Perfluoro-1-Azabicyclo(5,3,0)decane Compounds Useful as Blood Substitutes

This invention relates to novel perfluorinated heterocyclic compounds and emulsions containing them.

There is a need for a functional liquid to serve as a blood substitute and as a perfusate for organ preservation prior to transplant. Such a liquid should have adequate oxygen-carrying capacity and the ability to emulsify in aqueous media but should not be hydrolysed or otherwise degraded in body tissues.

Compounds used in a commercial blood substitute, Fluosol DA (R.T.M.), are perfluorodecalin (which does not easily give a stable emulsion in aqueous media) and perfluorotripropylamine (which gives a more stable emulsion than perfluorodecalin, but which has a longer retention time in the body).

This invention, in the first aspect, consists in novel perfluoroheterocyclic compounds perfluoroazabicyclodecane, C.sub.9 F.sub.17 N of boiling point 127.degree.-129.degree. C. and its lower (1-2 C-atom) homologues.

It is believed that these new compounds have a 7-membered ring fused with a 5-membered ring in their structure, as shown below: ##STR1##

The nitrogen atom in the new compounds is connected to 3-carbon atoms i.e. it is in a bridgehead position. The preferred homologue is a compound with a trifluoromethyl group in the .alpha.-position i.e. attached to a carbon atom adjacent to the N-atom.

In a second aspect the invention consists in a method of producing perfluoro-azabicyclodecane and its lower (1-2 C-atom) homologues which method comprises reacting quinoline or an alkyl quinoline with a higher-valent metal fluoride at 250.degree.-400.degree. C. in an inert reactor to produce a fully-fluorinated product. During fluorination a shift of bonds takes place so that the nitrogen atom in the product is in a tertiary position giving a principal product with 5- and 7-membered rings fused together.

By a "higher valent metal fluoride" we mean a metal fluoride in a higher valency state such as cobalt (III) fluoride CoF.sub.3 or CsCoF.sub.4 which is reduced to a lower valency state while acting as a fluorinating agent.

The product may be purified by fractional distillation and perfluoro-1-azabicyclo(5,3,0)decane has the following physical properties:

Boiling range 127.degree.-129.degree. C.

Refractive index at 22.degree. C. n.sub.D.sup.22 =1.3100

Specific gravity at 20.degree. C.=1.900

Pour point=-41.degree. to -42.degree. C.

Solubilities at 25.degree. C.

In a third aspect the invention consists in an oil-in-water emulsion comprising perfluoro-azabicyclodecane or a lower (1-2 C) homologue dispersed in an aqueous medium by means of a surface active agent. Preferably the surface active agent is non-ionic.

The invention will be further illustrated by the following Examples of the preparation of novel perfluoro-heterocyclic compounds in accordance with the invention.

In a typical experiment, quinoline (150 g) was passed over cobalt (III) fluoride (10 kg) in a paddle-stirred horizontal nickel reactor at 350.degree. (following the procedure in Advances in Fluorine Chemistry Vol. 1 p. 166) to give a crude liquid fluorocarbon (335 g) which was washed thoroughly with water and dried over calcium oxide. Fractional distillation of combined product from several fluorinations (in a 4 ft glass column with nickel Dixon gauzes) gave perfluoro-1-azabicyclo(5,3,0)decane, C.sub.9 F.sub.17 N, as a colourless liquid b.p. 127.degree.-129.degree. (24.5% by wt. of the crude product). Neighbouring fractions contain some C.sub.9 F.sub.17 N mixed with other compounds.

2-Methyl quinoline was fluorinated over cobalt (III) fluoride at 320.degree.-330.degree. C., following the procedure described in Example 1. The product was a clear colourless liquid (typically 212 g of product from 100 g of input). Product from several fluorination runs was combined, washed and dried over CaO and MgSO.sub.4. The mixture was fractionally distilled (3 ft glass column with nickel Dixon gauzes). Fractional distillation gave a compound (b.p. 146.degree.-148.degree. C.) for which .sup.19 F n.m.r. indicates the absence of N--CF.sub.3 groups and the presence of a C--CF.sub.3 group, which is consistent with a --CF.sub.3 group attached to a carbon atom adjacent to the bridgehead nitrogent atom. No N--F bonds were detected (from n.m.r.) and from its infra red spectrum the compound is clearly saturated. The relative molecular mass (by mass spectrometry) was 495 (C.sub.10 F.sub.19 N). The product is base-stable and its structure is consistent with perfluoro-1-aza-2-methyl(5,3,0)decane.

The utility of the compounds according to the invention as a blood-substitute or a perfusate for organ preservation will be illustrated as follows.

Potential use as an oxygen carrier for medical applications in comparison with perfluorodecalin (see for example U.S. Pat. No. 4,186,253).

To 10 ml. of perfluoro-1-azabicyclo(5,3,0)decane (ABCD) was added 10 ml. of solution made by dissolving 8.0 g of a non-ionic, polyoxyethylene-polyoxypropylene surfactant ('Pluronic F68', RTM) in 220 ml. of deionised water. The mixture was emulsified for a few minutes using a high speed mixer to form an emulsion having the appearance of diluted milk. On standing at room temperature overnight, there was a minor amount of separation ('creaming') of the emulsion.

In a comparison test, an emulsion was formed using perfluorodecalin. An emulsion of similar appearance to that formed with ABCD required about 10 minutes emulsification. On standing over-night pronounced creaming occurred.

A portion of 20 ml. of ABCD was degassed by boiling and cooled to 20.degree. C. while being bubbled with oxygen gas. The oxygen-saturated liquid was then degassed under vacuum and the gas evolved was collected and its volume measured at a known temperature and pressure. After allowing for the vapour pressure of the fluorocarbon, the solubility of oxygen was calculated to be in the range 45.+-.10 mls of O.sub.2 (at 760 mm Hg & 0.degree. C.) per 100 ml. of fluorocarbon. The solubility of oxygen in ABCD is thus adequate to permit the use of this fluorocarbon as an oxygen carrier for medical use.

ABCD was evaluated as candidate for an artificial blood substitute from the aspects of toxicity, feasibility of emulsification and excretion rate from the organs.

Wistar strain male rats administered with ABCD emulsion (dose as ABCD: 4 g/kg) gained weight favourably.

In order to evaluate the feasibility of emulsification, ABCD was emulsified with yolk phospholipids by using a Manton-Gaulin homogenizer and the stability to heating at 100.degree. C. for 30 minutes and storage at 4.degree. C. and 25.degree. C. for 2 weeks were examined. The emulsion was acceptably stable over these periods.

ABCD was very rapidly eliminated from the organs. 2 weeks after injection only trace amounts of ABCD were detected in all organs.

Gas chromatography results--rats injected with emulsion of ABCD (0.32 ml. fluorocarbon per 100 gm body weight). The following residual fluorocarbon concentrations were observed. (In mg. fluorocarbon/gm tissue).