SynopsisPolynucleotide analogs with a polyethylenimine backbone and optically active thymine-and adenine-containing pendants and their model compounds were synthesized. The pendants were prepared by the addition reaction of the nucleic acid base to ethyl crotonate. The ammonium salt of 3-(adenin-9-yl)butyric acid was employed to replace its free acid for the formation of diastereomeric salt with brucine. Fractional crystallization of the diastereomeric salt generates the partially resolved enantiomers. The solubility difference between the racemic mixture and its enantiomer was utilized to obtain the pure enantiomers. The active esters of the pendants were prepared. Grafting reactions were carried out by the reaction of active esters with PEI at room temperature. Completely grafted polymers were obtained.*Preliminary results are reported in J.Solvents were purified and dried as described in the literature. Thymine, adenine, ethyl crotonate, N-hydroxysuccinimide, diethylamine, and brucine dihydrate were purchased from Aldrich Chemical Co. and used without further purification. Linear polyethylenimine was obtained from hydrolysis of poly( N-propanoylethylenimine) M, = 500,000, obtained from Dow Chemical Co. Elemental analyses were carried out by Galbraith Laboratories, Inc., Knoxville, Tennessee. Melting points were determined on a Thomas-Hoover capillary melting point apparatus. Optical rotations were measured with a Perkin-Elmer 141 polarimeter at 25OC in a 10 cm cell. The 'H and I3C nuclear magnetic resonance spectra were obtained on a Bruker WM-360 or AM-300 spectrometer. The pH of the aqueous solution was determined using an Orion 701 pH meter.
Syntheses
Methyl 3-(Adenin-9-yl)butyrate (1)This compound was prepared following the general procedure for the preparation of methyl 3-(thymin-l-yl) butyrate.14 From 30 g of adenine there was obtained 55.9 (858, based on adenine) of methyl 3-(adenin-9-yl)butyrate, mp 168-169OC.
NH,), 4.98Methyl 3-(adenin-9-yl)butyrate (10 g, 4.2 mmol) was added to 100 mL of 5N ammonium hydroxide solution. The mixture was stirred at 70°C for 4 h. The water and excess ammonium hydroxide were removed by evaporation under reduced pressure. The residue was stirred with 300 mL of acetone for 4 h to yield 9.5 g (95%) of ammonium 3-(adenin-9-yl)butyrate, mp 232-234°C. N%), 6.89 (br,4H,NF4), 4.90 (m,lH,CHCH,), -2.68(m,2H,CH2), 1.49 'H-NMR (DMSO-d,): S 8.16, 8.12 (2S,2H,AdC2,, -H), 7.17 (S,2H, Ad-(d, 3H, CH,). ANAL. ( + ), ( -)-3-(Adenin-9-yl)butyriyric Acid (4,5)Ammonium butyrate (35.8 g, 0.15 mol) in 300 mL of water was added to 64.8 g (0.15 mol) of brucine dihydrate in 200 mL of methanol. The mixture was refluxed vigorously. The evolution of ammonia gas was detected immediately by placing moistened pH paper on top of the condenser. After refluxing for about 48 h (or until no more ammonia gas evolved) the solvents were removed by evaporation under reduced pressure. A stable adenine butyric acid-brucine
