Chloramphenicol Derivatives Antigens and Antibodies

The following examples are offered by way of illustration and not by way of limitation.

All temperatures not otherwise indicated are centigrade. Percents and parts not otherwise indicated are by weight, except for mixtures of liquids which are by volume. Abbreviations which are employed are as follows: THF-tetrahydrofuran; tlc--thin layer chromatography; h--hour; DCC--dicyclohexyl carbodiimide; NHS--N-hydroxy succinimide; HOAc--acetic acid; BSA--bovine serum albumin; EDAC--ethyl dimethylaminopropyl carbodiimide.

A. A solution of oxalyl chloride (7.94 g, 62.5 mmol) and adipic acid monomethylester (4.0 g, 25 mmol) in benzene (20 ml) was heated to reflux under argon for 30 min, then allowed to stir over night under argon for 16 h. The reaction mixture was distilled at slightly reduced pressure to remove benzene and oxalyl chloride, then at 73.degree. and 0.2 mm to afford 4.46 g (100%) of a colorless oil.

B. To a solution of N-1,3-dihydroxy-1-(p-anilino)propyl dichloroacetamide (703 mg, 2.39 mmol) in THF (17 ml) and Et.sub.3 N (0.5 ml) at 0.degree. under argon was added adipic acid chloride monomethylester (853 mg, 4.78 mmol) in THF (3 ml) dropwise over 30 min and the reaction was allowed to stir warming to room temperature over 90 min. Tlc indicated that two new products, bisacylated and monoacylated had been formed in nearly equal amounts. The reaction mixture was poured into ice/HCl (pH=1), extracted with ethyl acetate (3.times.100 ml), washed (saturated brine), dried (Na.sub.2 SO.sub.4) and concentrated. Nmr confirmed that the two spots on tlc were due to mono and bisacylated starting material. This reaction mixture was hydrolyzed without further purification.

C. To a solution of the above mixture (1.29 g, 2.23 mmol) in methanol (15 ml) at 0.degree.-4.degree. was added an aqueous 5% sodium carbonate solution (18 ml) dropwise over 1 h. Stirring at 4.degree. was continued for 27 h. Tlc indicated incomplete hydrolysis, therefore 5% sodium carbonate (4.5 ml) was added dropwise and the reaction was allowed to stir at 4.degree. for an additional 15.5 h. At this time an additional 4.5 ml of 5% sodium carbonate was added and stirring was continued for 4 h. The reaction mixture was poured into ice/HCl (20 ml), was made acidic (pH=1), extracted with ethyl acetate (4.times.100 ml), washed (brine), dried (Na.sub.2 SO.sub.4) and concentrated to afford 1.05 grams of crude material. Preparative thin layer chromatography on silica gel plates eluting with methylene chloride (83%) and methanol (17%) afforded 160 mg (16%) of the mono-N-adipoyl product, and 309 mg of partially hydrolyzed material. The latter was redissolved in methanol (5 ml) at 4.degree. and to it was added 5% sodium carbonate solution (5.5 ml). This reaction mixture was allowed to stir for 4 days, was quenched with ice/HCl (pH=1), extracted with ethyl acetate, dried (Na.sub.2 SO.sub.4) and concentrated. Preparative tlc on silica eluting with methylene chloride/methanol/dichloroacetic acid (84/16/0.1, v/v/v) afforded 160 mg (16%) of the desired product.

D. To a solution of the above product (C) (160 mg, 0.38 mmol) in dry THF (20 ml) under argon at 0.degree. was added DCC (165 mg, 0.8 mmol) and NHS (46 mg, 0.4 mmol) and the reaction mixture was allowed to stir for two days. Tlc (CH.sub.2 Cl.sub.2 /MeOH/HOAc, 85/15/0.1,) indicated incomplete reaction and therefore DCC (83 mg, 0.4 mmol) and NHS (23 mg, 0.2 mmol) were added. Stirring at 0.degree.-4.degree. was continued for 24 h. at which time the reaction mixture was filtered, evaporated, washed with hexane, evaporated, dissolved in THF (10 ml) and added dropwise to a solution of BSA in phosphate buffer (20 ml) (pH=8.5) at 0.degree. and the reaction was allowed to stir for 30 h. Centrifugation at 10 K and 4.degree. for 30 min. followed by dialysis against water (1.times.4L), followed by Sephadex G-25 (100 g, 500 ml) chromatography, then followed by dialysis against water afforded 449 mg (88%) of protein conjugate. The hapten number, determined by UV extinction coefficients was found to be between 21 and 25 (.lambda..sub.max =246).

