Dinucleotide chelates

The stoichiometric reactions of nine oxy and deoxy guanine and/or cytosine containing dinucleotides with cis - [Pt(NH3>2(H20)2] (N03>2 00-5 - 5 X lO- M) in water give monomeric platinum dinucleotide chelates in every case. The complexes have been isolated by HPLC and characterized by NMR and CD analyses. GpG, d - GpG and d - pGpG give a single N7 - N7 anti-anti complex. CpC and d-pCpC... 

A very interesting observation, first made by Chottard et al.70), deals with the occurrence of conformational isomers after chelation of cisplatin to a number of dinucleotides. In certain cases these isomers are rapidly interconverted, but in many cases they are easily separated by chromatographic techniques, and allow characterisation by NMR techniques70,72 75,92 For such an analysis, application of high-field NMR in conforma-... 

Mikalsen A, Capellmann M, Alexander J. 1995. The role of iron chelators and oxygen in the reduced nicotinamide adenine dinucleotide phosphate-cytochrome P450 oxidoreductase-dependent chromium(VI) reduction. Analyst 120 935-938. 

Three human redox enzymes, and a variety of bacterial enzymes, contain molybdenum chelated by two sulfur atoms in a modified pterin molybdopterin (see Figure 10.1). In sulfite oxidase, the other two chelation sites of the molybdenum are occupied by oxygen in xanthine oxidase / dehydrogenase (Section 7.3.7) and aldehyde oxidase, one site is occupied by oxygen and one by sulfur. In some bacterial enzymes, molybdopterin occurs as a guanine dinucleotide rather than free. In others, tungsten rather than molybdopterin is the chelated metal there is no evidence that any mammalian enzymes contain tungsten. 

The evolutionarily conserved Moco biosynthetic pathway consists of three steps (Scheme 1) (1) the conversion of a guanosine derivative (probably guanosine triphosphate) into sulfur-free Precursor Z via insertion of C-8 between the ribose C-2 and C-3 atoms, (2) sulfurization and transformation of Precursor Z into MPT, catalyzed by MPT-synthase, and (3) metal incorporation through chelation of the dithiolene moiety. Additional steps are involved in the attachment of a nucleotide to generate the dinucleotide forms found... 

For all the dinucleotides studied, independently of the nature of the bases, platinum chelation induces an N-type conformation for the 5 - sugar, while the 3 -sugar adopts a predominantly S-type conformation (42, 32). A more detailed analysis of the sugar conformations is undertaken. 

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