Efficient synthesis of a new potential chelating agent for radioimmunotherapy

Article abstract of DOI:10.1055/s-2002-35562

The synthesis of a new rigid analogue of cyclohexyl-TTHA, an efficient lanthanide ligand, as well, as the first complexation trials are reported. This polyaminopolycarboxylic acid, Ph-DTHA 1, was obtained in five steps from phenylenediamine as starting pr

Full text of DOI:10.1055/s-2002-35562

2080
LETTER
Efficient Synthesis of a New Potential Chelating Agent for Radioim-
munotherapy
New
P
otential
é
C
helating A
b
gent for Ra
a
dioimmuno
s
therapy tien G. Gouin,a,b Jean-François Gestin,b,c Patricia Remaud,b Alain Faivre-Chauvet,b Jean Claude Meslin,a
David Deniaud*a
a
Laboratoire de Synthèse Organique, UMR CNRS 6513, Faculté des Sciences et des Techniques, 2 rue de la Houssinière, BP 92208,
44072 Nantes Cedex, France
b
INSERM U463, Chimie des bioconjugués, 9 quai Moncousu, 44093 Nantes Cedex, France
Fax +33(251)125402; E-mail: david.deniaud@chimie.univ-nantes.fr
c
CHELATEC SAS, Institut de Biologie, 9 quai Moncousu, 44093 Nantes Cedex, France
Received 16 July 2002
influenced by the novel basicity and the interatomic dis-
tance of the two nitrogen atoms carried by the phenyl
group. The presence of the aromatic nucleus will also al-
low direct introduction of a nitro group as a precursor of
Abstract: The synthesis of a new rigid analogue of cyclohexyl-
TTHA, an efficient lanthanide ligand, as well, as the first complex-
ation trials are reported. This polyaminopolycarboxylic acid, Ph-
DTHA 1, was obtained in five steps from phenylenediamine as
starting product. The key intermediate was phenylenediethylenetet- an isothiocyanate function. In fact, this linkage is regular-
raamine 4, which after alkylation and hydrolysis gave the expected
compound 1 with ten coordination centers.
ly used to couple the radiolabeled molecule to the biolog-
ical vector.
Key words: ligands, polyaminopolycarboxylic acids, radioimmu-
notherapy, complexes, radionuclides
CO2H
CO2H
N
CO2H
N
CO2H
N
N
N
N
CO2H
CO2H
CO2H
CO2H
CO2H
N
CO2H
N
The development of radioimmunotherapy (RIT), a very
promising technique for the treatment of leukemia and
lymphoma,1 led us to devise new radionuclide chelating
agents.2 To achieve efficient complexation of the radio-
elements used in therapy (i.e. 90Y,153Sm,213Bi), these
agents should possess aminocarboxylic acid groups in
sufficient number to meet the coordination needs of the
CO2H
CO2H
cyclohexyl-TTHA
Ph-DTHA 1
Scheme 1
metals concerned. Moreover, several studies have shown The first step in the synthesis (Scheme 2) consisted of
that the rigidity of the carbon skeleton of the complexing acylating 1,2-phenylenediamine by carbobenzyloxygly-
molecule is an important consideration.3 In fact, a semi- cine, which was previously activated in the form of acid
rigid or rigid skeleton reduces the degrees of freedom of
chloride by addition of oxalyl chloride in the presence of
donor atoms (i.e. the notion of preorganization),4 thereby
a quatalytic amount of DMF.7 Contrary to classical cou-
significantly improving the stability of the complexes pling by 1,3-dicyclohexylcarbodiimide,8 this method en-
formed. A large number of new chelates have been creat- abled us to obtain the original product 2a quantitatively.
ed, by the various groups working on the development of Because of the high insolubility of compound 2a, it was
macrocyclic aminocarboxylic ligands, and rigid deriva- necessary to use the Pearlman catalyst9 [Pd(OH)2] in a
tives of diethylenetriamine pentaacetic acid (DTPA).5 2 M HCl–MeOH (1:1) mixture to deprotect the two amine
However, few studies have investigated the rigidification functions. Thus, product 3a was obtained in the form of
of triethylenetetraamine hexaacetic acid (TTHA), which dihydrochloride. At this stage, it was not possible to re-
led our group to file a patent concerning the synthesis of duce the carbonyl groups by borane, possibly because of
cyclohexyl-TTHA (Scheme 1), a ligand that has proved the total insolubility of the protonated form 3a in ordinary
efficient for RIT applications.6
organic solvents. As various attempts to isolate 3a in pure
free base form failed, it was necessary to revise the syn-
thesis strategy by modifying the glycine-protecting group.
The benzyloxycarbonyl group (Z) was then replaced by
the 9-fluorenylmethoxycarbonyl group (Fmoc). After
acylation by the corresponding acid chloride and then
deprotection of compound 2b by piperidine in DMF,10 the
free base 3b was isolated with an overall yield of 94%. A
classical reduction by the borane-methyl sulfide
complex11 in THF then gave, after an acid work-up, inter-
mediate 4 with a yield of 58%.12
This report describes the synthesis of a potential new
chelating agent, a rigid TTHA analogue designated as
phenylenediethylenetetraamine hexaacetic acid 1 (Ph-
DTHA). The substitution of an aromatic ring for cyclo-
hexane allowed the skeletal structure to be rigidified and
the degrees of freedom of donor atoms to be reduced even
more. It should be noted that complexation will also be
Synlett 2002, No. 12, Print: 02 12 2002.
Art Id.1437-2096,E;2002,0,12,2080,2082,ftx,en;G19902ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

