Acid Protection

Bakery Products. Sorbates are used in and/or on yeast-raised and chemically leavened bakery products. The internal use of sorbates in yeast-raised products at one-fourth the amount of calcium—sodium propionate that is normally added provides a shelf life equal to that of propionate without adversely affecting the yeast fermentation. Sorbates added at one-tenth the propionate level reduce the mix time by 30% (126). This internal treatment combined with an external spray of potassium sorbate can provide the same or an increased shelf life of pan breads, hamburger and hot-dog buns, English muffins, brown-and-serve roUs, and tortillas. The total sorbate useful in or on these baked goods ranges from 0.03 wt % for pan breads to 0.5 wt % for tortillas 0.2—0.3 wt % sorbic acid protects chemically leavened yellow and chocolate cakes (127). Emit-pie fillings and icings can be protected with 0.03—0.1 wt % sorbates. 

Oxazoles, prepared from carboxylic acids (benzoin, DCC NH4OAC, AcOH, BOSS % yield), have been used as carboxylic acid protective groups in a variety of synthetic applications. They are readily cleaved by singlet oxygen followed by hydrolysis (ROH, TsOH, benzene or K2CO3, MeOH ). 

The Noc group, developed for amino acid protection, is introduced with the acid chloride (Et3N, H2O, dioxane, 2 h, 20°, 61-95% yield). It is cleaved with Pd(Ph3P)4 (THF, A, A -dimethyibarbituric acid, 8 h, 20°, 80% yield). It is not isomerized by Wilkinson s catalyst, thus allowing selective removal of the allyl ester group. 

Anodic protection is particularly suitable for stainless steels in acids. Protection potential ranges are given in Section 2.4. Besides sulfuric acid, other media such as phosphoric acid can be considered [13,21-24]. These materials are usually stable-passive in nitric acid. On the other hand, they are not passivatable in hydrochloric acid. Titanium is also a suitable material for anodic protection due to its good passivatability. 

The heptyl ester was developed as an enzymatically removable protective group for C-terminal amino acid protection. 

Dimethyl-3-pentanoL DCC, DMAP, CH2CI2, 4 h. This group was developed as an improvement over the use of cylcohexanol for aspartic acid protection during peptide synthesis. ... 

The Dmab group was developed for glutamic acid protection during Fmoc/r-Bu based peptide synthesis. The group shows excellent acid stability and stability toward 20% piperidine in DMF. It is formed from the alcohol using the DCC protocol for ester formation and is cleaved with 2% hydrazine in DMF at rt. ... 

In a rather nontraditional approach to acid protection, the tetraalkylammonium salts of amino acids allow for coupling of HOBt-activated amino acids in yields of 55-84%. ... 

The Paloc group was developed as an amino acid protective group that is introduced with the p-nitrophenyl carbonate (H2O, dioxane, 68-89% yield). It is exceptionally stable to TFA and to rhodium-catalyzed allyl isomerization, but it is conveniently cleaved with Pd(Ph3P)4 (methylaniline, THF, 20°, 10 h, 74-89% yield). ... 

An alternate route to ampicillin not only circumvents the need for 6-APA but also has the advantage of providing a prodrug form of ampicillin as well as the parent compound. Reaction of benzylpenicillin (4) with the acid protecting group, 29, gives the formol ester, 30. Reaction of the product with phosphorus pentachloride leads to the corresponding imino chloride (31). 

Spherical vaterite crystals were obtained with 4-mercaptobenzoic acid protected gold nanoparticles as the nucleation template by the carbonate diffusion method [51]. The crystallization of calcium carbonate in the absence of the 4-MBA capped gold nanoparticles resulted in calcite crystals. This indicates that the polymorphs of CaCOj were controlled by the acid-terminated gold nanoparticles. This result indicates that the rigid carboxylic acid structures can play a role in initiating the nucleation of vaterite as in the case of the G4.5 PAMAM dendrimer described above. 

Meadows, J., Smith, R.C. and Reeves, J. (1986). Uric acid protects membranes and linolenic acid from ozone-induced oxidation. Biochem. Biophys. Res. Commun. 137, 536-541. 

Fraga, C.G., Motchnik, P.A., Shigenaga, M.K., Helbock, H.J., Jacob, RA. and Ames, B.N. (1991). Ascorbic acid protects against endogenous oxidative DNA damage in human sperm. Proc. Natl Acad. Sci. USA 88, 11006-11033. 

In general, the methods for protection and deprotection of carboxylic acids and esters are not as convenient as for alcohols, aldehydes, and ketones. It is therefore common to carry potential carboxylic acids through synthetic schemes in the form of protected primary alcohols or aldehydes. The carboxylic acid can then be formed at a late stage in the synthesis by an appropriate oxidation. This strategy allows one to utilize the wider variety of alcohol and aldehyde protective groups indirectly for carboxylic acid protection. 

Buu Hoi and Ratsimamanga116 found that kojic acid protected the adrenal ascorbic acid in test animals during the reversible period of scurvy, without itself showing vitamin C action. 

Stine, E.R., C.A. Hsu, T.D. Hoovers, H.V. Aposhian, and D.E. Carter. 1984. N-(2,3-dimercaptopropyl) phthal-amidic acid protection, in vivo and in vitro, against arsenic intoxication. Toxicol. Appl. Pharmacol. 75 329-336. 

L Lapatsanis, G Milias, K Froussios, M Kolovos. Synthesis of A-2,2,2,-(trichloro-ethoxy carbonyl)-L-amino acids and A-(fluorenylmethoxycarbonyl)-L-amino acids involving succinimidoxy anion as a leaving group in amino acid protection. Synthesis 671, 1983. 

Bisaglia M, Natalini B, Pellicciari R, Straface E, Malorni W, Monti D, Franceschi C, Schettini G (2000) C3-fullero-tris-methanodicarboxylic acid protects cerebellar granule cells from apoptosis. J. Neurochem. 74 1197-1204. 

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