Fragment protected

S. Choi et al.. Hydrogen peroxide-mediated Cu,Zn-superoxide dismutase fragmentation protection by carnosine, homocamosine and anserine. Biochim. Biophys. Acta, 1472 (1999) 651-657. 

Fig. 3 Appearance of fragments protected from micrococcal nuclease digestion following incubation of Xenopus sperm chromatin in homologous egg extract. Sperm nuclei were used without extract incubation (lane 2) or following incubation of 50 ng DNAZ/il egg LSS for 3 min (lane 3), 10 min (lane 4), 30 rain (lane 5), or 120 min (lane 6). Samples were diluted and the sperm nuclei were isolated by centrifugation. The samples were digested with micrococcal nuclease for 1 min and the DNA purified and separated by a 1.4% Tris-borate-EDTA agarose gel. Lane I shows molecular weight markers in lOO-base-pair increments.

Thomas HL. Needle-punched non-woven fabric for fragmentation protection. PASS 2004. 

In the absence of peptide synthesizing equipment and for special cases where it is either inappropriate (for reasons of economy) or where the mechanical method will not work because the methods that are used for carboxylic acid activation, protection, and or coupling fail with a particular compound or set of compounds, the fallback position is to carry out the coupling reaction at the bench. To this end, protecting groups for amines and carboxylic acids are put in place so that, as with the Merrifield method, the free amino group of one amino acid or peptide fragment, protected at the carboxylate, is available to react with the activated carboxylate of... 

The following short descriptions of the steps involved in the synthesis of a tripeptide will demonstrate the complexity of the problem amino acid units. In the later parts of this section we shall describe actual syntheses of well defined oligopeptides by linear elongation reactions and of less well defined polypeptides by fragment condensation. 

Total syntheses have been reported by E.J. Corey (1978B, 1979). We outline only the stereoselective synthesis of a protected fragment (A) which contains carbon atoms 1—9. This fragment was combined with fragment (B) by a Grignard reaction and cyclized by one of the methods typical for macrolide formation (see p. 146). 

The 9 — 15 fragment was prepared by a similar route. Once again Sharpless kinetic resolution method was applied, but in the opposite sense, i.e., at 29% conversion a mixture of the racemic olefin educt with the virtually pure epoxide stereoisomer was obtained. On acid-catalysed epoxide opening and lactonization the stereocentre C-12 was inverted, and the pure dihydroxy lactone was isolated. This was methylated, protected as the acetonide, reduced to the lactol, protected by Wittig olefination and silylation, and finally ozonolysed to give the desired aldehyde. 

The (partial) description of the synthesis and coupling of the five fragments starts with the cyclohexyl moiety C —C. The first step involved the enantio- and diastereoselective harpless epoxidation of l,4-pentadien-3-ol described on p. 126f. The epoxide was converted in four steps to a d-vinyl d-lactone which gave a 3-cyclohexenecarboxylate via Ireland-CIaisen rearrangement (cf. p. 87). Uncatalysed hydroboration and oxidation (cf. p. 131) yielded the desired trans-2-methoxycyclohexanol which was protected as a silyl ether. The methyl car-... 

A great deal of experimental work has also been done to identify and quantify the ha2ards of explosive operations (30—40). The vulnerabiUty of stmctures and people to shock waves and fragment impact has been well estabUshed. This effort has also led to the design of protective stmctures superior to the conventional barricades which permit considerable reduction ia allowable safety distances. In addition, a variety of techniques have been developed to mitigate catastrophic detonations of explosives exposed to fire. 

These methodologies have been reviewed (22). In both methods, synthesis involves assembly of protected peptide chains, deprotection, purification, and characterization. However, the soHd-phase method, pioneered by Merrifield, dominates the field of peptide chemistry (23). In SPPS, the C-terminal amino acid of the desired peptide is attached to a polymeric soHd support. The addition of amino acids (qv) requires a number of relatively simple steps that are easily automated. Therefore, SPPS contains a number of advantages compared to the solution approach, including fewer solubiUty problems, use of less specialized chemistry, potential for automation, and requirement of relatively less skilled operators (22). Additionally, intermediates are not isolated and purified, and therefore the steps can be carried out more rapidly. Moreover, the SPPS method has been shown to proceed without racemization, whereas in fragment synthesis there is always a potential for racemization. Solution synthesis provides peptides of relatively higher purity however, the addition of hplc methodologies allows for pure peptide products from SPPS as well. 

Enameling meets decorative as weU as protective requirements. Ceramic enamels are mainly based on alkaH borosiHcate glasses. The part to be enameled is dipped into or sprayed with a sHp, ie, a water suspension of glass fragments called frit. The sHp coating is dried and fused in an enameling furnace under careful heat control (see Enamels, porcelain or vitreous). 

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