Mercaptoethanols reactions with

The dinitrophenyl group has been used to protect the imidazole — NH group in histidines (45% yield)" by reaction with 2,4-dinitrofluorobenzene and potassium carbonate. Imidazole —NH groups, but not a-amino acid groups, are quantitatively regenerated by reaction with 2-mercaptoethanol (22°, pH 8, 1 h)." The 2,4-... 

Hemithioketals can be prepared from 12,20-diketones [e.g., (81)] by reaction with mercaptoethanol, zinc chloride and sodium sulfate in dioxane. The 12-hemithioketal of triketocholanic acid is prepared by selective cleavage of the 3,7,12-trihemithioketal. " ... 

FIGURE 5.18 Methods for cleavage of disulfide bonds in proteins, (a) Oxidative cleavage by reaction with performic acid, (b) Reductive cleavage with snlfliydryl compounds. Disulfide bridges can be broken by reduction of the S—S link with snlfliydryl agents such as 2-mercaptoethanol or dithiothreitol. Because reaction between the newly reduced —SH groups to re-establish disulfide bonds is a likelihood, S—S reduction must be followed by —SH modification (1) alkylation with iodoac-etate (ICH,COOH) or (2) modification with 3-bromopropylamine (Br— (CH,)3—NH,). 

Second-order rate constants for MTSEA-, MTSET-, and MTSES-modification of residues within the loop D region of the GABA-binding site. Second-order rate constants (IC2) represent the mean standard deviation. NR, no reaction. The free solution rates were reported by Karlin and Akabas (1998) and reflect the rates of MTS reaction with 2-mercaptoethanol. Adapted from Holden and Czajkowski (2002) with permission from the American Society of Biochemistry and Molecular Biology... 

To further exploit the potential usefiilness of this new family of clusters, monoadduct 54 was saponified into 55 (0.05 M NaOH, quant) and condensed to L-lysine methyl ester using 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline (EEDQ) to give extended dimer 56 in 50 % yield together with monoadduct in 15 % yield [75]. Additionally, tert-butyl thioethers 52 could be transformed into thiols by a two step process involving 2-nitrobenzenesulfenyl chloride (2-N02-PhSCl, HOAc, r.t, 3h, 84%) followed by disulfide reduction with 2-mercaptoethanol (60%). Curiously, attempts to directly obtain these thiolated telomers by reaction with thioacetic acid f ed. These telomers were slightly better ligands then lactose in inhibition of binding of peanut lectin to a polymeric lactoside [76]. 

Carbonic anhydrase activities of the egg shells are inhibited by reaction with p-mercuribenzoate by blocking reactive SH-groups of the enzyme. Omission of 2-mercaptoethanol from buffer solutions for extraction and fractionation also resul-... 

Oxathiolanes (11) are formed from aldehydes and ketones by reaction with 2-mercaptoethanol (HS-CH2-CH2OH) in the presence of, for example, zinc chloride-sodium acetate in dioxane solution at room temperature,139 or boron trifluoride-etherate.140 They are more stable to an acidic medium than the 1,3-dithianes, and therefore may be the protective group of choice in certain instances. 

Fluorimetric methods for the determination of amino acids are generally more sensitive than colorimetric methods. Fluorescamine (4-phenyl-spiro[furan-2(3H),l -phthalan]-3,3 -dione) and o-phthaldialdehyde (OPA) substances are used for protein analysis. Fluorescamine reacts with amino groups to form fluorophores that excite at 390 nm and emit at 475 nm (Weigele et al., 1972). Applications of fluorescamine include monitoring the hydrolysis of K-casein (Beeby, 1980 Pearce, 1979) and quantification of proteins, peptides, amino acids in extracts (Creamer et al., 1985). OPA produces fluorescence on reaction with 2-mercaptoethanol and primary amines, with strong absorption at 340 nm. Lemieux et al. (1990) claimed that this method was more accurate, convenient, and simple for estimating free amino acids than the TNBS, ninhydrin, or fluorescamine methods. 

The 5,6-dihydro-2 -deoxyuridin-6-yl was generated specifically by photolyzing the respective tertiary butyl ketone (Carter and Greenberg 2003). It reacts fast with 2-mercaptoethanol [reaction (150) k = 8.8 x 106dm3 mol-1 s 1] and noticeably slower with 2,5-dimethyltetrahydrofurane (31 dm3 mol1 s ). In the presence of 02, 6-hydroxy-5,6-dihydro-dUrd is the major product [reactions (151) and (152)]. Interestingly, 2-dRL is also formed under such conditions which is believed to be formed by an intramolecular C(l )-H abstraction via a six-membered transition state [reaction (153) for this type of reaction see also Chap. 8.6],... 

Although DTT is not necessary in the enzymatic conversion of penicillin G [14], this compound is known to stimulate the expandase activity of frozen crude extracts of S. clavuligerus and C. acremonium on penicillin N [40], However, neither this reagent nor P-mercaptoethanol was able to stimulate the subsequent reaction with penicillin G when added during preincubation with FeS04 and ascorbate [43],... 

Miles and Moye [171] have shown that several classes of nitrogen containing pesticides responded to a high performance liquid chromatography post-column reaction detector that employed ultraviolet photolysis with optional reaction with o-phthalicdicarboxaldehyde-2-mercaptoethanol followed by fluorescence detection. It was applied to the determination of jV-methylcarbamates, carbamoyl oximes, carbamethoic acids, dithiocarbamates and phenyl ureas, phenyl amides and phenyl carbamates in groundwater. See also Table 4.3. 

In a dramatic demonstration of the use of a scavenger Nicolson et al. (1982) demonstrated that a long-lived intermediate formed when p-azi-do[3H]puromycin was used to label F.. coli ribosomes was diverted from its reaction with polypeptide SI8 by 2 mM P-mercaptoethanol. SI8 was the... 

Atkinson, J., Morand, P., Arnason, J. T., Niemeyer, H. M. and Bravo, H. R. 1991. Analogues of the cyclic hydroxamic acid 2,4-dihydroxy-2H-1,4-benzoxazin-3-one decomposition to benzoxazolinones and reaction with -mercaptoethanol. J. Org. Chem. 56, 1788-1800... 

Especially useful is the reaction of carbodiimides with 2-mercaptoethanol because rapid reaction with EDC occurs with rates similar to the reaction of carboxyl groups with EDC. °... 

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