Poly-L-lysine derivatives

The reaction of the p-nitrophenyl esters with the polymer (4) was studied in dimethyl sulfoxide ( DMSO ) solution in the presence of triethylamine at 25°C. The poly-L-lysine derivatives obtained have different IR absorption spectra from those of the starting compounds, and have absorptions assigned to the nucleic acid bases. Poly( e,N-Ade-L-lysine )(5) was soluble in DMSO and ethylene glycol, and also in water below pH 3, where it was present as a protonated form. In dimethylformamide (... 

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 %(,] ). 

In relation to these works, the reaction of p-nitrophenyl esters with optically active poly( propyleneimine )(8) was studied at 25°C in DMSO solution according to the same procedure described for the case of poly-L-lysine derivatives. The poly( propyleneimine ) derivatives thus obtained have different IR and UV absorption spectra from those of the starting compounds, and show absorptions assigned to the nucleic acid bases. However, their contents determined by UV spectroscopy were substantially low as compared with the case of poly-L-lysine derivatives for (9) and (20), the base contents were below 30 and 50 %, respectively. The result was explained by a steric hindrance caused by methyl groups on the main chain of poly( propyleneimine ) ... 

Poly-L-lysine derivatives containing pendant nucleic acid bases were prepared by two different methods ... 

The poly-L-lysine derivatives containing pendant nucleic add bases can be prepared alternatively by using a polymer modification reaction69 (Scheme 19). Carboxyethyl derivatives of the bases were grafted onto poly-L-lysine by using the activated ester method . Poly-L-lysine was allowed to react in this case as trifluoroacetate71. ... 

The complex formation between the complementary poly-L-lysine derivatives was studied by UV spectroscopy in DMSO-EG72,76. Figure 24 shows mixing curves between PLL-A-67 and PLL-Ts with different nucleic add base contents. The complex formation between PLL-A-67 and PLL-T-93 can be dearly observed (Fig. 24 a). The overall stoichiometry of the complex based on the base units was about 1 2 (adenine thymine). As the adenine substituted poly-L-lysine contains 67% adenine units, the stoichiometry based on the polymer chain was about 1 1. The hypochromidty at this point was found to be 31%. 

From these facts, it is concluded that the polymer complexes are formed by specific base pairing between pendant adenine and thymine or uracil units of poly-L-lysine derivatives retaining their helical conformations (Fig. 26). The lowering of the base content in the polymers results in the decrease of the helical structure and also in the decrease of interactions with the complementary polymer. 

The stability and stoichiometry of the complex between polymers containing nucleic add bases are affected by the compatibility of the different base-base distances in the polymers, and also by the mutual penetration ability between the main chains. In the polyMAOA-polyMAOT system, for example, intramolecular base-base distances in each polymer are compatible and these polymers are able to penetrate each other38, Poly-L-lysine derivatives and vinyl polymers are apparently incompatible. This situation alone would lead to unstable complex formation where the overall stoichiometry would not be simple and thus could not reflect the stoichiometry on the binding site. 

We have recently reported that the low molecular weight poly-L-lysine derivatives are present in a random coil structure, in spite of the high content of the base, and are unable to form the polymer complex79. The formation of such a complex was not observed for the polyMAOA low molecular weight PLL-T system. This fact indicates that polyMAOA and PLL-T occurring in a random coil structure are incompatible and unable to penetrate each other. 

It has been reported that the helicity of poly-L-lysine derivatives decreases with decreasing base content and the formation of complexes between polymers is affected by their helical content79. Effect of helicity of poly-L-lysine derivatives on the complex formation ability has also been observed (Fig. 27). The value of hypochromicity tends to decrease remarkably with falling thymine content in PLL-Ts. The overall stoichiometry of the complex of polyMAOA - PLL-T-65 was obtained as 5 1 (adenine thymine) it does not reflect the stoichiometry at the binding site (the theoretical stoichiometry of the binding sites for the polyMAOA-PLL-T-65 system is 3 2 (adenine thymine)). 

Natural and synthetic polynucleotides are known to form polymer complexes by specific base-base interactions between nucleic acid bases. The synthetic nucleic acid analogs such as poly (methacryamide), poly-(ethyleneimine) and poly(L-lysine) derivatives containing nucleic acid bases were also found to form polymer complexes with polynucleotides by specific base-base interactions. Since the solubilities of these nucleic acid analogs in water were low, the specific interactions should be studied in organic solvents or water-organic mixed solvents, such as dimethyl sulfoxide, ethylene glucol, and water-propylene glycol. 

Three types of HPLC resins were prepared (1) nucleic acid base bonded silica gels Si-Thy (1), Si-Ura (2), Si-Cyt (3), Si-Ade (4), Si-Hyp (5), and Si-Gua (6) (Figure 2) (2) poly-L-lysine derivatives bonded silica gels Si-PLL Cbz (7), Si-PLL-Thy (8), and Si-PLL-Ade (9) (Figure 3) and (3) nucleoside bonded silica gels Si-Thd (10) and Si-Urd (11) (Figure 4). The detailed preparation methods of these silica gel derivatives will be shown elsewhere. ... 

Poly-L-lysine derivative bonded silica gel The poly-L-lysine derivative bonded silica gels having carbobenzyloxy (Si-PLL-Cbz 7), thymine (Si-PLL-Thy 8), and adenine (Si-PLL-Ade 9), were prepared as shown in Scheme 2 for Si-PLL-Thy (8). The nucleic acid base derivatives were grafted onto the poly-L-lysine having terminal carboxyl group, and were reacted with the APS-silica. 

Figure 3. Poly-L-lysine derivative bonded silica gels.

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