SYNTHESIS AND CONFORMATIONAL STUDIES OF OXYTOCIN ANALOGS.

Abstract

The preparation of 11 new oxytocin analogs is described. The synthesis of the protected peptides were performed using solid phase peptides synthetic methodology. The protected peptides were deprotected and cyclized using sodium in liquid ammonia followed by aqueous potassium ferricyanide treatment. The purification of each peptide was accomplished using partition chromatography followed by gel filtration. Final purity was checked using high-performance liquid chromatography. Several amino-acid derivatives were prepared and incorporated as racemates into the synthetic peptides. The synthetic diastereomeric peptides were separated and purified by high pressure liquid chromatography using aqueous trifluoroacetic acid:acetonitrile mixtures. The oxytocin analogs prepared in this dissertation were divided into 2 classes: oxytocin agonists and oxytocin antagonists. The oxytocin agonist analogs prepared are [2-cycloleucine]oxytocin and [8-cycloleucine]oxytocin. The oxytocin antagonists described in this dissertation are [Pen¹,Cle²]oxytocin, [Pen¹,Cle⁸]oxytocin, [Pen¹,L-TyrMe²,Thr⁴,Orn⁸]oxytocin, [Pen¹,L-TyrEt²,Thr⁴,Orn⁸]oxytocin, [Pen¹,D-TyrEt²,Thr⁴,Orn⁸]oxytocin, [Pen¹,L-PheMe²,Thr⁴,Orn⁸]oxytocin, [Pen¹,L-PheEt²,Thr⁴,Orn⁸]oxytocin, [Pen¹,D-PheMe²,Thr⁴,Orn⁸]oxytocin and [Pen¹,D-PheEt²,Thr⁴,Orn⁸]oxytocin. A conformational study of the synthetic peptides was also undertaken in order to determine possible solution conformations for the various peptides. Two biophysical methods were used in the conformational study of these peptides; they include nuclear magnetic resonance spectroscopy (H-1 and C-13) and circular dichroism spectroscopy. Two somewhat different solution conformations were discovered for peptides containing all L-amino acids and for peptides containing a D-amino acid residue in position 2. A possible correlation between biological potency and observed solution conformation is suggested; the proposed models may aid in the design of more potent peptide inhibitor analogs.