ETHER ISONITRILES AND RADIOLABELED COMPLEXES THEREOF

Abstract: Ether-substituted isonitriles, Tc99m com­ plexes thereof, and processes for myocardial tissue radioimaging using the Tc99m complexes.

Description: RELATED APPLICATION This application is a continuation-in-part of copending application U.S. Serial No. 8l2,470, filed December 23, l985. FIELD OF THE INVENTION This invention relates to novel ether-substi­ tuted isonitriles, radiolabeled complexes of these isonitriles, and methods of using the radiolabeled complexes for myocardial imaging. BACKGROUND OF THE INVENTION Isonitrile complexes of various radionuclides and their use as imaging agents have been described by Jones et al. U.S. Patent 4,452,774 issued June 5, l984. The complexes described by Jones, et al are of the general formula: [A((CN) x R) y B z B′ z′ ] n in which A is a radionuclide selected from radioactive isotopes of Tc, Ru, Co, Pt, Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd, Nb, and Ta, for example 99m Tc, ⁹⁹Tc, ⁹⁷Ru, ⁵¹Cr, ⁵⁷Co, ¹⁸⁸Re and ¹⁹¹Os; (CN) x R is a mono­ dentate or polydentate isonitrile ligand bonded to the radionuclide through the carbon atom of the CN group; R is an organic radical; B and B′ are independently selected from other ligands well known to those skilled in the art that result in isonitrile com­ plexes, including solvents such as water, chloro and bromo groups, and ligands comprising one or more neutral donor atoms capable of forming bonds with said radionuclide; x and y are each independently integers from l to 8; z and z′ are each independently 0 or an integer from l to 7; with the proviso that (xy)+z+z′ is less than or equal to 8; and n indicates the charge of the complex and can be 0 (neutral), or a positive or negative integer the value of which depends upon the valence state of A, and the charges on R, B and B′. Any desired counterion can be present as required by the charge on the complex with the proviso that such counterion must be pharmaceutically acceptable if the complex is to be used in vivo. In the above formula, R is an organic radical that can be aliphatic or aromatic and may be substi­ tuted with a variety of groups which may or may not be charged. When the organic radical R carries a charged substituent group, the charge on the resultant complex is the summation of the charges of the ligands (R, B and B′) and the charge of the radionuclide. Among the aromatic R groups which may be present are phenyl, tolyl, xylyl, naphthyl, diphenyl and substituted aromatic groups containing such substituents as halo, e.g., chloro, bromo, iodo or fluoro; hydroxy, nitro, alkyl, alkoxy, etc.; among the aliphatic R groups which may be present are alkyl, preferably containing l to 20 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-hexyl, 2-ethylhexyl, dodecyl, stearyl, etc. Substituent groups may also be present in the aliphatic groups, including among others the same substituent groups as those listed above for aromatic groups. The complexes described by Jones et al. are described as being useful for visualizing cardiac tissue, detecting the presence of thrombi in the lung and associated areas of blood perfusion deficits, studying lung function, studying renal excretion, and imaging bone marrow and the hepatobiliary system. In practice, the technetium complex of the simple hydrocarbon isonitriles such as t-butyliso­ nitrile preferred by Jones et al. have demonstrated somewhat high concentration in the lung and liver in humans. [Holman, et al., J. Nucl. Med. , 25 , l380(l984)]. The high early concentration of radio­ nuclide in the lung has required that imaging of the heart be delayed to allow the lung activity to clear before useful myocardial images can be obtained. In addition, the high concentration of radionuclide in the liver has made the detection of perfusion defects in the apical region of the myocardium more difficult. Clearly, the need exists for a more selective agent for myocardial imaging. SUMMARY OF THE INVENTION The subject invention provides novel ether-­ substituted