Chapter 25, Problem 15P

Interpretation Introduction

Interpretation:

The mechanism of cationic intermediate formed by crosslinking of DNA (deoxyribonucleic acid) to mitomysin and the mechanism for the formation of dihydromitosene are to be represented.

Concept introduction:

舧 A nucleoside consists of a nucleobase (also termed as nitrogenous base), and a five-carbon sugar (either ribose or deoxyribose).

舧 A nucleotide consists of a nucleobase (also termed as nitrogenous base), a five-carbon sugar (either ribose or deoxyribose) and one or more phosphate groups.

舧 In a nucleoside, the anomeric carbon is linked through a glycosidic bond to the N9 of a purine or N1 of a pyrimidine.

舧 Examples of nucleosides include cytidine, uridine, adenosine, guanosine and thymidine.

舧 Sugar (ribose/deoxyribose) and nitrogenous bases are linked through N-glycosidic bonds.

舧 These glycosidic bonds are formed by condensation reaction of first carbon of sugar molecule with the nitrogen atom $(\text{N1 of pyrimidines and N9 of purines)}$ of the nitrogenous base.

舧 This particular glycosidic bond is stable in basic solutions, but readily hydrolyzes in the presence of acids.

舧 DNA is the genetic material in human beings and most of the biological systems. The proportion of DNA is constant in all diploid human cells. However, gamete cells are haploid and are composed of half of the amount of DNA present in diploid cells.

舧 DNA exists in the form of a double stranded helix in which complementary bases are present opposite to each other and form base pairs.

舧 In most common form of DNA, that is, B-DNA, $10\text{ base pairs occupy a distance of 34 }\AA$ >.

舧 Mitomysin is an anticancer agent, which forms DNA crosslinks by binding to amino group of Guanine residue. It bears quinone moiety and aziridine ring along with the heterocyclic purine type ring. This quinone moiety undergoes reduction to form quinol, which cleaves its aziridine ring to form bond with guanine residue. Such bonding causes methylation of amino group in guanine. All these reactions are formed from a cationic intermediate, which is stabilized by quinol groups. Moreover, the intermediate can give rise to 1-dihydromitosene.