Vibrational spectroscopic studies of solid recombinant bovine growth hormone and related growth hormone analogs.

Infrared and Raman spectra have been obtained for lyophilized recombinant bovine growth hormone (r-bGH), partially reduced, and completely reduced r-bGH, plus a tryptic digest fragment of r-bGH. Amide I and II data indicate r-bGH to have substantial helical character. Partially reduced r-bGH, in which the carboxyl terminal disulfide bridge (residues 181, 189) has been cleaved, has slightly less helical content than r-bGH. The spectral data indicate that breaking the carboxyl terminal cystine link produces only localized structural alterations. The additional cleavage of the second disulfide bridge (residues 53,164) leads to a further decrease in helix content, accompanied by increases in beta-sheet and disordered structures. A tryptic digest r-bGH fragment (residues 96-133), which contains a small amount of biological activity (approximately 10%), has predominantly helical structure.

Tablet dissolution affected by a moisture mediated solid-state interaction between drug and disintegrant.

PURPOSE: To investigate the cause for decrease in delavirdine mesylate 200 mg tablet dissolution upon exposure to high humidity. METHODS: Dissolution testing was performed using the USP 2 (paddle) apparatus. Water in tablets was measured by Karl Fischer titration. 13C CP/MAS NMR was used to identify and quantify delavirdine form changes in tablets. FT-IR spectroscopy was used to monitor delavirdine form change in tablets and component mixes, and to investigate a solid state reaction with the disintegrant. RESULTS: Dissolution extent of delavirdine mesylate 200 mg tablets was substantially decreased after exposure to high humidity. This effect is related to the amount of water present in the tablet matrix. 13C CP/ MAS NMR detected about 30% conversion from the mesylate salt of delavirdine to its free base form in the tablet matrix. FT-IR spectroscopy demonstrated that a solid state reaction occurs between the freed methanesulfonic acid and the carboxyl sites on the croscarmellose sodium disintegrant. CONCLUSIONS: Water is thought to act as both a reaction medium and a plasticizer for croscarmellose sodium, facilitating protonation of the carboxyl sites on the disintegrant. This reaction has the potential to occur for any acid salt of a free base. The limiting solubility of delavirdine free base formed in the tablets accounts for much of the decrease in the extent of dissolution. A change in inter-particle bonding can explain the reduction in tablet deaggregation during dissolution.

Characterization and interconversion of polymorphs of premafloxacin, a new quinolone antibiotic.

The quinolone antibiotic premafloxacin crystallizes in at least five solid modifications, including three anhydrous phases (Forms I-III), a hydrate, and a methanolate. The anhydrous phases were studied by optical microscopy, X-ray powder diffraction, HPLC, hot-stage microscopy, dynamic moisture sorption gravimetry, differential scanning calorimetry, thermal gravimetry, and solution and isothermal calorimetry. Dry samples of Form I converted to Form II and ultimately to Form III through a sequence of melts and recrystallizations. Form III was stable to its melting temperature near 200 degrees C. Humidified samples of Form I converted directly to Form III via a moisture-mediated solid-state phase transformation at temperatures as low as 40 degrees C. The calorimetric and solubility data confirmed that Form III was lower in free energy and enthalpy than Form I at room temperature. Our investigation revealed that Form I was not crystallized directly from solution. Rather, Form I was the product of facile solid-state desolvation of the methanol solvate.

Solid phases of delavirdine mesylate.

Delavirdine mesylate was recrystallized from solution under a variety of conditions. Seven crystal forms and a stable amorphous phase were isolated from solution. Two of these crystal forms were polymorphic anhydrates: from XI (U-90152T) and form VIII (U-90152S). Two hydrates (forms VI and XIV), an ethanol solvate (form VII), an acetonitrile solvate (form XIII), and a solvate from methanol/acetone (from XII) were also identified. Six additional phases were identified as the products of solid-state transformations of the hydrated and solvated phases. The solid phases were differentiated by infrared spectroscopy and X-ray powder diffraction. Several of the solid-state phase transformations were mediated by atmospheric moisture. These transformations were studied as a function of relative humidity with dynamic moisture sorption gravimetry (DMSG). DMSG also provided useful measurements of hygroscopicity.

Investigations of protein structure with optical spectroscopy: bovine growth hormone.

Optical spectroscopy provides a wealth of information about protein structure that is difficult to obtain from other methods. Investigations of changes in primary, secondary, tertiary, and quaternary structure are particularly well-suited for optical techniques such as UV absorption, circular dichroism, fluorescence, Raman and infrared spectroscopy, as well as light scattering methods. Each method has unique areas of applicability and contributes to structure determination in a different manner. The application of these methods is demonstrated with examples of studies performed on bovine growth hormone. Some of these include: determination of solution-state structure, monitoring differences between solution- and solid-state structure, determination of molecular size distribution, and investigations of protein folding mechanisms. It is demonstrated that by judicious choice of methods, a reasonably complete description of protein structure can be obtained.

Polymorphism of 1,2-dihydro-6-neopentyl-2-oxonicotinic acid: characterization, interconversion, and quantitation.

Two polymorphs of 1,2-dihydro-6-neopentyl-2-oxonicotinic acid have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermal (hot-stage) microscopy (HSM). In batch-scale preparation, form I was crystallized in ethanol-water (3:1), while form II was obtained by recrystallization from acetone-water (2:1). The melting points for forms I and II are 193 and 196 degrees C, respectively. Thermal studies (DSC and HSM) showed that form II melts at 196 degrees C, while form I melts at 193 degrees C, immediately followed by a resolidification and remelt at 196 degrees C. The conversion of form II to form I was accomplished by recrystallization from ethanol or methanol, and the form I-to-form II transition was obtained by controlled heating of form I around 194 degrees C. Quantitative XRD was used to determine the polymorphic composition, with a detection limit of less than 1% of the minor form and a linearity of 0-10% form I in form II (correlation coefficient of 0.999).