The Chemistry of Nitroimidazole Hypoxic Cell Radiosensitizers

Abstract

It is now well recognised that the imidazole ring system is an important component of many different types of natural products having a wide range of biological activities, including those essential for life itself. For example, in the form of the amino-acid L-histidine it is present in a variety of peptides, proteins and related macro-molecules and it fulfills an important functional role at the active sites of many different enzymes. The imidazole-1-β-riboside moiety, present in the purine nucleotides derived from adenine and guanine, forms an essential chiral building block in the macromolecular structure of the nucleic acids whilst other phosphate esters of the corresponding nucleosides, such as ATP, ADP and cyclic-AMP derived from adenosine, have vital functional roles in all living cells. The imidazole ring system is also found in various forms among low molecular weight natural products of animal, plant and microbial origin; either in simple form, as in the bio-amine histamine, or in much modified form, as in the vitamin biotin. One of the simplest of biologically active imidazoles is the antibiotic azomycin (I), first isolated in 1953 by the group of Umezawa1 and identified in 1955 by Nakamura2 as the hitherto unknown 2-nitroimidazole (Fig. 1).