Process for the preparation of tetraazamacrocycles

Details Process for the preparation of tetraazamacrocycles Process for the preparation of tetraazamacrocycles

1999-08-11

2000-11-21

Shah, Mukund J.

Organic compounds -- part of the class 532-570 series

Organic compounds

Unsubstituted hydrocarbyl chain between the ring and the -c-...

544343, 5483017, 5483021, C07D48722, C07D24100, C07D23500

Patent

active

06150520&

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the synthesis of compounds of general formula (I), useful intermediates for the synthesis of tetraazamacrocycles of general formula (II) ##STR3## in which n, p and q can independently be 0 or 1, ##STR4## wherein step a): condensation of the polyamine of-formula (III) with the glyoxal derivative of formula (IV), wherein Y is --OH (glyoxal hydrate) or [--SO.sub.3.sup.- Na.sup.+ ] (Bertagnini's salt), in water or in water-soluble solvents or in mixtures thereof, at a temperature of 0-50.degree. C., in the presence of stoichiometric amounts or of a slight excess of calcium hydroxide, to give the compound of formula (V); agent X--CH.sub.2 --(CH.sub.2).sub.q --CH.sub.2 --X, in which q is as previously defined and X is Cl or Br, in ratios of 1 to 5 mols per mol of compound (V), in a dipolar aprotic solvent and in the presence of a base selected from alkali or alkaline-earth metal carbonates, in ratios of 5 to 10 mols per mol of compound (V), and with the addition of NaZ, wherein Z is I or Br, as catalyst in ratios of 0.1 to 2 mols per mol of compound (V), wherein 150.degree. C., to give compound of formula (I).
The compounds of general formula (I) are important intermediates for the synthesis of tetraazamacrocycles of formula (II) according to the steps illustrated in Scheme 2, as already described in Italian Patent application MI 96A001257 and exemplified in the Experimental Section of the present Patent: ##STR5## wherein step c): oxidation of the compound of formula (II) with an oxidizing agent suitable for the aliphatic amines, in water or in a diphasic system consisting of water and an organic solvent, resistant to oxidative conditions, at a temperature of 0-100.degree. C., to give a mixture of oxidized products which is subjected directly to aqueous medium at pH higher than 12, at a temperature of 110-200.degree. C., to give the compound of formula (II).
The process of the present invention is particularly preferred for the preparation of decahydro-2a,4a,6a,8a-tetraazacyclopent[fg]acenaphthylene of formula (VI), an useful intermediate for the synthesis of 1,4,7,10-tetraazacyclododecane of formula (VII), ##STR6## which corresponds to the case in which in the compound of formula (I) n, p and q are 0.
1,4,7,10-Tetraazacyclododecane (commonly known as Cyclen) is the precursor for the synthesis of macrocyclic chelating agents for metal ions, as these chelating agents form very stable complexes with such ions.
In particular, the complexes with the paramagnetic metal ions, specifically the gadolinium ion, of said chelates can be used in the medical diagnostic field through Nuclear Magnetic Resonance technique, otherwise troublesome due to the high toxicity of the free ion.
At present, two contrast media are commercially available, namely Dotarem(.RTM.) and Prohance(.RTM.), two gadolinium complexes the chemical structure of which is based on Cyclen, while others are still under investigation. Therefore, it is important to work out a synthetic process for the preparation of said "building block", which is cost-saving and industrially advantageous.
It has surprisingly been found, and this is the object of the present invention, that the addition of NaZ in the step of formation of the compound of formula (I) starting from the intermediate of formula (V), remarkably improves yields, as evidenced in the Experimental section.
Particularly preferred is the use of 1,2-dichloroethane as (C-2)-alkylating agent, in addition to the use of NaBr as catalyst. This reactive combination turned out to be extremely advantageous both from an economical (increase in yields, low cost of the starting materials), and environmental point of view.
In particular, the improvement in yields, compared with the cases involving the use of only 1,2-dichloroethane or of only 1,2-dibromoethane, may be explained in terms of reactivity. 1,2-Dichloroethane is, in fact, not very reactive, whereas 1,2-dibromoethane is very reactive towards the intermediate (V): therefore, the reaction of 1,2-dichloroethane is

REFERENCES:
patent: 3932451 (1976-01-01), Bigelow et al.
Jazwinski et al, "Tricyclic . . . ," Tetrahedron Letters, vol. 22, No. 18, pp. 1711-1714 (1981).
Weisman et al, "Tetracyclic Tetraamines . . . ," Tetrahedron Letters, vol. 21, pp. 335-338 (1980).

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