Sulfation and amidation

Amidation refers to the replacement of a protein s C-terminal carboxyl group with an amide group (COOH — CONH2). This PTM is usually characteristic of peptides (very short chains of amino acids), as opposed to the longer polypeptides, but one therapeutic polypeptide (salmon calcitonin, Chapter 11) is amidated, and amidation is required for full functional activity. Overall, the function(s) of amidation is not well understood, although in some cases at least it appears to contribute to peptide/polypeptide stability and/or activity. 

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Although soaps have many physical properties in common with the broader class of surfactants, they also have several distinguishing factors. First, soaps are most often derived direcdy from natural sources of fats and oils (see Fats and fatty oils). Fats and oils are triglycerides, ie, molecules comprised of a glycerol backbone and three ester-linked fatty oils. Other synthetic surfactants may use fats and oils or petrochemicals as initial building blocks, but generally require additional chemical manipulations such as sulfonation, esterification, sulfation, and amidation. 

Many polypeptides undergo covalent modification after (or sometimes during) their ribosomal assembly. The most commonly observed such PTMs are listed in Table 2.7. Such modifications generally influence either the biological activity or the structural stability of the polypeptide. The majority of therapeutic proteins bear some form of PTM. Although glycosylation represents the most common such modification, additional PTMs important in a biopharmaceutical context include carboxylation, hydroxylation, sulfation and amidation these PTMs are now considered further. 

Fats and oils are renewable products of nature. One can aptly call them oil from the sun where the sun s energy is biochemically converted to valuable oleochemicals via oleochemistry. Natural oleochemicals derived from natural fats and oils by splitting or tran -esterification, such as fatty acids, methyl esters, and glycerine are termed basic oleochemicals. Fatty alcohols and fatty amines may also be counted as basic oleochemicals, because of their importance in the manufacture of derivatives (8). Further processing of the basic oleochemicals by different routes, such as esterification, ethoxylation, sulfation, and amidation (Figure 1), produces other oleochemical products, which are termed oleochemical derivatives. 

PTMs are often observed in the conotoxin sequence and are thought to contribute to the diversity of a-conotoxins. One such PTM is the sulfation of a tyrosine residue, found in EpI, PnIA, PnIB, AnIA, AnIB, and AnlC. Although the function of this tyrosine sulfation is currently not known, it may improve the stability or solubility of the protein. Tyrosine sulfation and amidation improve the activity of AnIB at the al nAChR subtype, indicating that PTMs may aid subtype selectivity. ... 

Chem. Descrip. Proprietary blend of surfactants, sulfates, and amides Uses Cone, for hand dish wash llqs. offers low vise., thermal stability, low Irritation, cold letdown, ease of handling... 

To a vigorously stirred suspension of 2 mol of lithium amide in 2 1 of liquid atimonia (see II, Exp. 11) was added in 15 min 1 mol of propargyl alcohol (commercial product, distilled in a partial vacuum before use). Subsequently, 1 mol of butyl bromide was added dropwise in 75 min. After an additional 1.5 h, stirring was stopped and the ammonia was allovied to evaporate. To the solid residue were added 500 ml of ice-water. After the solid mass had dissolved, six extractions with diethyl ether were performed. The (unwashed) combined extracts were dried over magnesium sulfate and then concentrated in a water-pump vacuum. Distillation of the residue through a 40-cm Vigreux column afforded 2-heptyn-l-ol, b.p. 

Sulfated Acids, Amides, and Esters. Reaction with sulfuric acid may be carried out on fatty acids, alkanolamides, and short-chain esters of fatty acids. The disodium salt of sulfated oleic acid is a textile additive and an effective lime soap dispersant. A typical sulfated alkanolamide stmcture is CiiH23C0NHCH2CH20S03Na. Others include the sulfates of mono and diethanolamides of fatty acids in the detergent range. The presence of... 

The influence of other groups in a pyridine or similar ring system is more difficult to assess because no kinetic data are available. The deactivating effect of the bromine atom in the 2-position is greater than that in the 3-position, while 2,6-dibromopyridine is very slow to react with dimethyl sulfate. Esters, amides, and nitriles of nicotinic and isonicotinic acids undergo fairly easy quaternization at about... 

A solution of 3 g of the nitrile, water (5 moles per mole of nitrile), and 20 g of boron trifluoride-acetic acid complex is heated (mantle or oil bath) at 115-120° for 10 minutes. The solution is cooled in an ice bath with stirring and is carefully made alkaline by the slow addition of 6 A sodium hydroxide (about 100 ml). The mixture is then extracted three times with 100-ml portions of 1 1 ether-ethyl acetate, the extracts are dried over anhydrous sodium sulfate, and the solvent is evaporated on a rotary evaporator to yield the desired amide. The product may be recrystallized from water or aqueous methanol. Examples are given in Table 7.1. 

According to U.S. Patent 2,676,964 to 1.0 mol of potassium amide in 3 liters of liquid ammonia, is added 1.0 mol of 2-benzylpyridine. After 15 minutes, 1.1 mols of 3reaction product decomposed with water and ether extracted. The ether layer is dried over Sodium sulfate and after evaporation the residue is distilled, giving the 3-phenyl-3-(2-pyridyl)-N,N-dimethylpropylamine, BP 139°-142°C/1-2 mm. The maleate is produced by reaction with maleic acid. 