LETTER
New Potential Chelating Agent for Radioimmunotherapy
2081
O
O
NR
NR
NH2
NH2
NH2
NH
NH
NH2
NH2
NH
NH
NH
NH
i
ii
iii
.X HCl
NH2
for 3b
O
O
2a R = Z (quant)
2b R = Fmoc (94%)
3a X = 2 (96%)
3b X = 0 (quant)
4
(58%)
Scheme 2 Reagents and conditions: (i) Z-gly or Fmoc-gly, Cl-(CO)2-Cl, DMF, 1 h, r.t., CH2Cl2 for 2a, THF for 2b. (ii) H2, Pd(OH)2,
2 M HCl–MeOH 1:1, 20 h, r.t. for 3a, piperidine, DMF, 0.5 h, r.t. for 3b. (iii) BH3–DMS, THF, 20 h, reflux.
R
CO2H
NH2
NH2
N
N
N
CO2H
NH
NH
N
N
N
N
ii
i
R
R
R
R
CO2H
CO2H
CO2H
N
R
CO2H
4
Ph-DTHA 1 (90%)
5
R = CO2t-Bu (41%)
Scheme 3 Reagents and conditions: (i) BrCH2CO2t-Bu, KI–K2CO3, CH3CN, 4 days, 80 °C, Ar. (ii) EtOH–NaOH 2 M, 12 h, 60 °C, then
HCl 6 M.
Tetraamine 4 was then alkylated (Scheme 3) by tert-butyl
bromoacetate in the presence of a catalytic amount of po-
tassium iodide and an excess of potassium carbonate,13
which led to hexaalkylated compound 5 with a yield of
41%. Acidic hydrolysis of tert-butylic esters according to
classical conditions was only partial,14 even after heating
in pure trifluoroacetic acid. Total deprotection was
achieved in EtOH–NaOH (2 M mixture) maintained at 60
°C for 12 h. After acidification of the reaction medium by
HCl (6 M) and evaporation under reduced pressure, prod-
uct 1 was extracted from the salts by acetone with a yield
of 90%.15
References
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Resche, I.; Mahe, M.; Charbonnel, B. Med. Nuc. I. Met.
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Preliminary complexation tests were performed between
compound 1 and a radioactive solution of yttrium (90Y).
Ligand 1 and the radionuclide were incubated for 1 h in a
sodium acetate buffer, pH 5.5, at 37 °C in very high dilu-
tion conditions ([90Y] = 0.1 nmol L–1). These tests showed
the formation of a complex between polyaminopolycar-
boxylated chelate 1 and 90Y.
(5) (a) Gouin, S. G.; Gestin, J.-F.; Reliquet, A.; Meslin, J.-C.;
Deniaud, D. Tetrahedron Lett. 2002, 43, 3003.
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Chem. 1995, 60, 6987.
In summary, a new chelating agent, an analogue of cyclo-
hexyl-TTHA, was synthesized in five steps with good
yields. Further studies will be conducted to quantify the
complexing properties of this molecule on yttrium and to
determine the serum stability of the complex formed. The
possibility of complexation with other radioelements suit-
able for RIT, such as samarium (153Sm) or bismuth (213Bi),
will also be investigated.
(6) Mease, R. C.; Srivastava, S. C.; Gestin, J.-F. Patent WO
5089663, 1992.
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Acknowledgement
The authors are grateful to the French Ministry of Education, the
CNRS, and the ‘Ligue Nationale Contre le Cancer’ for financial
support.
Synlett 2002, No. 12, 2080–2082 ISSN 0936-5214 © Thieme Stuttgart · New York

2082
S. G. Gouin et al.
LETTER
(11) (a) Moreau, P.; Tinkl, M.; Tsukazaki, M.; Bury, P. S.;
Griffen, E. J.; Snieckus, V.; Maharajh, R. B.; Kwork, C. S.;
Somayaji, V. V.; Peng, Z.; Sykes, T. R.; Noujaim, A. A.
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(15) Spectrum data of compound 1: IR (KBr): 3419, 2970, 1733,
1635, 1418, 1256 cm–1; 1H NMR (200 MHz, D2O): = 3.49
[4 H, m, 2 NCH2CH2N(CH2CO2H)2], 3.69 (4 H, m, 2
NCH2CH2N(CH2CO2H)2), 4.09 [4 H, s, 2 N(CH2CO2H)],
4.19 [8 H, s, 2 N(CH2CO2H)2], 7.13 (4 H, m, CHar);
13C NMR (50 MHz, D2O): = 50.4 [2
NCH2CH2N(CH2CO2H)2], 56.5 [2
NCH2CH2N(CH2CO2H)2], 57.3 [2 N(CH2CO2H)], 58.5 [2
N(CH2CO2H)2], 125.7 [2 CHar], 128.8 [2 CHar], 145.0
[2 Car], 171.9 [4 N(CH2CO2H)2], 178.2 [2
N(CH2CO2H)]; MS (ES+): = 543.1 (M + H+), 565.1 (M +
Na+); mp >300 °C.
Synlett 2002, No. 12, 2080–2082 ISSN 0936-5214 © Thieme Stuttgart · New York