On the synthesis, isolation, and radiochemical studies for the preparationof in-house kits for Tc-99m-meso- and d,l-HMPAO: A few additional observations

The simple procedure documented for the synthesis of d,l-hexamethyl propyle ne amineoxime (d,l-HMPAO), the widely used radiopharmaceutical precursor fo r cerebral perfusion studies, has provided no clue to the inherent difficul ties associated with the isolation of this desired isomer in moderate yield s from the diastereomeric mixture. In addition, determination of the diaste reomeric purity of the isolated fractions with the help of suitable analyti cal techniques has posed a major challenge. Herein, we report the protocol standardized for the purification and isolation of d,l-HMPAO in significant ly improved yields from the crude diastereomeric mixture by fractional crys tallization using a dual solvent system. In addition to the use of high res olution H-1-NMR, C-13-NMR as a suitable analytical tool for conclusive dete rmination of the diastereomeric composition of HMPAO is being reported for the first time. Intermediate stages of crystallisation in the process of pu rification yielded a third product resulting in reduction of the yield of t he desired product. Attempts made to characterize this product are discusse d. Labelling of d,l-HMPAO with Tc-99m was standardized in our laboratory us ing stannous tartrate as the reducing agent The radiochemical studies of th e meso isomer, which is also isolated in the process of crystallization in adequate amounts, have been standardized with a view to investigating its p otential use for leukocyte labelling studies. The biodistribution studies o f the Tc-99m complexes prepared from the pure meso and d,l isomer in Swiss mice are reported. Diastereomeric forms of HMPAO were isolated in increased yields using an improved protocol by fractional crystallization involving a dual solvent system. High resolution C-13-NMR spectroscopy has been utili zed to provide a conclusive analytical tool for efficient and simple screen ing of the diastereomeric composition. An additional compound exhibiting a different crystal habit and spectroscopic features was isolated in the proc ess of crystallization. Tc-99m complexes of both the diastereomers were sta ndardized and used in animal biodistribution studies.