isonitriles and diagnostic kits thereof, radiolabeled complexes of these isonitriles (preferably Tc99m), and diagnostic methods utilizing the radio­ labeled complexes. Although the general formula dis­ closed in Jones et al. U.S. 4,452,774 encompasses the radiolabeled, ether-substituted isonitrile complexes of this invention, such complexes are not specifically disclosed, and the dramatically superior imaging characteristics of these ether-substituted isonitriles are not contemplated by Jones et al. More specifically, one aspect of this inven­ tion provides novel ether-substituted isonitriles (and kits thereof) of the general formula I: CN-A-O-R I wherein: A is a straight or branched chain alkyl group and R is a straight or branched chain alkyl group, provided that the total number of carbon atoms in A plus R is 4 to 6, further provided that when the total number of carbon atoms in A plus R is 6 that the carbon atom alpha to the isonitrile group is a quaternary carbon and still further provided that A is not (CH₂)₃. Another aspect of this invention relates to novel radiolabeled complexes of these ether isonitriles of the general formula [M(CN-A-O-R)₆] where M is a radionuclide, most preferably Tc99M. Another aspect of this invention relates to the use of these radio­ labeled isonitrile complexes as myocardial imaging agents. DETAILED DESCRIPTION OF THE INVENTION The isonitriles of the present invention can be readily prepared by formylation of an alkoxyamine of the general formula II to give the corresponding formamide III , followed by dehydration to the isonitrile I . A variety of methods for the formylation and dehydra­ tion reactions are available in the literature and are well known to one skilled in the art of organic synthesis. The amines II can be prepared by a variety of methods known to one skilled in the art. In parti­ cular, the amines can be prepared by opening of an aziridine IV with an alcohol in the presence of an acid catalyst to give a mixture of the two amines V and VI which can be separated by distillation. Alternatively, the amines can be prepared from alkoxy­ esters VII wherein A′ is a hydrocarbon of 2 or 3 carbon atoms. Formation of the amide VIII by reaction with ammonia or ammonium hydroxide, followed by reduction with lithium aluminum hydride or another reducing agent known to reduce amides affords the amine IX . The amines II can also be prepared from the alkoxyesters X . Formation of the amide XI Proceeds as described above. The amide XI is subjected to the Hofmann Rearrangement to provide the amine II . Alternatively, the ether isonitriles can be prepared from amino alcohols XII by first reacting with a formylating agent, such as ethyl formate or formic acetic anhydride, to form the formamide-formate XIII . Conversion of the formamide-formate to the isonitrile-formate XIV is accomplished as already described for the other formamides. Mild aqueous hydrolysis of the formate yields the isonitrile-­ alcohol XV which can then be alkylated under standard alkylation conditions such as using sodium hydride and methyl halide such as iodide. The ether-substituted isonitriles useful in the practice of this invention include: CNCH₂CH₂CH₂OCH₃; CNCH₂CH₂CH₂OCH₂CH₃ CNC(CH₃)₂OCH₂CH₃; CNC(CH₃)₂OCH₃; CNCH₂C(CH₃)₂OCH₃; CNC(CH₃)₂CH₂OCH₃; CNCH(CH₃)CH₂OCH₃; CNCH(CH₃)CH₂OCH₂CH₃; CNCH₂CH(CH₃)OCH₃; CNCH₂CH(CH₃)OCH₂CH₃; CNCH(CH₃)CH(CH₃)OCH₃; CNCH₂CH(CH₃)CH₂OCH₃; CNCH₂CH₂CH(CH₃)OCH₃; CNCH₂CH₂OCH(CH₃)₂; CNCH₂CH₂OCH₂CH₃; CNCH(CH₃)OCH(CH₃)₂; CNCH₂CH(CH₂CH₃)OCH₃; CNCH(CH₂CH₃)CH₂OCH₃; CNCH(CH₃)CH₂CH₂OCH₃; CNC(CH₃)₂CH₂CH₂OCH₃. Specific examples of the preparation of these ether-­ substituted isonitriles are detailed below. Preparation l: Synthesis of l-methoxy-2-methylpropyl-­ 2-amine and 2-methoxy-2-methylpropyl-l-amine A. Synthesis of 2,2-Dimethylaziridine 2-Amino-2-methyl-l-propanol (l00 g. l.l2 mol) was dissolved in water (200 ml), and placed in a l000 ml round-bottom flask. Concentrated sulfuric acid (l00 g, l.l2 mol) was dissolved in water (200 ml) and was added to the amine solution. The