Acetamidate bridging

An acetamidate-bridged Pt111 complex was proposed before any Pt111 dimer had been discovered [55][56]. The yellow compound, obtained from... 

The reaction rate was found to obey the rate law defined by kobs = kx + k2/[H+] [54]. The acetamidate-bridged [Pt225]8 octamer [Pt8(NH3)16(acet-amidato)8]10+ was also reported to exhibit similar behavior after dissolution in aqueous media (Eqn. 2) [55]. 

Recently, a stepwise synthesis of acetamidate-bridged oligonucleotides has been published by Nyilas et al. (26). They used the 5 -azido-compounds as 5 -aminonucleoside synthons (Fig. 13). 3 -0-carboxymethylation is carried out with sodium chloroacetate in the presence of NaH at 20°C. 5 -Azido-5 -deoxythymidine does not need to be protected, for the other bases, the monomethoxytrityl protection... 

Fig, 11. Unsuccessful attempts to prepare acetamidate bridged polythymidine... 

The acetamidate bridge is stable over a large pH range no hydrolysis is found at pH 6-7.5 at 20 C for 7 d. At pH 14 and 37°C, the half-life is 3.4 h (25). However, other properties of these compounds are less advantageous, such as the low solubility in water, the strong tendency to adsorb onto glass and plastic surfaces and, most unfortunately, they do not show any tendency to hybridize with their complementary natural polynucleotides (25). 

Fig. 12. Preparation of acetamidate-bridged oligonucleosides. Polymerization is effected by triphenylphosphine, 2,2 -dipyridyldisulfide in pyridine, 14 h, 54%.

Fig. 13. Stepwise synthesis of acetamidate-bridged oligonucleosides B Thymine, 4-lV-MMTr-cytosine, 2-lV-MMTr-guanine, 6-TV-MMTr-adenine B unprotected bases cat HOBT, A -ethylmorpholine (i) NaH in DMSO at 0°C for 1-3 d (85%) (ii) DCC, HOBT, IV-ethylmorpholine (27) in DMF, O-20°C, 24h (50-70%) (iii) a. PPh3 at 0°C, 24 h, b. methanolic NHj 24 h (85%) (iv) ZnBr2 in nitromethane, 20°C, 24 h, 70%.

Isomers are, of course, possible when the equatorial ligand lacks a plane of symmetry, as in the corrinoids [see (HI)]. All the acetamide side chains project to one side of the corrin ring, which we shall call the upper side, and all the propionamide side chains and the nucleotide side chain to the lower side. Isomers are then theoretically possible whenever the two axial ligands are different, and their existence has been shown experimentally for corrinoids where one axial ligand is CN , Me, or Et and the other is H2O or is absent [for further details see Section 8.2 of ref. (136)]. Salen and BAE also show minor deviations from planarity due to the bending of the two halves (mentioned above in Section II,B,2) and to torsion about the C—C bonds in the ethylene bridge (see references in Table I), but these are not expected to give rise to separable isomers. 

The synthesis of a water-soluble diphenylmethano-bridged fullerene 122 was achieved by hydrolyzing the bis (acetamide) 121 with acetic acid-aqueous hydrochloric acid and then converting it into the bis(succinamide) 122 by treatment with succinic anhydride (Scheme 4.25) [158]. Compound 122 is soluble in water at pH > 7. This is an important requirement for the investigation of the biological activity of fullerenes. Remarkably, 122 is an inhibitor for the HIV enzymes protease (HIV-P) and reverse transcriptase (HIV-RT) [159]. As suggested by molecular modeling. 

Preparation of the complexes CdX2L2 (X = C1, Br, I or SCN L = acetamide) has been reported. IR evidence indicates bridging halide ligands, with L coordination via O and N.353 The crystal structure of dichlorobis(N,N-dimethyIacetamide)zinc shows zinc tetrahedrally... 

The fact that only Pt111 dimers have been isolated for quadruply-bridged sulfate, phosphate, acetate, and acetamidate complexes indicates that the short bite distance of these ligands destabilizes the Pt2 state, which requires a much longer Pt-Pt distance. 

Next, the authors explored the 02 mechanism. In this case, the largest model used (15) involved two methylammonium ions and two formate ions to mimic the Lys-Asp-Lys-Asp tetrad, and an acetamide hydrogen-bonded to a water, which interacts with 02, to mimic a glutamine-water bridge found in the Wu-Pai crystal structure.22... 

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