Improved performance by replacing iminodiacetic residues with glyceryl residues in symmetrically branched oligoglycerols

Article abstract of DOI:10.1016/j.bmcl.2011.06.064

Synthesis of a symmetrically branched diglycerol (BGL002, involving one iminodiacetic residue) as a G2 dendron, and the tetradecaglycerol (BGL014, involving one iminodiacetic residue) as a G4 dendron, is described. Several members of the BGL family of G2-

Full text of DOI:10.1016/j.bmcl.2011.06.064

Bioorganic & Medicinal Chemistry Letters 21 (2011) 4724–4727
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Bioorganic & Medicinal Chemistry Letters
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Improved performance by replacing iminodiacetic residues with glyceryl
residues in symmetrically branched oligoglycerols
Hisao Nemoto a, , Atsushi Ishihara b, Takaaki Araki a, Ayato Katagiri a, Masaki Kamiya a,
⇑
Tsuyoshi Matsushita a, Hatsuhiko Hattori a, Yukiteru Mimura b, Yutaka Tomoda b, Motoo Yamasaki c
a Department of Pharmaceutical Chemistry, Institute of Health Biosciences, Graduate School of The University of Tokushima, 1-78-1 Sho-machi, Tokushima 770-8505, Japan
b Drug Formulation Research and Development Laboratories, Production Division, Kyowa Hakko Kirin Co., Ltd, 1188 Shimotogari, Nagaizumi-cho, Sunto-gun,
Shizuoka 411-8731, Japan
c Innovative Drug Research Laboratories, Research Division, Kyowa Hakko Kirin Co., Ltd, 3-6-6 Asahi-machi, Machida, Tokyo 194-8533, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of a symmetrically branched diglycerol (BGL002, involving one iminodiacetic residue) as a G2
dendron, and the tetradecaglycerol (BGL014, involving one iminodiacetic residue) as a G4 dendron, is
described. Several members of the BGL family of G2–G4 dendrons were assembled, with G2 bearing four
hydroxyl groups at the terminus region, G3 bearing eight, and G4 bearing sixteen. It is noteworthy that
triglycerol (BGL003, including no iminodiacetic residue), has a water-solubility ten times higher than
BGL002, and the liposome surrounded by BGL014 has a duration period in blood vessel roughly two times
longer than the liposome surrounded by dodecaglycerol (BGL012, including three iminodiacetic
residues).
Received 15 April 2011
Revised 9 June 2011
Accepted 16 June 2011
Available online 25 June 2011
Keywords:
Symmetrically branched oligoglycerols
Dendron
Water-solubility
Liposome
Ó 2011 Elsevier Ltd. All rights reserved.
Duration period
Derivates of medicinal compounds with polyethylene glycol
(PEG) group attached via covalent bonding (PEGylation) have been
reported in the recent decades.1 Such PEGylation often provides
the derivatives with greater in vivo biologically or thermally stabil-
ity than the original molecules and/or a greater duration period in
blood vessels.
generation (G2) of dendron,8 a hexamer (BGL006)9,10 and a hepta-
mer (BGL007)11 as third generation (G3) of dendrons, and
dodecamer (BGL012)12 as a fourth generation (G4) of dendron,
To enhance such biologically favorable properties, glyceryl olig-
omers or polymers, mainly involving dendric skeletons, have also
been studied as rival candidates to PEG.2 As shown in Figure 1,
three basic types of oligomers 1, 2, and 3, can be listed. Although
a vague mixture probably containing 1 and 2 was reported in an
earlier papers,3 practical methods to produce oligomers with
known chemical structure came later with the synthesis of 1 by
Koma in 1986,4 and of 2 by Vanlerberghe in 1969,5 and also by
Yoshii et al.6 and Yasukochi et al.7 in 1997. In contrast, no reports
were made on symmetrically branched oligoglycerols 3 (BGL)
before our publication in 1992.8
The synthesis we developed for 3 yielded a single product (no
statistical mixture) with a peculiar symmetrical cascade-shape,
and no asymmetric center. Therefore 3 may be more potentially
applicable for medicinal use than 1 and 2. We have previously
reported the preparation of
a trimer (BGL003) as a second
⇑
Corresponding author.
E-mail address: nem@ph.tokushima-u.ac.jp (H. Nemoto).
Figure 1. Various oligoglycerols including our developed symmetrical ones.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.06.064

