Distinguishing between polymorphic forms of linezolid by solid-phase electronic and vibrational circular dichroism

Area of Science:

• Solid-state spectroscopy
• Chiroptical methods
• Pharmaceutical analysis

Background:

• Linezolid is a crucial antibiotic, and understanding its crystalline forms (polymorphs) is vital for drug formulation and efficacy.
• Polymorphism can significantly impact a drug's physical and chemical properties, including solubility and bioavailability.
• Solid-state chiroptical spectroscopy offers a powerful, non-destructive method for characterizing chiral molecules in their solid forms.

Purpose of the Study:

• To investigate and differentiate between two crystalline forms (polymorphs) of linezolid using solid-phase electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy.
• To establish spectral markers for distinguishing linezolid polymorph II from polymorph III.
• To demonstrate the utility of solid-phase ECD and VCD in characterizing pharmaceutical polymorphs.

Main Methods:

• Acquisition and analysis of solid-phase ECD spectra of linezolid polymorphs.
• Acquisition and analysis of solid-phase VCD spectra of linezolid polymorphs.
• Comparison of spectral features between different linezolid crystalline forms.

Main Results:

• Distinct differences were observed in the ECD spectra between linezolid polymorph II and polymorph III.
• A specific band at 221 nm in the ECD spectrum was identified as diagnostic, present in form II but absent in form III.
• Significant differences were noted in the VCD spectra, particularly in the carbonyl absorption region, showing two strong bands with opposite signs.

Conclusions:

• Solid-phase ECD and VCD spectroscopy are effective methods for distinguishing between linezolid polymorphs.
• The identified spectral features, especially the 221 nm ECD band, provide reliable markers for polymorph identification.
• This spectroscopic approach contributes to the quality control and characterization of pharmaceutical solid forms.