Posted by 2-Hydroxypropyl-β-cyclodextrin (HPBCD) is one of the most important cyclodextrin derivatives, finding extensive applications in the pharmaceutical sector. Beyond its role as an excipient, HPBCD achieved orphan drug status in 2015 for Niemann-Pick type C disease treatment, prompting research into its therapeutic potential for various disorders. However, the acceptance of HPBCD as an active pharmaceutical ingredient may be impeded by its complex nature. Indeed, HPBCD is not a single entity with a well-defined structure, instead, it is a complex mixture of isomers varying in substituent positions and the degree of hydroxypropylation, posing several challenges for unambiguous characterization. Pharmacopoeias’ methods only address the average hydroxypropylation extent, lacking a rapid approach to characterize the substituent positions on the CD scaffold.
In a recently published study [1], a simple NMR spectroscopy-based approach has been described to analyze the distribution of the hydroxypropyl sidechains (i.e. the pattern of substitution). The characteristic chemical shifts of the hydroxypropyl sidechains in different position of substitution have been differentiated for the first time as a basis for the evaluation. This precise identification enabled accurate assignment to the respective positions, enhancing the capability for a more thorough structural characterization of this industrially significant cyclodextrin. With just one series of experiments, utilizing easily accessible instrumentation, not only the DS can be determined but also the pattern of substitution can be delineated. For example, CAVASOL® W7 HP was found to have 58 % substitution at C2, 32 % at C3 and 10 % at C6 position. Such a comprehensive structural information obtained in a fast, non-destructive and robust way has the potential not only to assist studies on structure-activity relationship of HPBCD but also, in the future, to serve as an efficient tool for regulatory purposes in controlling the uniformity and the quality of this up-and-coming CD and promising API.
[1] Kalydi, E., Malanga, M., Nielsen, T. T., Wimmer, R., & Béni, S. (2024). Solving the puzzle of 2-hydroxypropyl β-cyclodextrin: Detailed assignment of the substituent distribution by NMR spectroscopy. Carbohydrate Polymers, 122167. https://doi.org/10.1016/j.carbpol.2024.122167