To a suspension of 3.9 grams of potassium amide is slowly added a solution of 19.2 grams (0.1 mol) Of 5H-dibenzo[a,d] cycloheptene in 600 ml of ether with stirring. The suspension is refluxed with stirring for 3 hours, then cooled to room temperature and a solution of 0.1 mol of 3-(N-formyl-N-methyl)-aminopropyl chloride in 100 ml of ether added. The mixture is then refluxed with stirring for 5 hours and then 100 ml of water added. The ether layer is then washed with dilute hydrochloric acid, then water and then dried over magnesium sulfate and evaporated to dryness yielding 5-[3-(N-formyl-N-methyl)-amino-propyl] -5H-dibenzo[a,d] cycloheptene. 

Benzyl cyanide is first reacted with 2-butylbromide in the presence of sodium amide to give 2-phenyl-3-methylvaleronitrile which is hydrolyzed by sulfuric acid to give 3-methyl-2-phenyl-pentanoic acid. 24 g of 2-phenyl-3-methyl-pentanoic acid are heated for one hour at 175° to 185°C with 30 g of 2-diethylaminoethanol and 0.5 g of sodium methylate. The excess diethyl-aminoethanol is removed in vacuo, the residue is dissolved in 300 cc of 2 N-acetic acid, the acid solution is shaken with ether and made alkaline with concentrated potassium carbonate solution and ice. The ether solution Is washed with water, dried with sodium sulfate and evaporated. The residue is distilled under high vacuum, yielding 20 to 21 g of the basic ester (60% of the theoretical) is obtained, the ester boiling at 98° to 100°C at a pressure of 0.03 mm. The hydrochloride of the ester melts at 112° to 113°C and the methobromide at 100° to 101°C. 

Table 6 shows a comparison of commercially produced C, 4 LAS samples in a current North American light-duty liquid (LDL) formulation containing more than 20% LAS together with alcohol ether sulfate (AES), amide, and hydrotrope. The highest viscosity is observed with the high 2-phenyl/low DATS sample, whereas the high 2-phenyl/high DATS sample had the lowest viscosity. The DATS provides the dual function of surfactant and hydrotrope. 

Chromium(III) is a commonly-used crosslinker for preparing profile control gels with polymers having carboxylate and amide functionalities (la,b). Cr(III) is applied in many forms. For example, it can be used in the form of simple chromic salts of chloride and sulfate, or as complexed Cr(III) used in leather tanning (2), or as in situ generated Cr(III) from the redox reaction of dichromate and bisulfite or thiourea. The gelation rate and gel quality depend on which form of Cr(III) is used. 

Methylation of X with silver oxide and methyl iodide gave the lactone of methyl 2,5-dimethyl-j8-D-glucofururonoside (XIII) which was characterized by its conversion to the crystalline amide (XIV). Further methylation of XIII, form, with methyl sulfate and sodium hydroxide gave methyl 2,3,5-trimethyl-/3-D-glucofururonoside (XVI) from which by hydrolysis of the glycosidic methyl group and subsequent oxidation with bromine, there was obtained 2,3,5-trimethyl-D-glucosaccharolactone (XVII) characterized by the formation of its crystalline methyl ester. 

The mother liquors and the two washes containing methanol are collected and combined. A one normal solution of potassium hydroxide in methanol is added in approximately equal volume to the combined washes and mother liquors. The solution is then filtered and the filter washed with a few ml of methanol. The filtrates are allowed to stand at room temperature for two to three hours to reequilibrate the iso-lysergic acid amides from the mother liquors. About 500 ml of water is then added and the mixture extracted with 2.5 liters of methylene chloride in divided portions in a separatory funnel. The combined extracts are shaken with 25 grams of anhydrous magnesium sulfate and filtered. The filtrate is taken to dryness on the rotary vacuum evaporator, care taken not to heat above 55° C. The material is purified in the same manner as that from the original reaction mixture using approximately one fourth the quantities of solvents and alumina as for the original. 

Many drugs have functional groups that can be metabolized by the addition of water. The major functional groups involved are esters, amides, and epoxides. Several phase II metabolites such as sulfates and glucuronides, which will be discussed in Chapter 7, can also be hydrolyzed back to the parent drug. 

The dimer of chloro(l,5-hexadiene)rhodium is an excellent catalyst for the room temperature hydrogenation of aromatic hydrocarbons at atmospheric pressure. The reaction is selective for the arene ring in the presence of ester, amide, ether and ketone functionalities (except acetophenone). The most useful phase transfer agents are tetrabutylammonium hydrogen sulfate and cetyltrimethylammonium bromide. The aqueous phase is a buffer of pH 7.6 (the constituents of the buffer are not critical). In all but one case the reaction is stereospecific giving cis products... 

The most common posttranslational modifications, discussed in the following sections, include phosphorylation, sulfation, disulfide formation, N-methylation, O-methylation, S-methylation, N-acetylation, hydroxylation, glycosylation, ADP-ribosylation, prenylation, biotinylation, lipoylation, and phosphopan-tetheine tethering. Many of the posttranslational modifications are proven to be cross talks. Other modifications exist in a smaller extent and include oxidation of methionine, C-methylation, ubiquitylation, carboxylation, and amidation. These topics will not be covered in this chapter which is meant to focus primarily on the recent literature (2005-08). For a more complete coverage of all posttranslational modifications and earlier literature (up to 2005), the reader is referred to Professor Christopher T. Walsh s book Posttranslational Modification of Proteins Expanding Nature s Inventory ... 

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