Application of NIR spectroscopy in polymorphic analysis: study of pseudo-polymorphs stability.

The accelerated transformation of three azithromycin pseudo-polymorphs (viz. the anhydrous, monohydrate (MH), and dihydrate (DH) forms) at a high temperature and moisture level was examined by near infrared spectroscopy (NIRS). The most marked spectral differences between the pseudo-polymorphs occurred in the 1800-2200 nm region, which corresponds to the first overtone for water. The qualitative analysis of the NIR spectra for the pseudo-polymorphs following storage in a stove at 60 degrees C at 100% relative humidity for 60 days suggests that the crystalline forms (viz. the MH and DH) are stable, whereas the amorphous (anhydrous) form evolves to the DH. This was confirmed by determining the amounts of water and DH present in anhydrous azithromycin and the MH by use of partial least-squares regression (PLSR). The method used to quantify the DH in MH samples was developed and validated in accordance with the standards of the International Conference of Harmonization (ICH) and the European Medicines Agency (EMEA) with a view to its subsequent application by the pharmaceutical industry. The limits of detection (LD) and quantitation (LQ) for the DH in MH provided by the NIRS method were consistent with those obtained by X-ray diffraction (XRD) methodology. This testifies to the accuracy of the proposed method.

A Novel Domino Reaction: Cyclization of Alkynyl Sulfides by Reaction with IPy2 BF4.

Formation of polycyclic structures within a few minutes: The intramolecular cyclization of diynes, activated by a benzenesulfenyl substituent, upon reaction with IPy2 BF4 proceeds as an efficient exo-endo coupling. A subsequent novel Friedel-Crafts-like ring closure provides the product [Eq. (1)]. Thus, intra- and intermolecular cyclizations can be carried out.

Versatile Synthesis of Dihydroquinolines and Quinoline Quinones Using Cyclobutenediones. Construction of the Pyridoacridine Ring System.

1-BOC-2-lithio-1,4-dihydropyridines were condensed with 3,4-disubstituted cyclobutenediones to produce 1,2-adducts. Neat thermolysis under oxygen-free conditions produced substituted 1,4-dihydroquinoline hydroquinones in which the tert-butoxy residue of the BOC group was displaced by a phenolic residue, generating an oxazolone ring that functioned to protect both rings of the dihydroquinoline hydroquinone from untimely oxidation. Oxidative aromatization with concomitant loss of the oxazolone ring was achieved using 2 equiv of o-chloranil in acetic acid and provided substituted quinoline quinones in good yields. By use of this strategy, a concise synthesis of the pyridoacridine ring system was achieved.