resulting warm solution was distilled at atmospheric pressure. The temperature rose to l20°C, the pressure was reduced to aspirator pressure (approximately 25 mm Hg) and the distillation continued until the temperature of the distillate reached l50°C. The resulting brown gum was placed under vacuum (approximately l mm Hg) and heated to l70°-200°C for l.5 hours. Some charring occurred, and a solid resulted. The flask was then broken while encased in a protective pad, and the glass discarded. The solid was broken up using a hammer, and then a mortar and pestle, until it was mostly a fine powder and no pieces were larger than l/4" in diameter. The solid was added to a solution containing sodium hydroxide (l00 g, 2.5 mol) in water (l50 ml). The suspension was heated to ll0°C using a salt water bath and the solid slowly dissolved to form a black solu­ tion. The product distilled from this solution at 70-88°C onto sodium hydroxide pellets (25 g, 0.63 mol). By the end of the distillation a white precipitate had formed in the pot. After filtration through glass wool, the water layer was removed and the product was dried over sodium hydroxide, filtered, and dried over sodium metal. The product was distilled from sodium metal at 70-73°C to yield 46.2 g of a clear, colorless product (yield 58%). NMR(CHCl₃): δ 0.l (s, lH, NH), l.25 (s, 6H, CH₃), l.55 (s, 2H, CH₂) B. Synthesis of l-methoxy-2-methylpropyl-2-amine and 2-methoxy-2-methylpropyl-l-amine 2,2-Dimethylaziridine (27.68 g, 0.39 mol) was dissolved in freshly distilled methanol (50 g). This was cooled to -l0°C in an ice/acetone bath. Boron­ trifluoride bis-methanol complex (58.32 g, 0.44 mol) was dissolved in freshly distilled methanol (50 ml) and cooled in an ice/acetone bath to -l0°C. The cooled borontrifluoride solution was slowly added to the cooled aziridine solution over a 20 minute time period. The resulting solution was allowed to slowly warm to room temperature. The solution was stirred at room temperature for seven days while the production of the product was monitored by NMR. The solution was reduced in volume using rotary evaporation (25 mm Hg, 40°C) to approximately one-half original volume. Sodium methoxide in methanol (95.04 g of a 25% w/w solution, 0.594 mol) was added and a white precipitate formed. Diethylether (300 ml) was added and the precipitate was filtered. The still cloudy solution was distilled, and when the temperature reached 60°C, it was filtered again. The distillation was continued and a mixture of the two amines was obtained (l4.24 g, 35%). The two amines were separated using careful fractional distillations to yield pure 2-methoxy-2-­ methylpropyl-l-amine (b.p. l23-l24°C, NMR (CDCl₃): δ l.2 (s, 8H, NH₂CH₃), (s, 2H, CH₂), 3.3 (s, 3H, CH₃O) and l-methoxy-2-methylpropyl-2-amine (b.p. l03-l04°C). NMR (CDCl₃): δ l.l (s, 6H, CH₃), l.6 (bs, 2H, NH₂), 3.l (s, 2H, CH₂), 3.4. (s, 3H, CH₃O). Preparation 2: Synthesis of 2-methoxy-2-­ methylpropyl-l-amine A. Synthesis of Methyl 2-methoxy-2-methylpropanoate Dimethyl formamide (l00 ml) and tetrahydro­ furan (300 ml) were placed in a l000 ml three-neck round-bottom flask equipped with a thermometer, a mechanical stirrer, and a dropping funnel. An 80% dispersion of sodium hydride in oil (l9.80 g, 0.66 mol) was added to form a gray suspension. The suspension was cooled in an ice-water bath. Methyl hydroxyisobutyrate (70.8 g, 0.60 mol) was dissolved in tetrahydrofuran (50 ml) and added slowly to the cooled sodium hydride suspension while the temperature was held below l5°C. The resulting suspension was stirred for one hour. Methyl iodide (freshly distilled, l08.75 g, 0.75 mol) in tetrahydrofuran (25 ml) was slowly added to the cooled suspension. The addition took l.5 hours, during which the temperature was held below l5°C. The suspension was stirred and allowed to warm to room temperature for l5 hours. The suspension was poured into ethyl acetate (300 ml) and water (300 ml). The clear layers were separated and the aqueous phase was extracted with ethyl acetate (300 ml). The combined organic