Cleavability

PHOST is often prepared by polymerization of 4-acetoxystyrene followed by base-catalyzed hydrolysis (Fig. 29). The acetoxystyrene monomer s stabihty and polymerization kinetics allow production of PHOST of higher quaUty than is easily obtained by direct radical polymerization of HOST. The PHOST homopolymer product is then partially or fully derivatized with an acid-cleavable functionaUty to produce the final resist component. 

A molecule which is not itself symmetrical may still be cleavable to identical precursors. Examples of such cases are carpanone (123)34a n j usnic acid. h... 

General Preparations of Esters General Cleavage of Esters Transesterification Enzymatically Cleavable Esters Heptyl, 381... 

This group was designed as an enzymatically cleavable protective group. Cleavage is achieved using an esterase present in mouse plasma or hog liver carboxylate esterase. " ... 

The phosphate ester, prepared either through phosphoramidite or phosphoryl chloride protocols, is cleavable by photolysis (350 nm, benzene, 83-87% yield)." ... 

Intramolecular cycloadditions of substrates with a cleavable tether have also been realized. Thus esters (37a-37d) provided the structurally interesting tricyclic lactones (38-43). It is interesting to note that the cyclododecenyl system (w = 7) proceeded at room temperature whereas all others required refluxing dioxane. In each case, the stereoselectivity with respect to the tether was excellent. As expected, the cyclohexenyl (n=l) and cycloheptenyl (n = 2) gave the syn adducts (38) and (39) almost exclusively. On the other hand, the cyclooctenyl (n = 3) and cyclododecenyl (n = 7) systems favored the anti adducts (41) and (42) instead. The formation of the endocyclic isomer (39, n=l) in the cyclohexenyl case can be explained by the isomerization of the initial adduct (44), which can not cyclize due to ring-strain, to the other 7t-allyl-Pd intermediate (45) which then ring-closes to (39) (Scheme 2.13) [20]. While the yields may not be spectacular, it is still remarkable that these reactions proceeded as well as they did since the substrates do contain another allylic ester moiety which is known to undergo ionization in the presence of the same palladium catalyst. 

Spalt, m. split, rent, fissure, silt, crack, cleft, gap. -ausleuchtung,/. slit illumination, spaltbar, a. cleavable fissionable fissile, scissUe. 

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

In a few cases, azo polymers were synthesized pho-tochemically. Azobenzoin compounds have photo cleavable benzoin groups. Being irradiated with UV light (A = 350 nm) 4,4 -azo-bis(4-cyanopentanoyl)-bis benzoin, ACPB, undergoes a-scission forming two free radicals per initiator molecule (Scheme 24). 

Cathepsin D. The design of inhibitors of the aspartyl protease cathepsin D started from a virtual library of peptide analogs that contained the typical hydroxyethylamine isoster for the cleavable peptide bond. As the availability of starting materials would have generated a library of about 1 billion compounds, virtual screening was applied to reduce this multitude of candidate structures to a reasonable number. The backbone of a peptide... 

Hoechst 33342 [2 -(4-ethoxyphenyl)-5-(4-methyl-l-piperazinyl)-2,5 -bi-IH-benzimidazole Ho342 I], a bisbenzimidazole dye, binds to adenine/thymine-rich regions in the minor groove of DNA. This dye induces apoptosis and inhibits topo 1 activity in vivo. It has been suggested that the destruction of immunoreactive topo I and topo I-DNA complexes or cleavable complexes results in inhibition of topo I activity, a key step in the Hoechst 33342-induced apoptotic process [40]. 

Vladu et al. [51] synthesized a series of 7-X-lO-Y-camptothecins (VII) and evaluated their ability to trap hiunan DNA topo I in cleavable complexes. We used these data to develop Eq. 5 (Table 3) ... 

In addition to specific properties of interest for a particular application of a material, its elasticity, compressive and tensile strength, deformability, hardness, wear-resistance, brittleness and cleavability also determine whether an application is possible. No matter how good the electric, magnetic, chemical or other properties are, a material is of no use if it does not fulfill mechanical requirements. These depend to a large extent on the structure and on the kind of chemical bonding. Mechanical properties usually are anisotropic, i.e. they depend on the direction of the applied force. 

Although the glycosidic bonds of uronic acid residues are usually more resistant to acid hydrolysis than those of neutral polysaccharides,218 these linkages in heparin are more readily cleavable then those between the hexosamine and the uronic acid residues. Disaccharides obtained by exhaustive hydrolysis of heparin with 0.5 MHC1 at 80° contained hexu-... 

Our interest in the past few years has been on biodegradable polymers. We have been evaluating the potential of poly(phosphoesters) as degradable biomaterials (4).We were attracted to this class of polymers because the phosphoester bond in the backbone is cleavable under physiological conditions, the presence of the P-O-C group would facilitate fabrication, and the versatile chemical structure affords a wide... 

Rodebaugh R, Fraser-Reid B, Geysen HM. A new onitrobenzyl photo-cleavable linker for solid phase synthesis. Tetrahedron Lett 1997 38 7653-7656. 

Millington CR, Quarrell R, Lowe G. Aryl hydrazides as linkers for solid phase synthesis which are cleavable under mild oxidative conditions. Tetrahedron Lett 1998 39 7201-7204. 

The CO-transfer reaction onto o-aminophenol or o-phenylenediamine by GDI has been used as a method for converting /Mactam carbanilides, obtained by a 4-component condensation, into the corresponding carboxylic acids without damaging the sensitive fi-lactam moiety. The method has its basis in the production of easily cleavable compounds from o-hydroxy- and o-aminoanilides and CDI [76]... 

In the reactions considered here the N-acyl group functions as a readily cleavable protecting group in facilitating exclusive alkylation at normally unfavored positions in the azole moiety.[1]... 

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