Acetyl protected thiols

In the thiol 79 and the sulfinic acid 80, two new acidic functionalities are now present in the 2 -position of a m-terphenyl system and should be incorporable into concave structures by a double bridging of the m-terphenyl. For the acetyl-protected thiol 78, the corresponding concave thiol acetate 42 (Scheme 7) could be obtained after tetrabromination of the four methyl groups and bridging with m-phenylenedithiol (see Sect. 2.3). 

In a much simpler system, the outcome of a thioacetate Mitsunobu on a series of hydroxythiol derivatives depended on the nucleophilicity of the neighboring thiol group.Thus, the tert-butylthiol compound 248 gave the trans compound 249 via an intermediate episulfonium ion, whereas the corresponding Boc or acetyl protected thiols 250 gave the desired cis derivatives 251. 

Keywords tert-Butyl protected thiols, hromine, acetyl chloride (AcCl), acetic acid, room temperature, acetyl protected thiols... 

AcCI/AcOH (1 1), rt, 30 min 1 (0.01 mmol) Acetyl protected thiol 2... 

To a well-stirred solution of tert-hvXy protected thiol (1 0.01 mmol) in acetyl chloride (10 mL), a solution of bromine (5 mol%) in acetyl chloride-acetic acid (1 1) was added in 30 minutes at room temperature. After completion of the reaction (1-30 minutes after the bromine addition as monitored by TLC), all solvents were removed by evaporation and the crude residues were purified by sdica gel chromatography to obtain pure 5-acetyl protected thiols 2. The products were characterized on the basis of spectral studies. 

Blaszczyk, A., Elbing, M., and Mayor, M. (2004). Bromine catalyzed conversion of 5- m-butyl groups into versatile and, for self-assembly processes accessible, acetyl-protected thiols. Org. Biomol. Chem., 2, 2722-2724. 

Generally, two different strategies are employed for the formation of SAMs of functional components on gold surfaces. One method is the direct adsorption of a functional component that carries a thiol or disulfide group. This sulfur group is attached to the functional component by a synthetic procedure prior to the SAM formation step (Fig. 7) [27,117-119]. The sulfur group itself may either be a thiol, a disulfide, an acetyl protected thiol or [l,2]-dithiolane. 

Figure 1.69 SAMSA is an anhydride compound containing a protected thiol. Reaction with protein amine groups yields amide bond linkages. Deprotection of the acetylated thiol produces free sulfhydryl groups for conjugation.

SAMSA-fluorescein, 5- [2(and 3)-5-(acetylmercapto)-succinoyl]amino fluorescein, is a fluorescent probe containing a protected sulfhydryl group. In its protected state, the compound is unre-active. The acetyl-protecting group can be removed by treatment with dilute NaOH at pH 10.0 (Figure 9.9). The resulting free sulfhydryl derivative can be used to label thiol-reactive crosslinkers or to couple with sulfhydryl residues on proteins and other molecules. After activating... 

Following preparation of the protected thiol derivative 29 (overall retention of configuration is observed when using Val), a mixed anhydride was prepared and converted into the amide 30 with ammonia. The acetyl group of 30 was then removed and the resulting thiol compound condensed with Z-Arg-OH to give the thioester dipeptide 31. 

Oligonucleotides containing amine groups introduced by enzymatic or chemical means may be modified with SATA (Chapter 1, Section 4.1) to produce protected sulfhydryl derivatives. The NHS ester end of SATA reacts with a primary amine to form a stable amide bond. After modification, the acetyl protecting group can be removed as needed by treatment with hydroxylamine under mildly alkaline conditions (Fig. 401). The result is terminal sulfhydryl groups that can be used for subsequent labeling with thiol-reactive probes or activated-enzyme derivatives (Kumar and Malhotra, 1992). 

Inspection of the literature identified work by Hiskey and Tucker11 who reported the use of iodine to cleave a THP-protected thiol in 1962. Even earlier work by Ratner and Clarke in 1937 demonstrated that thiazolidines can also be cleaved using iodine.12 Both of these reactions give rise to disulfides (Fig. 3). It is interesting to note that Hiskey and Tucker comment that their approach was suggested by the earlier work of Bonner, 13 who in 1948 demonstrated the conversion of acetylated... 

As exemplified by the above case, the HBC nanotubes become totally insoluble after surface polymerization. Hence, reversible polymerization on the nanotube surface is interesting for lithographic patterning. For the realization of this possibility, HBC 4 appended with thiol groups was designed (Figure 1), which can be stitched at the tubularly assembled state by oxidative surface polymerization. The acetyl-protected version of thiol-appended HBC 4 self-assembles in THF to form nanotubes with a diameter of... 

The hydroxy compound 59 has been acetylated (94AJC991), and many glycosides have been protected by acetylation. The 4-thione 209 (85LA1922) and the 3-thiol 210 (83USP4419516) have been alkylated using methyl iodide with potassium hydroxide and chloroacetonitrile with triethylamine respectively. 

Figure 20.6 Available amine groups on an antibody molecule may be modified with the NHS ester end of SATA to produce amide bond derivatives containing terminal protected sulfhydryls. The acetylated thiols may be deprotected by treatment with hydroxylamine at alkaline pH. Reaction of the thiolated antibody with a maleimide-activated enzyme results in thioether crosslinks.

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

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