layers were decolorized with water (200 ml) containing sodium bisulfite (l0 g). The organic phase was separated and dried over magnesium sulfate. The solvent was mostly removed by rotary evaporation (25 mm Hg, 30°C). The resulting solution was distilled at atmospheric pressure and the product collected at l37-l46°C. The product was contaminated with DMF, but by NMR the yield of product was 48.8 g (6l%). NMR (CHCl₃) : δ l.4 (s, 6H, CH₃), 3.3 (s, 3H, CH₃O ether), 3.8 (s, 3H, CH₃O ester). B. Synthesis of 2-methoxy-2-methylpropanamide Methyl 2-methoxy-2-methylpropanoate (42.24 g, 032 mol, this had with it l0.6 g of DMF) was added to ammonium hydroxide (200 ml). This resulted in a two-phase system that was stirred at 25-30°C for l7 hours. The clear homogeneous solution that resulted was concentrated to a white precipitate by rotary evaporation (25 mm Hg, 50°C). The wet solid was dissolved in methylene chloride (200 ml). The water layer was separated and the methylene chloride layer passed through a plug of silica. The water layer was washed with methylene chloride (l00 ml) and this methylene chloride layer was also passed through the plug of silica. Finally, methylene chloride (l00 ml) was passed through the silica plug and the combined methylene chloride fractions were evaporated by rotary evaporation (25 mm Hg, 35°C) to give a white crystal­ line material. This was dried in vacuo to yield 29.5 g (79%). NMR (CDCl₃): δ l.4 (s, 6H, CH₃), 3.3 (9, 3H, CH₃O), 6.4 (very b, 2H, NH₂). C. Synthesis of 2-methoxy-2-methylpropyl-l-amine Lithium aluminum hydride (3.04 g, 0.08 mol) was added to a 250 ml dry two-neck round-bottom flask. The flask was kept under dry nitrogen at all times. Dry tetrahydrofuran (THF) (25 ml) was added and the suspension stirred. 2-Methoxy-2-methylpropanamide (8.l9 g, 0.07 mol) was dissolved in 80 ml dry tetra­ hydrofuran and added slowly to the lithium aluminum hydride suspension. The addition was just fast enough to maintain a gentle reflux. The addition took one-­ half hour and the resulting suspension was refluxed for an additional hour. The suspension was allowed to cool, 3 ml water was added dropwise with stirring, followed by 3 ml of l5% sodium hydroxide. Finally, 9 ml water was added and the warm suspension was stirred for l5 minutes. The white precipitate was filtered on a medium frit and washed repeatedly with THF. The combined THF fractions were distilled at atmospheric pressure. The THF was removed below 70°C. The product distilled at approximately l24°C. Yield: 4.l9 g (58%) NMR (CDCl₃): δ l.l5 (s, 8H, CH₃, NH₂), 2.6 (s, 2H, CH₂), 3.2 (s, 3H, CH₃O). Preparation 3: Synthesis of N-(2-methoxy-2-methyl­ propyl) formamide Formic acid (l9.2 g, 0.40 mol) and acetic anhydride (40.8 g, 0.40 mol) were combined and heated to 45-50°C for one hour and cooled to approximately 0°C in an ice/acetone bath. A solution of 2-methoxy-­ 2-methylpropyl-l-amine (36 g, 0.35 mol), precooled to approximately 0°C in an ice/ acetone bath was added slowly while keeping the temperature of the mixture below l2°C. After the addition was complete, the mixture was allowed to warm slowly to room temperature and was stirred at room temperature overnight. The solution was evaporated and the residue distilled at 97-l07°C/l-2 mm Hg. to give 43.2 g (94%). NMR (CDCl₃): δ l.2 (s, 6H, CH₃), 3.3 (m, 5H, CH₃O and CH₂), 6.6 (b, lH, NH), 8.2 (bs, lH, HCO). Preparation 4: N-[2-(l-methoxypropyl)]formamide Formic acid (l6.80g, 0.35 mol) and acetic anhydride (37.50g, 0.35 mol) were combined and heated at 45-50°C for l hour and cooled to approximately 0°C in an ice/acetone bath. 2-amino-l-methoxy propane (26.7g, 0.30 mol) was cooled in an ice/acetone bath to below 0°C. Formic acid (25ml) was slowly added to the cooled amine. The resulting solution was cooled further until it was below 0°C. The amine solution was added to the cooled formic-acetic anhydride solution and the resulting solution was stirred and allowed to slowly warm to room temperature overnight. The solutions was distilled under low pressure (∿lmm Hg) and