Substituted guanidines: introducing diversity in combinatorial chemistry.

The guanidine moiety is an important motif present in many biologically active compounds. Fully substituted guanidines are of key importance for the development of bioactive molecules. The present paper reports on an efficient procedure for the direct solid-phase conversion of amines to fully substituted guanidines under very mild conditions.

Comparison of the effects of 5- and 6-HOAt on model peptide coupling reactions relative to the cases for the 4- and 7-Isomers.

Synthesis of 5- and 6-HOAt has completed the full set of the four HOAt isomers derived from HOBt by insertion of a single nitrogen atom in the benzenoid nucleus. Comparison of the reactivity of all four isomers in model peptide coupling reactions has confirmed the unique character of the 7-isomer in promoting selectivity and maintaining configuration at the reactive carboxylic acid residue.

Hot melt coating technology: influence of Compritol 888 Ato and granule size on chloroquine release.

The tangential spray technique was used to coat chloroquine granules with Compritol 888 Ato in a fluidized bed (Glatt GPCG-1,1). After validation of the assay method for chloroquine, dissolution tests were carried out on four size fractions obtained from the same batch of granules. The dissolution profiles obtained showed differences in the rate of release between one fraction and another, despite the fact that each of these fractions had been coated with the same quantity of wax. This suggests that the rate of release of the chloroquine may be adjusted by controlling the size of the granules. Furthermore these dissolution profiles were characterized by a rapid release phase followed by a slow release phase. Examination of the surfaces of the granules from the various size fractions under a scanning electron microscope revealed that Compritol did not form a continuous film but existed rather as a lipid environment around the granule. This lipid environment was made up of solidified droplets of the wax which had become piled up on the surface of the granule. Compression of the granules produced tablets which remained intact until chloroquine dissolution was complete. This undicated that the active substance diffused across the Compritol matrix generated during compression. Determination of the dissolution kinetics using the Higuchi model demonstrated the diffusion release mechanism.

Hot-melt coating technology. I. Influence of Compritol 888 Ato and granule size on theophylline release.

The aim of this work was to study the influence of theophylline granule size and the percentage of Compritol 888 Ato on in vitro drug release from granules and tablets. The granules were coated in a fluidized bed apparatus. The dissolution profiles of these granules differed from those of granules coated with classical agents, and there were also differences between the various sieve fractions studied. Drug release was characterized by a rapid-release phase, followed by a slow-release phase. Results indicate that theophylline release can be controlled by controlling granule size. Inspection of the appearance of the tablets at the end of the dissolution test revealed that all tablets containing Compritol 888 Ato remained intact. This indicated that the Compritol 888 Ato used in the tablet formulation created an inert matrix through which the drug diffused. It was found that the Higuchi relationship of linear square root of time was the best model to describe the release kinetics of the drug from tablets. This also confirmed that a matrix diffusion-controlled mechanism was operative. Given the difference between the dissolution profiles of the granules and the tablets, it was concluded that this matrix is formed during compression.