4"-amino-substituted second-generation

On the basis of both structural correlation between benzotriazine and Qx nucleus and mode of action reported for QDO, Monge et al. described at a first time 3-amino-2-cyano-substituted QDO as selective hypoxic cy-totoxins, bioreductive compounds, i.e., compounds 38-41 (Table 6) [27]. In this first approach, the best compounds were the 7-electron-withdrawing substituted derivatives. Electrochemical properties, assessed via voltammet-ric studies, showed that as the electron-withdrawing nature of the 6-(7)-substituent increases, the reduction potential becomes more positive. Compounds with reduction potential more positive are more hypoxia-cytotoxic. However, due to the poor solubility in water of these derivatives, a new generation of compounds was designed and synthesized, i.e., compounds 42-45 (Table 6) [28]. In this second generation of compounds it is possible to highlight derivatives 42 and 45 (Table 6) with excellent hypoxic potency... 

An example of a second-generation biopharmaceutical obtained by site-directed mutagenesis is TNKase (Tenecteplase ), which is an altered form of recombinant tPA produced in CHO cells by Genentech. The substitution of three amino acids in the native protein results in a molecule with higher affinity for its receptor (fibrin), a higher resistance to its natural inhibitor (PAI-1), and an increased half-life (Walsh, 2004). 

Darbepoetin alfa is a second-generation ESA. It is a 165-amino-acid protein, with five N-linked oligosaccharide chains resulting from five amino acid substitutions in the erythropoietin peptide backbone. As a result of this, it has a longer half-life than erythropoietin, and so is given either once a week or in some patients, every two weeks. In addition, due to its longer duration of action, the intravenous and subcutaneous doses of darbepoetin alfa are the same. 

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