the formic acid, acetic acid, and formic-acetic anhydride all distilled at low temperature. The product was distilled at 79-85°C to yield a clear, colorless oil. Yield 33.l3g, (94%). NMR (CHCl₃) δ l.05 (d, 3H, CH₃-C), 3.4 (M, 5H, CH₃O)CH₂O 4.2 (m, lH, CH), 6.8 (b, lH, N-H), 8.0 (b, lH, HC=O) Isonitrile Synthesis The following synthetic routes for preparation of 2-methoxy-2-methylpropyl-l-isonitrile, l-methoxy­ propyl-2-isonitrile, and 3-isonitrile-3-methyl-l-­ methoxybutane are also useful for the preparation of the other corresponding isonitrile versions of the ether compounds detailed above. l. Preparation of 2-methoxy-2-methylpropyl-l-­ isonitrile N-(2-methoxy-2-methylpropyl)formamide (l.97 g, 0.0l5 mol) was added to methylene chloride (23 ml). Triethylamine (4.04 g, 0.040 mol) was added and the clear solution was cooled in an ice/water bath. Disphosgene (trichloromethyl chloroformate, l.68 g, 0.0085 mol) was dissolved in methylene chloride (l0 ml) and slowly added to the cooled formamide solution (45 minutes). The suspension was allowed to warm to room temperature with stirring for two hours. The suspension was then poured into water (25 ml) con­ taining sodium dihydrogen phosphate (6.90 g, 0.05 mol). The methylene chloride layer was separated and dried over sodium carbonate. The solution was then distilled under reduced pressure (25 mm Hg), product distilled at 56-59°C, 0.530 g (3l% yield). NMR (CDCl₃): δ l.3 (s, 6H, CH₃), 3.25 (s, 3H, CH₃O), 3.4 (m, 2H, CH₂). 2. Preparation of l-methoxypropyl-2-isonitrile N-[2-(l-methoxypropyl)]formamide (ll.7g, 0.l0 mol) was dissolved in methylene chloride (l25 ml). Triethylamine (30.30g, 0.30 mol) was added and the clear solution was cooled in an ice/ water bath. Diphosgene (ll.88g, 0.06 mol) was dissolved in methylene chloride (40 ml). The diphosgene solution was added slowly to the cooled formamide solution. The resulting suspension was stirred and allowed to slowly warm to room temperature for l? hours. The suspension was poured into water containing sodium carbonate (42.4g, 0.40 mol). The methylene chloride layer was separated and washed with water containing sodium dihydrogen phosphate (55.2g 0.40 mol). The methylene chloride layer was separated and dried over sodium carbonate (anhydrous). The solution was filtered and distilled at aspirator pressure (∿25mm Hg). The product distilled at 63-66°C. Yield 5.83 g (58.8%). NMR (CDCl₃) δ l.05 (6 equivalent peaks, 3H, CH₃C), 3.0 (s, 3H, CH₃O), 3.l (m, 2H, CH₂), 3.5 (m, lH, CH). 3. Synthesis of 3-isonitrilo-3-methyl-l-methoxybutane A. Synthesis of 3-formamido-3-methyl-l-butanol 3-Amino-3-methyl-l-butanol (20.60 g, 0.20 mol) was added to ethyl formate (29.60 g, 0.40 mol), and the resulting clear solution was heated to reflux under nitrogen for 2 hours, and then allowed to cool to room temperature. The ethyl formate and ethanol by-product were removed by rotary evaporation (35°C, 25 Torr). The resulting oil was dried under vacuum (25°C, 0.l Torr) to yield 25.86 g (99%). NMR (CDCl₃): l.4 (d, 6H, CH₃), 2.0 (m, 2H), C-CH₂), 3.9 (m, 2H, O-CH₂), 7.l (bs, lH, NH), (m, lH, HCO). B. Synthesis of 3-formamido-3-methyl-l-butyl formate Formic acid (6.90 g, 0.l5 mol) was added to acetic anhydride (l5.30 g, 0.l5 mol) and warmed to 45-50°C for one hour on a water bath. The resulting solution was cooled to below 0°C in an ice/acetone bath. 3-Formamido-3-methyl-l-butanol (l3.l0 g, 0.l0 mol) was added and the solution allowed to slowly warm to room temperature with stirring (l6 hours). The solution was distilled under vacuum (l Torr, l05-ll0°C) to yield l2.43 g (78%). NMR (CDCl₃): l.4 (s, 6H, CH₃), 2.l (t, 2H, C-CH₂), 4.2 (t, 2H, O-CH₂), 6.0 (bs, lH, NH), 8.0 (m, 2H, HCOO). C. Synthesis of 3-isonitrilo-3-methyl-l-butyl formate 3-Formamido-3-methyl-l-butyl formate (ll.l3 g, 0.07 mol) and triethylamine (2l.2l g, 0.2l mol) were dissolved in methylene chloride (350 ml). The resulting solution was cooled in an ice/water bath under nitrogen. Trichloromethyl chloroformate (diphosgene) (8.32 g, 0.042 mol) was dissolved in methylene