Polyamine linkers

A variety of polyamine linkers were developed by Bradley and colleagues [152,162,163]. They mainly use an aminomethylated polystyrene resin 111 (Table 1). An urethane linkage was found to be cleavable using strong acidic conditions (lOequiv trifiuoromethanesulfonic acid-trifluoroacetic acid, TFMSA/TFA) and hence is potentially useful for resin screening purposes. Other linkers such as the trityl linkers (114, 116-120) (Table 1) are readily cleavable with TFA and are ideal for solution screening applications. 

Endonuclease-catalyzed hydrolysis of DNA at the internucleosomal linker regions into multimers of 180 base pairs which are visualized by electrophoresis as a ladder of nuclear DNA fragments. Access of the endonuclease to DNA is facilitated by depletion of polyamines, and the activity of the enzyme is mcrea.sed by and decreased by ADP-tibosylation. Thus, agents that increase intracellular Ca " or inhibit l>oly(ADP-ribose) polymerase can induce apoptosi.s. ... 

Lehn synthesised guanidinium-based cationic steroids incorporating an acylhy-drazone linker using the approach shown in Fig. 9 [141]. The synthesis was developed from a polyamine scaffold by guanidination of the primary amino groups and alkylation of the secondary amine with methyl chloroacetate to introduce the ester moiety required to form a hydrazide group by reaction with hydrazine monohydrate. Cationic steroid hydrazones were then prepared via an acetic acid catalysed reaction with cholestanones, which demonstrated high transfection efficiency and low toxicity in a variety of cell lines [141]. 

Another interesting modification of glass surfaces was introduced by Beier and Hoheisel.23 They synthesized a flexible, dendritic linker system that enables covalent immobilization of oligonucleotides and PNAs with high loading capacity in a controlled manner. This method facilitates the modulation of surface properties such as hydrophobicity and charge. The synthesis of the linker system involves two consecutive reactions an acylation of surface-bound amine groups with acid chloride (4-nitrophenyl-chloroformate or acryloylchloride) and subsequent reaction with an amine. A bis-amine results in a linker system, while a polyamine produces a dendritic structure (Fig. 14.3). Because polyamines possess primary and secondary amine... 

Dinuclear complexes formed with polyamines have attracted attention since polyamines are known to interact with the DNA backbone. Dinuclear cationic trans complexes that use the natmally available polyamines spermine (19) and spermidine (20) as linkers have been shown to be very active and to circumvent cisplatin resistance in L1210 mmine leukemia cells in vitro. The internal charge, from an incorporated amine (19) and (20) or a platinum atom (18), featmed in the diamine linker, seems to contribute significantly to the anticancer activity of the complexes. 

Primary and secondary di- and polyamines are used as chain extenders and cross-linkers. Aromatic amines are more reactive than aliphatic ones. 

Recently, a modified trityl linker for amines (36) (Fig. 4) has been introduced, and was used for the synthesis of polyamine derivatives [40]. 

Polyamines as strong covalent linkers for the assembly of mono and double layers of zeolite crystals on glass... 

In the thesis of polyethylenimine-coated supports there is variability introduced by the polyamine as well as the cbrace of ooss-linker employed. For instance, cross-linking is prevalent during the polymerization of ethy-lenimine and there is normally a distribution of 25% primary amines, 50% secondary amines, and 25% tertiary amines (.101). Berause of the chemical variability in these stationary phases several methods, such as the use of test solutes of varying hydrophobidty and static adsorption isotherms, have been employed in the duuacterization of these phases (37-40,102). 

Two series of bimetallomesogens have been realized with various polyamine units used as a linker between different salylcylaldimine moieties. The first system was reported by Berdague et al. who complexed dicarbonyl-rhodium(I) and -iridium(I) to a dimeric salicylaldimine bridged by a 1,4-diaminocyclohexyl unit ((226) M = Rh, Ir). Both complexes showed an SmA phase, that of the iridium (Cr 142 SmA 169 I) compound having a higher mesophase stability than the rhodium congener (Cr 141 SmA 145 I). 

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