TOWARD IMAGING GLYCOTOOLS BY CLICK COUPLING - Click Chemistry in Glycoscience: New Developments and Strategies - page 180

Covalent bonding Complexation

Direct
labeling

Metal
chelating
group

Y

a c

Y Biomolecule

Y Y

d

PG

X

b

Prosthetic
group

Y

PG

Y

FIGURE 7.2 Strategies for the construction of radiotracers. (See color plate section.)

prosthetic groups and to design new efficient coupling reactions of the latter to a given
biomolecule. On the one hand, the so-called “click chemistry” technologies [6] would
be of tremendous interest to provide valuable solutions to the coupling problem. On
the other hand, there is a long-standing interest in the use of sugars in the elaboration
of radiotracers and labeled complex carbohydrates themselves are interesting tools for
imaging [7]. Some reviews dealing with the use of click reactions in radiochemistry
[8-12] or in carbohydrate chemistry [13-15] have been published. The aim of this
chapter is to summarize different achievements recently reported which made use
of the two concepts for the elaboration of carbohydrate-using imaging tools. It is
important to note that the carbohydrate moiety can be used in different ways: as the
carrier of the radioelement ( 18 F), as a key element to improve the biokinetics of the
radiotracer or to participate in the chelation structure for radiometals ( 99m Tc, etc.).
In all cases, a robust and specific ligation method is sought for. This chapter will
be arranged according to the type of ligation or click reaction used (triazole, oxime
formation, etc.) and then to the type of compounds prepared (peptides, carbohydrates,
etc.)

7.3 TRIAZOLE-CONTAINING RADIOTRACERS

Since its revival in 2001, the Huisgen cycloaddition of an azide and an alkyne, now
catalyzed by Cu(I) [16, 17], has become the leading reaction in the “click chem-
istry” approach to achieve chemical ligation of two molecules [18]. Under the new
catalytic conditions, this triazole-forming reaction proceed readily, usually within