chloride (50 ml) and added dropwise to the stirred, cooled formamide solution over 30 minutes. The resulting suspension was stirred and allowed to warm to room temperature over 90 minutes. Water (250 ml) containing sodium carbonate (23 g, 0.22 mol) was added to the suspension and the lower organic layer was separated. This was washed with water (250 ml) containing sodium dihydrogen phosphate (30 g, 0.22 mol). The resulting organic layer was dried over sodium carbonate (anhydrous, 25 g). The solution was filtered and distilled under aspirator pressure (25 Torr). The solvent distilled below room temperature and the product distilled at 96-l02°C to yield 9.22 g (93%). NMR (CDCl₃): l.5 (m, 6H, CH₃), 2.0 (m, 2H, C-CH₂), 4.4 (t, 2H, O-CH₂), 8.0 (s, lH, HCO). D. Synthesis of 3-isonitrilo-3-methyl-l-butanol Sodium bicarbonate (8.40 g, 0.l0 mol) and sodium carbonate (l0.60 g, 0.l0 mol) were dissolved in water (200 ml). 3-Isonitrilo-3-methyl-l-butyl formate was added and stirred vigorously. The cloudy solution was allowed to sit for 5 hours at room temperature. Sodium chloride (l0 g, 0.l7 mol) was added and the suspension stirred for l5 minutes. The suspension was extracted with ethyl acetate (3 × l00 ml). The combined organic layers were dried over sodium carbonate (25 g), filtered, and distilled at aspirator pressure (25 Torr). The product distilled at l20°C to yield 5.38 g (74%). NMR (CDCl₃): l.5 (m, 6H, CH₃), 2.0 (m, 2H, C-CH₂), 3.0 (bs, lH, OH), 4.0 (t, 2H, O-CH₂). E. Synthesis of 3-isonitrilo-3-methyl-l-methoxybutane 3-Isonitrilo-3-methyl-l-butanol (l.l3 g, 0.0l mol) was dissolved in tetrahydrofuran (20 ml) and dimethylsulfoxide (2 ml). Iodomethane (l.42 g, 0.0l) was added and the solution stirred at room temperature for 5 minutes. Sodium hydride (80% dispersion in oil, 0.30 g, 0.0l mol) was added in small portions over a l5 minute period. The resulting suspension was stirred for 90 minutes. Water (l5 ml) was added and the organic layer separated. The water layer was extracted with ethyl acetate ( 2 × 20 ml), and the combined organic layers were dried over sodium carbonate (2 g), filtered, and distilled at aspirator pressure (25 Torr). The product distilled at 80-90°C to yield 0.48 g (38%). NMR (CDCl₃): l.5 (m, 6H, CH₃), 2.0 (m, 2H, C-CH₂), 3.4 (s, 3H, CH₃), 3.6 (t, 2H, O-CH₂). The desired radiolabeled, ether-substituted isonitrile complexes are prepared by admixing the isonitrile with the radioactive metal in suitable media at temperatures from room temperature to reflux temperatures or even higher. The desired labeled isonitrile complexes are isolable and can be obtained in high yields. In some cases the isonitrile can itself act as a reducing agent thus eliminating the need for an additional reducing agent. Additional reducing agents, when required or desired to speed up the reaction, are well known to those skilled in the art. Examples of such well-known reducing agents include stannous salt (often used in the form of kits), formamidine sulfinic acid, sodium dithionite, sodium bisulfite, hydroxylamine, ascorbic acid, and the like. The reaction is generally complete after about l minute to about 2 hours, depending upon the particular reagents employed and the conditions used. In the case of technetium such as, for example ⁹⁹Tc or 99m Tc, an isonitrile complex is preferably made by mixing an appropriate reducing agent (capable of reducing technetium in aqueous medium) and the appropriate ether-substituted isonitrile then added pertechnetate. Alternatively, the ether-substituted isonitrile and pertechnetate are mixed, then reductant added. The isonitrile technetium complexes prepared in accord with this invention can also be prepared from preformed technetium complexes having oxidation states for technetium of, for instance, III, IV or V, by treating these preformed complexes with an excess of ether-substituted isonitrile under suitable conditions. An excess of the ether-substituted isonitrile, up to l00 fold molar excess or more, and an excess of reducing agent, can be used in the complexing reaction