Substrates, structure-reactivity Subject

Structures of vitamin B6 derivatives and the bonds cleaved or formed by the action of pyridoxal phosphate (a). The reactive part of the coenzyme is shown in red in (a). The bonds shown in red in (d) are the types of bonds in substrates that are subject to cleavage. 

The parent indolo[2,3-fl]carbazole (1) has also been the subject of a study probing its reactivity toward oxidizing agents. One of the substrates involved, namely 85 (prepared from 1 and 2,5-dimethoxytetrahydrofuran in the presence of acid), was subjected to treatment with m-chloroperbenzoic acid, to give the dione 86 as the major product and a sensitive compound assigned the hydroxy structure 87. A cleaner reaction took place when 85 underwent oxidation with tert-butyl hydroperoxide assisted by VO(acac)2, to produce 86 exclusively in 86% yield. Likewise, A,N -dimethylindolo[2,3-fl]carbazole furnished the dione 88 on treatment with this combination of reagents (96J(X 413). 

The number and breadth of reports of synthetic studies relating to phos-phatidylinositols and related structures has increased markedly as the following selection demonstrates. A series of unnatural phosphatidylinositols (41) with C2 to C18 fatty acids replacing the natural C20 fatty acid at the sn-2 position have been prepared and subjected to phosphorylation conditions with phos-phatidylinositol 3-kinase. The results show that phosphorylation can be achieved in molecules carrying small fatty acid side chains Cg shows reactivity comparable to that of the natural substrate. l-D-l-(sn-3-Phosphatidyl)-myo-inositol (42) has been prepared in excellent yield by the direct phosphatidylation of l-D-2,3,4,5,6-penta-0-benzyl-myo-inositol with sn-3-phosphatidic acid and subsequent deprotection (Scheme 6) The method has the advantage of producing products of unequivocal structure and stereochemical purity and being... 

Electrical measurement of the dielectric constant is done through the fabrication of metal—oxide—semiconductor capacitor structures, where the ULK serves as the dielectric of the capacitor. A doped Si wafer is used as the substrate, on which the ULK film is deposited. This ULK film is subjected to CMP, say, or any other process whose impact on ULK characteristics needs to be quantified. An aluminum film is deposited on the backside of the Si wafer to form one of the capacitor contacts. Using a shadow mask, aluminum dots of varying diameters are evaporated onto the surface of the ULK film, to form the other terminal of the capacitor. Each aluminum dot is probed to measure its capacitance (at about 100 kHz). Evaporation through a shadow mask allows for the formation of metal contacts without altering the dielectric further— as would be the case if reactive-ion-etch were used to form the contacts. (It should be noted that more complex process flows can be used to eliminate concerns such as dot-size variation, the effect of probe-tip impact on the dielectric being tested, etc.) The results of electrical measurement of the k-value increase post-CMP of the variety... 

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