Many analytical techniques, such as differential scanning
calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy (IR) and Raman spectroscopy can be used to differentiate
between crystalline polymorphs of the same chemical entity.
While all of these techniques are routinely applied to off-line
analysis of materials, Raman spectroscopy has the advantage
over these other techniques in that Raman technology currently
exists for in situ monitoring of the solid-phase behavior within
a mixed suspension of liquid and solid. In this work, we present
our results from an in situ Raman study, demonstrating the
solvent-mediated polymorphic phase transformation of progesterone. In situ Raman analysis has shown that the appearance
of Form I progesterone is always preceded by the formation of
Form II progesterone. Phase transformation rates were found
to increase monotonically as the temperature increases, which
indicates that the polymorphic system is monotropic. Form I
was found to be thermodynamically more stable than Form II,
while Form II was found to be kinetically favored over Form
I. The results from this study are consistent with Ostwald's law
of stages and lead to an in-depth understanding of the polymorphic transformation process of progesterone. The in situ
monitoring capabilities of Raman spectroscopy have allowed
us to define the processing parameters required to control the
morphology of crystalline progesterone.
The structure, chemistry, and absolute configuration of actinobolin (1), an antibiotic possessing a broad spectrum of biological activity, is described. When the chemical and spectral properties of N-acetylactinobolin (2) led to a partial structure expressed as a series of four fragments, which together accounted for all atoms in the molecule, computer program cmbn was employed to generate all structures consistent with available evidence. All six structures outputted possessed a /3-ketolactone system. Spin decoupling studies on 2, the periodate oxidation of a sodium borohydride reduction product of 2, and formation of an isopropylidene derivative of 2 narrowed the number to two structures. An nmr study of the totally acetylated 5-pyrazolone derived from 2 upon treatment with hydrazine allowed the assignment of expression 2 as the structure of N-acetylactinobolin. The isolation of L-alanyl-L-threonine from the mild permanganate oxidation of actinobolin established the configuration at C-3, C-4, and C-14 as R, R, and S, respectively. The absolute configuration at C-5, C-6, and C-10 could be assigned as R, R, and R, respectively, by a study of the 100-MHz nmr spectra of 2 and its methyl enol ether 5.
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