Microscopic molecular mobility of amorphous AG-041R measured by solid-state 13C NMR.

PURPOSE: AG-041R is characterized to be stable in amorphous state and difficult to crystallize at normal period of time. In order to investigate the molecular mobility in microscopically, the spin-lattice relaxation time (T1) of AG-041R was investigated by solid-state CP/MAS 13C NMR at temperature below and above glass transition temperature (Tg). METHOD: CP/MAS measurement and T1 measurement were performed by means of 13C NMR, where the measurement temperatures were 60, 70, 80, 100, and 110 degrees C. The spin-lattice relaxation time (T1) of AG-041R was calculated from the relaxation curves. RESULTS: From the analysis of T1 of amorphous AG-041R, it was clarified that all of the carbons did not start moving drastically at Tg and there were some groups of carbon in terms of temperature dependency of T1. One is a type, such as the carbons in benzene ring: their T1 was drastically changed at Tg. On the other hand, T1 of carbonyl carbons gradually decreased, and above Tg their T1 was still higher than that of the other carbons. There was no significant change of T1 in the methyl carbons around Tg. From the study of IR and 1H NMR in solution, the inter- and intramolecular hydrogen bondings between NH and C=O were found in AG-041R. Due to hydrogen bonding, the inter- and/or intramolecular interaction is considered to retain even at supercooled liquid state. CONCLUSION: The structure that contributes glass transition is the main skeleton structure, such as benzene ring, while small group, like methyl, start to move at lower temperature than Tg. On the other hand, for the carbons, such as carbonyl, their structure was restricted by inter- and/or intramolecular interaction, therefore, their molecular mobility was significantly low above Tg.

A study of the substrate specificity of Na+-dependent and Na+-independent neutral amino acid transport systems in dog intestinal brush-border membrane vesicles using L-alanine analogues.

Neutral amino acids are mainly transported across the intestinal brush-border membrane by two Na+-dependent systems (system B0 and system B0+) and one Na+-independent system (system b0,+). To investigate potential differences in substrate specificity between these systems, we screened ten different alanine analogues for their ability to inhibit the transport of L-alanine in dog intestinal brush-border membrane vesicles. The results suggested that a phenyl group directly attached to the alpha-carbon has different effects on the Na+-dependent and Na+-independent transport systems, with an increased affinity for the former and a decreased affinity for the latter. Based on these inhibition studies, we investigated [14C]L-phenylglycine transport kinetics in comparison with L-alanine. Similar to L-alanine, L-phenylglycine transport followed at least three routes, however, the Km of the Na+-dependent transport system was lower and the K'm of the Na+-independent system was higher than the corresponding values for L-alanine. These results corroborated the conclusions drawn from the inhibition studies. Based on these data, we conclude that different sizes of immediate parts to the alpha-carbon in functional groups of amino acid analogues have differential effects on the interaction of these amino acid analogues with the Na+-dependent and Na+-independent transport systems for neutral amino acids.

Characterization and monitoring of pseudo-polymorphs in manufacturing process by NIR.

Moisture-sensitive pseudo-polymorphs with different stabilities were characterized, and their polymorphisms were monitored in the process of tableting and film coating by near-infrared (NIR) spectroscopy. In this study, we proved that we could successfully maintain the crystal form ratio in the tablet by controlling the moisture profile during the manufacture to sufficiently stabilize the drug product. Mitemcinal fumarate is an erythromycin derivative with two pseudo-polymorphic forms, hydrate and anhydrate. We characterized them by X-ray powder diffraction and water sorption isotherm plot analysis. Stability test revealed that the hydrate form is more stable than the anhydrate form. We established a quantitative method by using NIR and monitored the hydrate form ratio in the tablet during the tableting and coating process. The manufacturing room was controlled to between 40 and 60% RH. Although the hydrate form ratio just after the onset of tableting decreased to below 40%, 60% was obtained at the end of the final process which sufficiently retains stability. Transition of the hydrate form ratio during the manufacturing process was reasonable; this indicates that our NIR method is suitable for monitoring. Thus, NIR is one of the most suitable tools for in-process testing of these humidity-sensitive APIs.