CARRIER DESIGN - SYNTHESIS AND CONFORMATIONAL STUDIES OF POLY(L-LYSINE) BASED BRANCHED POLYPEPTIDES WITH HYDROXYL-GROUPS IN THE SIDE-CHAINS

In the present study the development of a new series of branched polyp eptides that contain hydroxyl groups in side chains is reported. Serin e or threonine were attached by 1-hydroxy-benzotriazole catalyzed acti ve ester method to the N-terminals of oligo(DL-alanine) chains grafted to a polylysine backbone resulted in poly [Lys-(Ser(i)-DL-Ala(m))] (S AK) and poly[Lys-(Thr(i)-DL-Ala(m))] (TAK). Ser was coupled also direc tly to the epsilon-amino groups of polylysine followed by polymerizati on of N-carboxy-DL-alanine anhydride resulting oligo(DL-Ala) chain ter minals. Irt this way a reverse sequence was built up in the side chain corresponding to the poly [Lys-(DL-AIa(m)-Ser(i))] (ASK). The number of hydroxyl groups in the polymer was increased by the synthesis of a branched polypeptide with oligo (DL-serine) branches instead of oligo( DL-alanine) ones-poly[Lys-(DL-Ser(m))] (SK). Classification of solutio n conformations of branched polypeptides was carried out by CD spectro scopy performed in water solution of various pH values and ionic stren gths. Incorporation of single Ser residues in poly [Lys-(X-i)]-type po lypeptides markedly promotes the formation of ordered structure withou t resulting precipitation even in high salt concentration The presence of branches with multiple DL-Ser residues resulted in a slightly decr eased ability of the polypeptide backbone to adopt an ordered conforma tion. Comparison of the CD properties of the SAK-ASK pair demonstrates that these compounds are similar showing an increased tendency to for m an ordered spatial arrangement in solution at elevated pH or ionic s trength; however, differences in their CD spectra suggest that SAK has higher capability to form regular conformation under comparable condi tions. The replacement of Ser by the Thr residue in poly[Lys-(X-i-DL-A la(m))] induced a conformational transition and TAK exhibited a more h elical structure. These results might indicate that not only hydrophob ic or ionic attraction, but also H-bond interaction, can play a role i n the formation and/or stabilization of ordered conformation of branch ed polypeptides. Findings with the hydroxyl group containing polymers reported in this paper can also explain their prolonged shelf stabilit y and high water solubility. (C) 1997 John Wiley & Sons, Inc.