N-(9-Fluorenylmethoxycarbonyloxy)succinimide → HCID 90034845, compound

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Reaction Steps

As described in Helvetica Chimica Acta 1987, p. 1307-1311 by H. Hilpert the bis-ethylester protected racemic amino acid 3-(2-ethoxycarbonyl-4-pyridyl)-DL-alanine ethyl ester is prepared in the fourfold scale in comparison to the literature and yields 612 mg material. The compound gets characterized as described by 1H-NMR. The racemic amino acid 3-(2-ethoxycarbonyl-4-pyridyl)-DL-alanine ethyl ester is then dissolved in acetonitrile and treated with 0.1 N sodium hydroxide for 5 hours by vigorous agitating the mixture which hydrolyses preferentially the 2-Ethoxy group. The compound of interest 3-(2-carboxy-4-pyridyl)-DL-alanine ethyl ester is isolated from the mixture by preparative C4 reverse phase chromatography with a standard acetonitrile-water gradient with the eluting series of peaks 3-(2-carboxy-4-pyridyl)-DL-alanine, 3-(2-ethoxycarbonyl-4-pyridyl)-DL-alanine and 3-(2-ethoxycarbonyl-4-pyridyl)-DL-alanine ethyl ester. About 250 mg of a colorless oily lyophilisate can be received after freeze drying of all unified (2-carboxy-4-pyridyl)-DL-alanine ethyl ester containing fractions assigned as (2-carboxy-4-pyridyl)-DL-alanine ethyl ester by TLC (Chloroform/Methanol/Acetic Acid=9:1:1; UV detection). To tert.-butylate the 2-carboxy-group of (2-carboxy-4-pyridyl)-DL-alanine ethyl ester 240 mg is dissolved in 10 ml acetic acid tert.-butyl ester. A 1.2 molar extend of a 70% solution of perchloric acid in water is then added. After 5 days stirring under room temperature the mixture is extracted with ice cold 0.5 N hydrochloric acid. The extract is alkalized with 3N-sodium hydroxide and extracted with methylenchloride. After drying with magnesium chloride the organic phase is evaporated and the residual liquid is distilled which yields about 200 mg of 3-(2-tert.-butoxycarbonyl-4-pyridyl)-DL-alanine ethylester. To reversibly protect the amino group of 3-(2-tert.-butoxycarbonyl-4-pyridyl)-DL-alanine ethylester 180 mg of the compound is dissolved in 10 ml dioxane, then 300 mg Fmoc-OSu (Novabiochem/Merck) is dissolved in dioxane is added. Finally a twofold equivalent of Sodium bis-carbonate relative to 3-(2-tert.-butoxycarbonyl-4-pyridyl)-DL-alanine ethylester is added. After 3 hours of vigorous stirring the reaction volume is diluted with the same volume of 1 N sodiumhydroxyd solution to cleave the ethyl ester of the carboxy group. After 5 hours the volume of the reaction mixture is strongly reduced by evaporation. The whole phase is acidified and several times extracted by Acetic acid ethyl ester. After drying with Sodium sulfat the organic phase was completely evaporated to yield about 200 mg N-Fmoc-3-(2-t-butoxycarbonyl-4-pyridyl)-DL-alanine (D) as a colorless oil.

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