Synthesis and preliminary cytotoxic activity of dimethoxy-acridines and dimethoxynitroacridines

The preparation of a series of dimethoxy and dimethoxynitroacridines and their activity in oxic and hypoxic cells is reported. Anthranilic acids 1,4,14 were prepared according to the Ullmann condensation. 9-chloroacridines were obtained from anthranilic acids by refluxing in phosphorus oxychloride. The synthesis of two new acridine dimers 9,10 is described. Nitration of 9-chloro-2,4-dimethoxyacridine 15 gave 3-nitro isomer 19 . By phenol-mediated coupling reaction from all the 9-chloroacridines, the respective 9-(alkylamino)acridines were obtained. By nitration of 17 a new 2,4-dimethoxy-3,7-dinitroacridine 21 was prepared     

Why isn't 'standard' heme good enough for c-type and d1-type cytochromes?

This perspective seeks to discuss why biology often modifies the fundamental iron-protoporphyrin IX moiety that is the very versatile cofactor of many heme proteins. A very common modification is the attachment of this cofactor via covalent bonds to two (or rarely one) sulfur atoms of cysteine residue side chains. This modification results in c-type cytochromes, which have diverse structures and functions. The covalent bonds are made in different ways depending on the cell type. There is little understanding of the reasons for this complexity in assembly routes but proposals for the rationale behind the covalent modification are presented. In contrast to the widespread c-type cytochromes, the d1 heme is restricted to a single enzyme, the cytochrome cd1 nitrite reductase that catalyses the one-electron reduction of nitrite to nitric oxide. This is an extensively derivatised heme; a comparison is drawn with another type of respiratory nitrite reductase in which the active site is a c-type heme, but the product ammonia.