H. Nemoto et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4724–4727
4725
Figure 2. Previously prepared BGL family and newly disclosed two BGL (BGL002 and BGL014).
Scheme 1.
including the molecules with protecting groups (R) at the terminus
region and those with free hydrogens (R = H) (Fig. 2).
(benzotriazol-1-yloxy)tripyrrolidinophosphonium
hexafluoro-
phosphate (PyBOP) in DMF in the presence of diisopropylethyl-
amine (DIPEA) at room temperature for 9.5 h afforded 6 in 80%
yield. The Boc group of 6 was removed by trifluoroacetic acid
(TFA)/dichloromethane at room temperature for 30 h, then treat-
ment of succinic anhydride in pyridine at 100 °C for 15 h, and con-
densation of the resulting acid and N-hydroxysuccinimide (HOSu)
with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochlo-
ride (EDCÁHCl) in the presence of triethylamine (TEA) in THF at re-
flux for 18 h gave 7 in 68% yield from 6. Finally, condensation
between 7 and 815 in THF at room temperature for 40 h, followed
In this Letter, we describe the preparation of an alternative G2
dendron, BGL002 derivative 9 (Scheme 1) and a G4 dendron,
BGL014 derivative 17 (Scheme 2), to complement the existing
G2–G4 series of BGL family. Moreover, we report on the improved
performance obtained by replacing iminodiacetic residues with
glyceryl residues in the dendric BGL.
Because we have previously measured the water-solubility of
BGL003 derivative 10,9 an equivalent BGL002 derivative 9 was
prepared for comparison. Condensation of 413 and 514 using

4726
H. Nemoto et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4724–4727
Scheme 2.
by deprotection of the four benzyl groups in ethanol in the pres-
ence of palladium hydroxide on charcoal under a hydrogen atmo-
sphere for 7 h afforded 9 as a gummy solid in 71% from 7.
It is noteworthy that the water-solubility9 of 10 was signifi-
cantly higher than that of 9 (more than ten times), despite the fact
that both 9 and 10 have four hydroxyl groups. Consequently, the
number of primary hydroxyl groups at the terminus site was not
an exclusive factor in determining the water-solubility, which
was also strongly dependent on the apex region of the molecular
block comprising the dendron.
Based on the results described above, the water-solubility of
BGL014 is probably much higher than that of BGL012. However,
we did not obtain values for the water-solubility of the BGL012-8
and BGL014-8 conjugates because their water-solubility was too
great to measure. In fact, even the water-solubility of the
BGL006-8 conjugate was too high to be measured.9
gate 17 was synthesized from a BGL007 derivative 11,11 which has
an azido group at the apex region and bears four benzylidene pro-
tecting groups at the terminus region. To orthogonally deprotect
the benzylidene groups of 11, an iminodiacetic acid bearing the
2-nitrobenzenesulfonyl (Ns) group16 12 was prepared. After the
azido group of 11 was reduced with lithium aluminum hydride
in THF, condensation of the resulting amine with 12 afforded 13
in 86% yield by using PyBOP and DIPEA in DMF at 50 °C for 18 h.
After the deprotection of the Ns group16 of 13 by thioglycolic acid
and lithium hydroxide monohydrate in DMF at room temperature
for 2 h, condensation between the resulting amine and 2,5-dioxo-
pyrrolidin-1-yl 4-chloro-4-oxobutanoate (14)17 afforded 15 in
56% yield using 2,6-lutidine18 in DMF at 0 °C for 2 h. Finally, con-
densation of 15 and DSPE (16) in chloroform/methanol in the pres-
ence of TEA at room temperature for
7 days, followed by
deprotection of the eight benzylidene groups by palladium char-
coal in methanol/THF under hydrogen atmosphere at 50ꢀC for
6.5 h afforded 17 in 64% yield.
Next, we prepared a liposome including the 1,2-distearoylphos-
phatidylethanolamine (DSPE)–BGL014 conjugate 17 because we
have previously studied the properties of an equivalent liposome
including the DSPE–BGL012 conjugate 1812 (Scheme 2). The conju-
We disclose herein preliminary data on the duration in blood
vessels for the liposomes containing 17, 1812 and 1912 (L17, L18,