1-p-(Adipamidophenyl)-2-dichloroacetamido-1,3-propanediol (0.0053 g), 0.0018 g of NHS and 0.0029 g of EDAC were weighed into a dry 2-necked flask. After further drying the flask and its content overnight, 250 .mu.1 of dimethylformamide was added into the flask and the solution formed was stirred for four hours at 25.degree. C. Sixty-five .mu.1 of this solution was slowly added over a period of 5.25 hours to a 4.degree. C. solution containing 0.6 mg of glucose-6-phosphate dehydrogenase (Beckman Co., Fullerton, Ca.), 30 mg glucose-6-phosphate disodium (Sigma Co.) and 20 mg of nicotinamide adenine dinucleotide reduced (Sigma Co.) in 0.5 ml of 0.055M Tris buffer, pH 8, and 0.2 ml of carbitol. The pH of the reaction mixture throughout the 5.25 hour period was maintained in the range of 8.5 to 9.5 using 0.1N sodium hydroxide. At the end of the reaction period, the reaction mixture was chromatographed on a 19.times.1.9 cm column of Sephadex G-50 (Pharmacia, Piscataway, N.J.) and eluted with 0.055M Tris buffer, pH 8, containing 0.05% sodium azide and 0.005% thimerosol. 1.4 ml fractions were collected and those fractions containing high enzyme activity (usually fractions 7 to 10) were pooled and were used as the adipamido-chloramphenicol glucose-6-phosphate dehydrogenase conjugate.

The compositions prepared above were used in an assay for chloramphenicol. The assay employed the following reagents:

Protocol: 50 .mu.1 of the sample is drawn up into a diluter and dispensed with 250 .mu.1 of the assay buffer into a 1 ml Croan cup. A 50 .mu.1 aliquot of the diluted sample is drawn up and dispensed with a 250 .mu.1 portion of assay buffer into a second Croan cup. Into the second Croan cup is introduced 50 .mu.1 of the antibody reagent with 250 .mu.1 of the assay buffer, followed by the addition of 50 .mu.1 of the enzyme reagent and 250 .mu.1 of the assay buffer. Immediately after the enzyme addition, the entire sample is aspirated into the flow cell. After 15 sec. a first reading is taken, followed by a second reading after a 30 sec. interval. The results are reported as the difference in absorbance .times.2.667.

Four sheep were immunized with the antigen according to Example I. The antisera produced at the C bleed were tested for optimal assay response (O.D.) and for effective titer. The optimal assay response is the optimal separation in O.D. units between 2.5 .mu.g/ml and 40 .mu.g/ml chloramphenicol calibrators. This response shows the best range of the standard curve obtainable in accordance with the above described protocol. The larger the optimal assay response, the better the precision and accuracy. Effective titer is the amount of antiserum required per assay to give the optimal assay response. The higher the titer, the lower the required quantity of antiserum, the less expensive the assay production costs and the less extraneous material introduced into the assay medium. The following table reports the results of the four antisera.

Cross reactivity was determined against metabolites of chlor amphenicol as well as other drugs. Of the three known metabolites of chloramphenicol, 1-p-nitrophenyl-2-amino-1,3-propanediol; 1-p-aminophenyl-2-dichloroacetamido1,3-propanediol; and 1-p-aminophenyl-2-amino-1,3-propanediol, only the second metabolite showed significant activity, which is defined as the concentration of a compound which, when spiked into a 15.mu.g/ml control, will give a response in the assay equal to the response of 130% (i.e. 19.5.mu.g/ml) of the concentration of the 15.mu.g/ml control, the cross reactivity concentration for the second compound was 2 .mu.g/ml. Besides this metabolite, the chloramphenicol/succinate salt and thiamphenicol showed similar cross reactivity. Based on an independent study of a comparison between the above assay and HPLC with patient samples, which showed good correlation statistics between the two techniques, the effect of the cross reactivity on the subject assay to correctly quantitate chloramphenicol is believed to be minimal.

The compositions of the subject invention provide for reagents which provide a sensitive accurate assay for chloramphenicol, distinguishing chloramphenicol from closely related metabolites. The anitgenic conjugate provides for the efficient production of antibodies having high affinity and high titer for chloramphenicol. The combination of the antibodies and enzyme conjugates result in an accurate rapid assay for chloramphenicol in serum.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.