Adduct linkage

Our studies have revealed that the structures of aromatic amine-DNA adducts are determined primarily by their size and coplanarity, as well as the nature of the adduct linkage (C8, N2, etc). It has been shown that aromatic amine lesions exist primarily in three well-defined conformational categories (S, B, W) and their population balance is strongly influenced by the sequences surrounding the lesion site. It is believed that the S/B/W ratios of aromatic amine adducts, not the subtle structural differences at the lesion site (e.g., rotamers, C8 versus N2 linkage, etc), determine the nature of the conformation-specific repair and mutational outcomes. As such, the available data points towards a new paradigm lesion bypass (either error-free or error-prone) depends on various factors, including the thermodynamic and conformational characteristics of the lesion at the replication fork,... 

The XeF+ cation forms Lewis acid—base adduct cations containing N—Xe—F linkages with nitrogen bases that are resistant to oxidation by the strongly oxidizing XeF+ cation having an estimated electron affinity of the XeF+ cation of 10.9 eV (12). The thermally unstable colorless salt,... 

The enzyme catalyzes the hydrolysis of an amide bond linkage with water via a covalent enzyme-inhibitor adduct. Benzoxazinones such as 2-ethoxy-4H-3,l-benzoxazin-4-one [41470-88-6] (23) have been shown to completely inactivate the enzyme in a competitive and stoichiometric fashion (Eigure 5). The intermediate (25) is relatively stable compared to the enzyme-substrate adduct due to the electron-donating properties of the ortho substituents. The complex (25) has a half-life of reactivation of 11 hours. 

Adducts In the context of toxicology prodncts of stable linkages between xenobiot-ics and endogenons molecnles (e.g., between PAH metabolites and DNA). 

Diyne 66, which possesses a three carbon linkage between the alkynes, also reacts with aldehyde 67 in presence of [Ni(COD)J/SIPr catalytic system (Scheme 5.19). However, the connectivity of the dienone 69 obtained from this diyne was different from those obtained from diyne 60. In the former case, adduct 69 was obtained from a )5-hydride elimination of the nickelacycle 68 instead of a reductive elimination. 

Much work has been devoted to the study of Schiff base complexes, in particular M(salen), where M = metal, has been the subject of extensive work 114). The early work by Calvin et al. (section 111(A)) suggested that the 2 1 (M O2) dioxygen adduct, type I, formed by Co(salen) in the solid state, contains a peroxo linkage. An X-ray analysis 115, 116) of the complex (Co Salen)202(DMF)2 supports this hypothesis see Fig. 5 for the pertinent results of this study. 

The nucleophiles participating in reaction with QM3 are typically obvious from the QM linkage identified in the products of all deoxynucleosides except for dA. Direct reaction to form the observed adduct at the exo 6-amino group of dA was still considered surprising due to its weak nucleophilicity, and an alternate pathway involving initial reaction at the most nucleophilic dA N1 followed by a Dimroth rearrangement that interconverts the N1 to the 6-amino groups seemed more reasonable... 

The key structural features of compound 1 are the chiral cis-diaryl benzox-athiin fused ring system, two phenols, and one phenol ether linkage with the pyrrolidinylethanol. Originally, SERM 1 was prepared by medicinal chemists from a key ketone intermediate 5 shown in Scheme 5.1. Compound 5 was prepared in four steps with rather low yield [4a], Among these steps, the high temperature de-methylation step and the use of extremely toxic MOM-C1 were not particularly suitable for scale-up. The ketone 5 was then brominated with PhMe3NBr3 (PTAB) and coupled with thiophenol 7 to produce adduct 8. The key step of the synthesis was the conversion of adduct 8 to cis-diaryl benzoxathiin 9 under the Kursanov-Parne reaction conditions (TFA/Et3SiH). This novel reaction allowed the formation... 

Transition metals have been linked to cyclo- and polyphosphazenes by four different methods. First, and most obvious, the linkage makes use of the coordinating power of the backbone nitrogen atoms. The platinum dichloride adduct (referred to earlier) falls into this category. 

Polymers derived from the preceding type of reaction with nitriles,5 amines,6 and phosphines,7 have been reported. Green8 has reported the preparation of a resin-type material composed of at least 10 repeat units from the reaction between decaborane and adiponitrile (NC(CH2)4CN). Also reported,9 is the inclusion of flexible siloxanes and ether linkages into a diamine, and of their subsequent reaction with decaborane to give adduct polymers (see 2, 3). 

In general these reactions are base-catalysed in that it is necessary to remove a proton from HCXYZ in order to generate the carbanion, eCXYZ, the effective nucleophile one or more of X, Y and Z are usually electron-withdrawing in order to stabilise it. The initial adduct (84) acquires a proton from the solvent (often H20 or ROH) to yield the simple addition product (85). Whether or not this undergoes subsequent dehydration (86) depends on the availability of an H atom, either on an a-carbon or where X, Y or Z = H, and also on whether the C=C so introduced would, or would not, be conjugated with other C=C or C=0 linkages in the product ... 

Whereas the alcohol and phenol derivatives are characterised by ether linkages, adducts of ethylene oxide with fatty acids give rise to both monoesters (9.45) and diesters. These are... 

The formation of hydrogen chloride in the reaction medium can lead to products of its addition to the olefinic linkage.156 Yields of such adducts are increased by the use of solvents of low polarity that are weak electron acceptors, such as dichlorodimethylsilane (Equation 4.34).157... 

The synthesis of (3-D-fructofuranosides is yet another useful application of this concept [293-295]. The latter 1,2-cis-glycosidic linkage is as difficult to establish as in the case of (3-mannosides. In an elegant synthesis of a-D-fucofuranose-containing disaccharides, Plusquellec and coworkers used the IAD concept via p-methoxybenzylidene acetals in combination with a glycosylation protocol via pentenyl glycosides. Here, the intermediate NIS-adduct could be isolated (Scheme 5.108) [295]. 

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