H. Nemoto et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4724–4727
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and L19, respectively) although a detailed comparison of various
properties for L17–L19 is currently underway.19 These three lipo-
somes were prepared according to our previous paper.12 The val-
ues as determined by analytical ultracentrifugation over 24 h
(AUC0–24) obtained for the control (neither PEG nor BGL), L17,
L18, and L19 liposomes were 1.8 0.9, 95.1 15.0, 53.1 27.6,
and 45.7 3.6 l
g mLÀ1 hÀ1, respectively. It is noteworthy that the
AUC0–24 value of L17 was larger than that of L18 (BGL014 versus
BGL012), and was also larger than that of L19 (BGL versus PEG).
Based on the observation that a BGL002 derivative 9 was more
easily solidified than a BGL003 derivative 10, the conformational
rigidity of the iminodiacetic residue was thought to be higher than
that of the glyceryl residue. It is considered that BGL003 can flex-
ibly interact with more water molecules via hydrogen bond inter-
actions than BGL002. Similarly, BGL014 can also interact with more
water molecules than BGL012.
In conclusion, we have successfully obtained various members
of the BGL family (G2–G4), and observed significant differences
resulting from the dendritic block unit between tetrahydroxyl
derivatives (BGL002 versus BGL003) and between hexadecahydr-
oxyl derivatives (BGL012 versus BGL014). Various studies utilizing
covalent bond formation with the BGL family (BGLation) including
liposome chemistry are in progress.
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4. Koma, T. Patent JP61238749, 1986.
5. Vanlerberghe, G. Patent DE1813226, 1969.
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Acknowledgments
10. Yamaguchi, H.; Suzawa, T.; Araki, T.; Kamiya, M.; Nemoto, H.; Yamasaki, M.
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11. Nemoto, H.; Kamiya, M.; Minami, Y.; Araki, T.; Kawamura, T. Synlett 2007,
2091.
12. Ishihara, A.; Yamauchi, M.; Kusano, H.; Mimura, M.; Nakakura, M.; Kamiya, M.;
Katagiri, A.; Kawano, M.; Nemoto, H.; Suzawa, T.; Yamasaki, M. Int. J. Pharm.
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13. Wang, Y. A.; Li, J. J.; Chen, H.; Peng, X. J. Am. Chem. Soc. 2002, 124,
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This work was partly supported by the Japan Science and Tech-
nology Agency (JST), Adaptable and Seamless Technology Transfer
Program through Target-driven R&D in 2009-2012.
Supplementary data
14. Nemoto, H.; Cai, J.; Yamamoto, Y. J. Med. Chem. 1995, 38, 1673.
15. Zaragoza-Dörwald, F.; Von Kiedrowski, G. Synthesis 1988, 917.
16. Fukuyama, T.; Cheung, M.; Kan, T. Synlett 1999, 1301.
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18. Our attempts for the preparation of 13 using various tertiary amines were
unsuccessful with the exception of 2,6-lutidine because the N-
hydroxysuccinimide ester moiety was decomposed by relatively unhindered
amines such as TEA, DIPEA, 4-(N,N-dimethylamino)pyridine, and 1,8-
diazabicyclo[5.4.0]undec-7-ene. In contrast, condensation reaction of the
resulting amine and acid chloride 14 was too slow with weak base such as
pyridine or N-methylmorpholine. The success with 2,6-lutidine was probably
due to its appropriate basicity and very hindered circumstance around the
amino group.
Supplementary data (procedures for synthesis of 9 and 17 are
available including 1H NMR, 13C NMR, IR, and high resolution mass
spectra data for 6, 7, 9, 13, and 15, and 1H NMR and low mass spec-
trum date for 17) associated with this article can be found, in the
online version, at doi:10.1016/j.bmcl.2011.06.064.
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