Aminolysis of low‐molecular‐weight and polymeric 4‐nitrophenyl esters

Abstract 4‐Nitrophenyl methacrylate (1a), 4‐nitrophenyl esters of some N ‐methacryloyl‐ω‐amino acids (1b −d) and 4‐nitrophenyl esters of N ‐acetyl‐ and N ‐methacryloyltryptophane (2a and 2b) were prepared and characterized. Copolymers of 1 a −d and 2 b with N ‐2‐hydroxypropylmethacrylamide (HPMA), N ‐isopropylmethacrylamide (iPMA) and N ‐ethylmethacrylamide (EMA) were also prepared. The 4‐nitrophenyl ester content of the copolymers was determined spectrophotometrically from their UV absorption and from the UV absorption of the 4‐nitrophenolate ion which is released upon hydrolysis of the active esters with 0,1 M sodium hydroxide. The difference between these values depends on both the type of polymerizable active ester used and the comonomer. The proportion of non‐hydrolyzable structure is especially high in the case of copolymers containing 4‐nitrophenyl esters of the methacryloylated α‐amino acids 1b and 2b . The formation of non‐hydrolyzable structures is likely due to side reactions which occur during polymerization. The polymers prepared by copolymerization of the polymerizable 4‐nitrophenyl esters were not found to be suitable for the preparation of polymeric fluorescent probes by a chemical modification route. It was found that the rate of aminolysis of low‐molecular‐weight and polymeric activated esters increases with increasing the number of methylene groups in the N ‐(ω‐aminoalkyl)‐5‐dimethylamino‐1‐ naphthalenesulfonamides (dansylamines) 3a–f .