Nucleic acid base carboxyethyl derivatives

Carboxyethyl derivatives of the nucleic acid bases were grafted onto poly-L-lysine by using the activated ester method ( ). 

The contents of the nucleic acid bases in the poly-L-lysine derivatives were determined by UV spectra of the polymers after hydrolysis The polymers were hydrolyzed in 6 N-hydrochloric acid at 105°C for 24 hr, into lysine dihydrochloride and the carboxyethyl derivatives of the nucleic acid bases. The quantitative calculation was made relative to the standard sample of the carboxyethyl derivative of the nucleic acid bases. The analytical data are listed in Table 1. It was found that the thymine and uracil derivatives was completely substituted to polylysine. Low value in case of adenine base in the polymer may be attributed to the unstability of the activated ester, Ade-PNP (2), and may also be explained in terms of the steric interaction among bulky pendant groups of the polymer. When the poly-L-lysine containing about 50 mol % adenine units was again treated with Ade-PNP, the adenine unit content in the polymer increased up to 74 mol %(,] ). 

A series of new amino acid derivatives having pendant nucleic acid bases was prepared by the reaction of L-lysine and L-glutamic acid with the nucleic acid bases. These amino acids were further polymerized by using the N-carboxyamino acid anhydride ( NCA ) method. Alternatively, the nucleic acid base substituted poly-L-lysines were also prepared by using polymer reactions which include the reaction of carboxyethyl derivatives of the bases onto poly-L-lysine. Physico-chemical properties of the polymers obtained were given. 

The 2-carboxyethyl derivatives of nucleic acid bases were further grafted onto the monomeric graft polymers of L-a-amino acids on linear polyethylenimine (Table 18). The synthetic route to the graft polymers containing L-o-alanine and nucleic add bases is shown in Scheme 14. 

Starting from nucleic acid bases, the carboxyethyl derivatives of the nucleic acid bases were prepared by a Michael type addition reaction of ethyl acrylate followed by hydrolysis. The carboxyethyl derivatives of nucleic acid bases were reacted with ( )-a-amino T-butyrolactone hydrobromide to give v-hutyrolactone derivatives of nucleic acid bases. For the coupling reactions, pentachlorophenyl ester derivatives were used with imidazole as a catalyst.22... 

The grafting of nucleic acid base derivatives with a hydroxyl group onto poly(ethyleneimine) polymer backbone was also carried out by the activated ester method. Since the reactivity of the lactone is low, the direct reaction of the lactone derivative with poly(ethyleneimine) was not effective. Therefore, the lactone derivatives were at first hydrolyzed to the 3-hydroxybutyric acid derivatives, followed by condensation with poly(ethyleneimine) using the activated ester method. The grafting reaction was carried out in N,N-dimethylformamide, where a small amount of 4-pyrrolidinopyridine was added as an effective catalyst. Nucleic acid base contents of the polymers were determined by UV spectroscope of hydrolyzed samples. A quantitative calculations were made by using the corresponding carboxyethyl derivatives as standards. The nucleic acid base units (unit mol%) on the polymer are tabulated in Table 1. 

Nucleic acid base bonded silica gel The hypoxanthine bonded silica gel (Si-Hyp 5) was prepared by the reaction of the nucleic acid base derivatives with an 3-aminopropyl-silanized silica (APS-silica) Li-Chrosorb NH2, Merck) according to Scheme 1, and free silanol groups and amino groups were blocked by trimethylsilyl and acetyl groups, respectively. The carboxyethyl derivative of hypoxanthine (13) was prepared from the carboxyethyl derivative of adenine (12) according to the literature.The pentachlorophenyl activated ester (14) was reacted with the APS-silica to give the hypoxanthine bonded silica gel (Si-Hyp 5). The same method was applied to the preparation of nucleic acid base... 

Immobilization of the nucleic acid base derivatives on silica gel was confirmed by IR spectra and elementary analysis, and hydrolysis followed by measurement of UV spectra. The IR spectra for Si-Hyp suggested the presence of hypoxanthine units in the silica gel derivative. Quantitative determination of the content of hypoxanthine units in Si-Hyp was done by hydrolysis of the silica gel derivative followed by measurement of UV spectra bases on the spectra of the carboxyethyl derivative of hypoxanthine (14). The content of the hypoxanthine units in the silica gel derivative was about 1.5 x 10" mol/g. 

---