Secondary Structure of Cyclosporine in a Spray-Dried Liquid Crystal by FTIR

• Published in: Journal of pharmaceutical sciences Vol. 92; no. 9; pp. 1832 - 1843
• Main Authors: Stevenson, Cynthia L., Tan, Mandy M., Lechuga-Ballesteros, David
• Format: Journal Article
• Language: English
• Published: Hoboken Elsevier Inc 01.09.2003; Wiley Subscription Services, Inc., A Wiley Company; Wiley; American Pharmaceutical Association
• Subjects: Analysis; Biological and medical sciences; conformation; cyclosporine; Cyclosporine - chemistry; FTIR; General pharmacology; Immunomodulators; liquid crystal; Medical sciences; Molecular Structure; Pharmaceutical Solutions; Pharmacology. Drug treatments; Protein Conformation; Solvents; Spectroscopy, Fourier Transform Infrared; cyclosporine; conformation; liquid crystal; FTIR; Fourier transformation; Spray drying; Liquid crystals; Powder; Organic solution; Infrared spectrometry; Recrystallization; Ciclosporin; Immunosuppressive agent; Structural analysis; Conformation
• ISSN: 0022-3549; 1520-6017
• DOI: 10.1002/jps.10445

The conformational state of cyclosporine in liquid crystalline spray-dried powders and the solution structure of cyclosporine, in a series of organic solvents where solvent dipole and hydrogen bonding ability varied, were determined. Fourier transformed infrared spectra (FTIR) were obtained on cyclosporine powders, and cyclosporine solutions in a series of organic solvents. Tetragonal crystalline cyclosporine revealed an intermolecular aggregate band at 1614cm−1, a β-sheet band at 1627cm−1, a γ-loop band at 1648cm−1, a γ-turn band at 1658cm−1 (formed from a hydrogen bond between D-Ala8NH and MeLeu6C═O) and a Type II β-turn band at 1673cm−1 (centered at the hydrogen bond betweenVal5NH to Abu2C═O). A similar conformation was observed in chloroform or octanol (apolar), where a second β-sheet band emerged at 1638cm−1 and a turn structure associated with the β-OH on MeBmt1 appeared at 1685cm−1. However, the spray dried liquid crystal structure resembled the solution conformation in acetone or acetonitrile (hydrogen bond acceptor). The conformation in acetone suggested that the β-sheet, γ-loop, Type II β-turn and MeBmt1 turn remained intact. Interestingly, the spray-dried powder conformations did not resemble the solution structure of the solvent (ethanol) from which they had been obtained. The conformation in ethanol and methanol (hydrogen bond donor) showed only β-sheet, γ-turn, MeBmt1 turn structure. Only a small population of molecules retained the Type II β-turn. Finally, cyclosporine is essentially insoluble in water, so the water conformation has never been elucidated; however, a conformation resembling the active structure was obtained in a cosolvent solution containing both hydrogen bond donors and acceptors. This conformation is in good agreement with molecular modelling studies where cyclosporine is docked in the active site of cyclophilin. Spray-dried cyclosporine formed a liquid crystal that can be described as maintaining the Type II β-turn, β-sheet, and γ-loop structures seen in crystalline material. However, the hydrogen bond between D-Ala8NH and MeLeu6C═O was disrupted. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association.