to ensure maximum yield from the technetium. Following the reaction, the desired complex can be separated from the reaction mixture, if required, for example by crystallization or precipitation or by conventional chromatography or ion exchange chromatography; see U.S. 4,452,774, supra, the disclosure of which is hereby incorporated by reference. Kits in accord with the present invention comprise a sterile, non-pyrogenic, ether-substituted isonitrile ligand and, if required, a quantity of a reducing agent for reducing a preselected radionuclide. Preferably, such kits contain a predetermined quantity of a sterile, ether-substituted isonitrile ligand and a predetermined quantity of a sterile reducing agent capable of reducing a predetermined quantity of the preselected radionuclide. It is also preferred that the isonitrile ligand and reducing agent be lyophilized, when possible, to facilitate storage stability. If lyophilization is not practical, the kits can be stored frozen or in solution at room temperature. The ether-substituted isonitrile and reducing agent are preferably contained in sealed, non-pyrogenic, sterilized containers. The ether-­ substituted isonitrile in such kits can be in the form of a non-radioactive metal adduct such as those described in copending and commonly assigned U.S.S.N. 762,392, and in published European Patent Application l83, 555, published June 24, l986, the disclosures of which are hereby incorporated by reference. The displaceable metals useful in the preparation of such metal-adducts are selected from the class consisting of Cu, Mo, Pd, Co, Ni, Cr, Ag, Rh (672,392) and Zn (European l83,555), and can be readily be prepared by admixing a complex of the displaceable metal and the ether-substituted isonitrile ligand in a suitable media at temperatures from room temperature to reflux temperature or even higher. The reaction is generally complete after about l minute to about 2 hours, depending upon the reagents employed and the condi­ tions used. The choice of radionuclides will depend on the use. Of course, because of availability of Tc99m generators, such radionuclide is especially preferred. The following exemplifies the unexpected superiority of the ether-substituted isonitriles of the subject invention over the simple hydrocarbon isonitriles preferred by Jones et al. (U.S. 4,452,774). EXAMPLE The following Tc99m complexes were prepared: Complex A: [ 99m Tc(C X NC(CH₃)₂CH₂OCH₃)₆]⁺ Complex B: [ 99m Tc(C X NCH₂C(CH₃)₂OCH₃)₆]⁺ Complex C: [ 99m Tc(C X NCH(CH₃)CH₂OCH₃)₆]⁺ T-butyl isonitrile complex (comparative): [ 99m Tc(C X NC(CH₃)₃)₆]⁺ These technetium complexes were prepared using standard labeling conditions similar to those reported by Jones et al. The isonitrile (3-5 ml) was dissolved in ethanol (l ml) in a l0 cc serum vial and the vial was sealed and l00-l50 mCi of 99m TcO obtained by elution of a ⁹⁹Mo/ 99m Tc radionuclide generator was added. Sodium dithionite (0.5 ml of a solution of 20-25 mg of l0 ml of distilled water) was added and the vial was placed in a l00° water bath for l5 minutes. After cooling to room temperature, l ml of water and l ml of methylene chloride were added and the product was extracted into the methylene chloride. The organic layer was evaporated and the product was taken up in ethanol. The purity of the final product was determined by thin layer chromatography on Whatman C-l8 reversed-phase plates using a solvent mixture containing 22% 0.5 M aqueous ammonium acetate, 66% methanol, 9% acetonitrile, and 3% tetrahydrofuran or high pressure liquid chromatography on a Brownlee C-8 reversed-phase column (5 mm) and a solvent system consisting of 0.05 M aqueous ammonium sulfate and methanol with a linear gradient of 0-90% methanol over 20 minutes with a one minute delay from injection. The complexes were evaluated by determining the biodistribution of each in guinea pigs. Organ distribution of injected activity was determined at 5, 30, and l20 minutes post-injection. For each time-­ point, three guinea pigs were anesthetized with sodium