 65.05 (C-1¢¢), 65.98 (C-1¢¢¢), 78.16 (C-2),
79.39 (-OC(CH3)3), 115.01 (d, J = 21.7 Hz, C-3¢¢¢¢ and C-5¢¢¢¢),
129.99 (d, J = 8.4 Hz, C-2¢¢¢¢ and C-6¢¢¢¢), 132.23 (d, J = 3.3 Hz,
C-1¢¢¢¢), 157.08 (NHCO), 162.67 (d, J = 245.2 Hz, C-4¢¢¢¢), 170.52
Acknowledgements
We thank the Department of Biotechnology (DBT, New Delhi,
India) and the International Bureau (IB) of the Federal Ministry
of Education and Research (BMBF, Bonn, Germany) for the
financial assistance to this work.
2236 | Org. Biomol. Chem., 2010, 8, 2228–2237
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
17 F. Kratz, R. Haag and M. Calderon, PCT-Ameldung, 2009,
EP2009/002346.
Notes and references
1 P. Collins and R. Ferrier, Monosaccharides: Their Chemistry and Their
Roles in Natural Products, Wiley, UK, 1995, p. 431.
2 A. K. Prasad and J. Wengel, Nucleosides, Nucleotides Nucleic Acids,
1996, 15, 1347.
3 T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis,
Wiley and Sons, New York, 1991.
4 H. Kunz and H. Waldmann, Comprehensive Organic Synthesis, ed.
B. M. Trost, I. Flemming and E. Winterfeldt, Pergamon Press, Oxford,
1991, vol. 6, 631.
5 E. J. Reist, L. V. Fisher and L. Goodman, J. Org. Chem., 1968, 33,
189.
6 M. C. De Zoete, F. V. Rantwijk and R. A. Sheldon, Catal. Today, 1994,
22, 563.
7 H. Waldmann, J. Prakt. Chem., 1993, 335, 109.
8 K. Faber, Biotransformations in Organic Chemistry, Springer-Verlag,
Berlin Heidelberg, 5th edn, 2004.
9 K. Drauz and H. Waldmann, Enzyme Catalysis in Organic Synthesis,
VCH, Weinheim, vol. 1 and 2, 1994.
18 M. Calderon, R. Graeser, F. Kratz and R. Haag, Bioorg. Med. Chem.
Lett., 2009, 19, 3725.
19 L. A. Tziveleka, A. M. Psarra, D. Tsiourvas and C. M. Paleos,
Int. J. Pharm., 2008, 356, 314.
20 R. K. Kainthan, M. Gnanamani, M. Ganguli, T. Ghosh, D. E. Brooks,
S. Maiti and J. N. Kizhakkedathu, Biomaterials, 2006, 27, 5377.
21 O. Germershaus, M. Neu, M. Behe and T. Kissel, Bioconjugate Chem.,
2008, 19, 244.
22 P. Ofek, W. Fischer, M. Caldero´n, R. Haag and R. Satchi-Fainaro,
submitted.
23 W. Fischer, M. Caldero´n, A. Schulz, I. Andreou, M. Weber and R.
Haag, submitted.
24 J. Khandare, A. Mohr, M. Calderon, P. Welker, K. Licha and R. Haag,
Biomaterials, DOI: 10.1016/j.biomaterials.2010.02.001.
25 V. S. Parmar, A. K. Prasad, P. K. Singh and S. Gupta, Tetrahedron:
Asymmetry, 1992, 3, 1395.
26 Himanshu, R. Tyagi, C. E. Olsen, W. Errington, V. S. Parmar and A. K.
Prasad, Bioorg. Med. Chem., 2002, 10, 963.
10 A. K. Prasad, N. Kalra, Y. Yadav, R. Kumar, S. K. Sharma, S. Patkar,
L. Lange, J. Wengel and V. S. Parmar, Chem. Commun., 2007, 2616.
11 A. K. Prasad, N. Kalra, Y. Yadav, S. K. Singh, S. K. Sharma, S. Patkar,
L. Lange, C. E. Olsen, J. Wengel and V. S. Parmar, Org. Biomol. Chem.,
2007, 5, 3524.
12 G. Wulff, J. Schmid and T. Verihoff, Carbohydrates as Organic Raw
Materials, ed. F. W. Lichtenthaler, VCH, Weinheim, 1991, pp. 311.
13 R. Lortie, Biotechnol. Adv., 1997, 15, 1.
27 A. K. Prasad, S. Roy, R. Kumar, N. Kalra, J. Wengel, C. E. Olsen, A. L.
Cholli, L. A. Samuelson, J. Kumar, A. C. Watterson, R. A. Gross and
V. S. P a r m a r , Tetrahedron, 2003, 59, 1333.
28 A. Bhattacharya, A. K. Prasad, J. Maity, Himanshu, Poonam, C. E.
Olsen, R. A. Gross and V. S. Parmar, Tetrahedron, 2003, 59, 10269.
29 Poonam, A. K. Prasad, C. Mukherjee, G. Shakya, G. K. Megawanshi,
J. Wengel, R. K. Saxena and V. S. Parmar, Pure Appl. Chem., 2005, 77,
237.
14 M. Calderon, M. Quadir, S. K. Sharma and R. Haag, Adv. Mater.,
2010, 22, 190.
15 M. Wyszogrodzka and R. Haag, Biomacromolecules, 2009, 10, 1043.
16 M. Wyszogrodzka and R. Haag, Langmuir, 2009, 25, 5703.
30 M. Wyszogrodzka and R. Haag, Chem.–Eur. J., 2008, 14, 9202.
31 G. Godeau, C. Staedel and P. Barthe, J. Med. Chem., 2008, 51, 4374.
32 H. Ihre, A. Hult, J. M. J. Frechet and I. Gitsov, Macromolecules, 1998,
31, 4061.
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2228–2237 | 2237
©