pentobarbital (35 mg/kg ip) and injected with 0.l ml of test material via the jugular vein. The injected dose of 99m Tc isonitrile was l-2.5 mCi. Upon sacrifice, the organs were removed and radioactivity was measured using either a Capintec dose calibrator or gamma well counter. The heart, lungs and liver were weighed. The distribution of radioactivity in the heart, lung, and liver for the complexes are illustrated in the Table below. By reference to the heart/liver and heart/lung ratio, it can readily be seen that the technetium-99m complexes of this invention show marked superiority over the simple hydrocarbon isonitrile complex in exhibiting low uptake by the lungs and lower uptake by the liver (and/or fairly rapid washout from the liver) while maintaining high myocardial uptake. a = [ 99m Tc(C≡NC(CH₃)₂CH₂OCH₃)₆]⁺ b = [ 99m Tc(C≡NCH₂C(CH₃)₂OCH₃)₆]⁺ c = [ 99m Tc(C≡NCH(CH₃)CH₂OCH₃)₆]⁺ d = [ 99m Tc(C≡NC(CH₃)₃)₆]⁺

Claims: 1. A composition comprising an ether-­ substituted isonitrile of the formula CN-A-O-R wherein A is a straight or branched chain alkyl group and R is a straight or branched chain alkyl group, provided that the total number of carbon atoms in A plus R is 4 to 6, further provided that when the total number of carbon atoms in A plus R is 6 that the carbon atom alpha to the isonitrile group is a quaternary carbon, and still further provided that A is not (CH₂)₃. 2. A composition comprising CN(CH₂)₃OCH₃ in sterile, non-pyrogenic form. 3. The composition of claim l wherein the ether-substituted isonitrile is selected from CNCH₂C(CH₃)₂OCH₃, CNC(CH₃)₂CH₂OCH₃, CN(CH₂)₃OCH₂CH₃, CNCH(CH₃)CH₂OCH₃, CNCH(CH₃)CH₂OCH₂CH₃, CNCH₂CH(CH₃)OCH₃, CNCH₂CH(CH₃)OCH₂CH₃, CNCH(CH₃)CH(CH₃)OCH₃, CNCH₂CH(CH₃)CH₂OCH₃, CNCH₂CH₂CH(CH₃)OCH₃, CNC(CH₃)₂OCH₂CH₃, CNC(CH₃)₂OCH₃, CN(CH₂)OCH(CH₃)₂. CN(CH₂)₂OCH₂CH₃. CNCH₂CH(CH₂CH₃)OCH₃. CNCH(CH₂CH₃)CH₂OCH₃. CNCHCH₃OCH(CH₃)₂. CNCH(CH₃)CH₂CH₂OCH₃. CNC(CH₃)₂CH₂CH₂OCH₃. 4. The composition of any of claims l and 3 in sterile, non-pyrogenic form. 5. A kit comprising a predetermined quantity of the composition of anyone of claims l-4 and a predetermined quantity of a sterile, non-pyrogenic reducing agent capable of reducing technetium. 6. A composition of the formula [Tc99m(CN-A-O-R)₆] where (CN-A-O-R) is as defined in claim l. 7. A composition comprising any of the ether-substituted isonitriles of claims 2 and 3 complexed with Tc99m. 8. A process for preparing an ether-­ substituted isonitrile of the formula CN-A-O-R (I) wherein A is a straight or branched chain alkyl group and R is a straight or branched chain alkyl group, provided that the total number of carbon atoms in A plus R is 4 to 6, and further provided that A is not (CH₂)₃, and further provided that when the total number of carbon atoms in A plus R is 6 that the carbon atom alpha to the isonitrile group is a quaternary carbon, comprising: a) formylating an amine of the formula H₂N-A-OR (II) where A and R are defined above, by con­ tacting it with ethyl formate or formic­ acetic anhydride at a temperature of from about -5°C to the reflux tempera­ ture, to prepare a formamide of the formula H--A-O-R (III): b)dehydrating the formamide prepared in step (a) by contacting it in an inert solvent with diphosgene in the presence of a t-amine or phosphoryl chloride in the presence of an amine base at a temperature of from about -l0°C to room temperature; and (c)optionally reacting the isonitrile product of formula (I) with a complex of a non-radioactive metal selected from Cu, Mo, Pd, Co, Hi, Cr, Rh, and Zn to form an ether-substituted isonitrile metal adduct. 9.The process of claim 30 wherein the ether-substituted isonitrile or metal adduct thereof is optionally mixed with a reducing agent and made into a kit in sterile, nonpyrogenic form.

Inventors: BERGSTEIN PAUL LOUIS, SUBRAMANYAM VINAYAKAM, BERGSTEIN, PAUL LOUIS, SUBRAMANYAM, VINAYAKAM
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1986
Main classification: C07C291
IPC codes: C07C253, C07F3, C07C255, C07B59, G01N33, A61K51, C07D317, C07C291, C07F1, A61K103, C07F13