Free amino groups

Another important method of following protein hydrolysis is that due to Van Slyke, and consists in estimating the free amino groups liberated by treatment with nitrous acid, whereby gaseous nitrogen is evolved and measured in a special apparatus. 

Then N-Boc-O-benzylserine is coupled to the free amino group with DCC. This concludes one cycle (N° -deprotection, neutralization, coupling) in solid-phase synthesis. All three steps can be driven to very high total yields (< 99.5%) since excesses of Boc-amino acids and DCC (about fourfold) in CHjClj can be used and since side-reactions which lead to soluble products do not lower the yield of condensation product. One side-reaction in DCC-promoted condensations leads to N-acylated ureas. These products will remain in solution and not reaa with the polymer-bound amine. At the end of the reaction time, the polymer is filtered off and washed. The times consumed for 99% completion of condensation vary from 5 min for small amino acids to several hours for a bulky amino acid, e.g. Boc-Ile, with other bulky amino acids on a resin. A new cycle can begin without any workup problems (R.B. Merrifield, 1969 B.W. Erickson, 1976 M. Bodanszky, 1976). 

The most used EIA reagents conjugate a fluotophote such as fluorescein-isothiocyanate (EITC) or thodarnine—isothiocyanate to antibody (or antigen) free amino groups. Examples of other commonly used fluotophotes for EIA and their spectral characteristics ate presented in Table 3. EIA assays ate available in sandwich and competitive formats similar to EIAs. Unlike EIA kits which can be used directly with visual color deterrnination, EIAs require a fluorometer, and thus ate primarily laboratory-based. 

Sympathomimetics with free amino groups e g carbadrine, norfenefnne, noradrenaline, norephednne... 

Section 27.17 Peptide bond fonnation between a protected amino acid having a free carboxyl group and a protected amino acid having a free amino group can be accomplished with the aid of A, A/ -dicyclohexylcaibodiimide (DCCI). 

Molecules of interest that contain free amino groups can be coupled in aqueous solution to /S-poIy(L-malate) as amides using carbodiimides such as the water-soluble l-ethyl-3(3-dimethyIaminopropyl)carbodiimide hydrochloride (EDC) [2,12,20,21]. By this method, the molecules are attached randomly. A selective amide bond formation at the carboxylate terminus can be achieved... 

Peptide synthesis requires the use of selective protecting groups. An N-protected amino acid with a free carboxyl group is coupled to an O-protected amino acid with a free amino group in the presence of dicydohexvlcarbodi-imide (DCC). Amide formation occurs, the protecting groups are removed, and the sequence is repeated. Amines are usually protected as their teit-butoxy-carbonyl (Boc) derivatives, and acids are protected as esters. This synthetic sequence is often carried out by the Merrifield solid-phase method, in which the peptide is esterified to an insoluble polymeric support. 

In most cases the microspheres were insoluble. The polysaccharides might be partially cross-linked via amido groups formed by the carboxyl groups of the polyanion and the restored free amino group of chitosan. The susceptibility to enzymatic hydrolysis by lysozyme was poor, mainly because lysozyme, a strongly cationic protein, can be inactivated by anionic polysaccharides [207]. 

Heteroarylphenylalanines could be smoothly obtained via microwave-promoted Suzuki reaction of heteroaryl halides with 2-amino-3-[4-(dihy-droxyboryl)phenyl]propanoic acid (Scheme 28) [46]. Interestingly, the free amino acid could be used without any protection of the amine and carboxylic acid fimctionahty. When 4-(dihydroxyboryl)-L-phenylalanine was used as organometallic partner no racemization was observed. The carboxylate anion and free amino group seem to shield the a-C - H from deprotonation and thus hmit racemization. 

Andry, M. C., Edwards-Levy, F. Levy, M. C. (1996). Free amino group content of serum albumin microcapsules. III. A study at low pH values. International Journal of Pharmaceutics, Vol. 128,1-2, (February 1996), pp. (197-202), ISSN 0378-5173... 

Phenyliodonium ylids of cyclic dicarbonyl compounds (46) react with thiourea to form the thiouronium ylid (47) which on heating is converted into the fused thiazole (48), this method is applicable to subtituted thioureas provided they have at least one free amino group. This reaction can be considered to be a modification of the Hantzsch thiazole synthesis <96JHC575>. 

The reduction is carried out in acetic anhydride so that amine (11) is acetylated as it is formed. This prevents the free amino group attacking the esters. 

The free amino group of the amino ester may then react analogously with another molecule of the monomer, etc. The kinetics of the polymerization are in harmony with a mechanism of this sort. The final polypeptide may contain up to 300 or more structural units. While the polymerization of N-carboxyanhydrides is closely analogous to the addition polymerizations of ethylene oxide and of other cyclic substances, definition unfortunately classifies it as a condensation polymerization inasmuch as carbon dioxide is eliminated in the process. 

Figure 20. Selective cell targeting via specific monoclonal antibodies and/or antibody fragments directed against cancer cells and linked to the free amino groups of L-cysteine-coated metallic-core magnetic nanoparticles (MNP) (MNP = Co, Fe/Co, size 8-10 nm).

Lipids with free amino groups appear as red-violet spots... 

In contrast to MDA and hydroxynonenai, other aldehyde products of lipid peroxidation are hydrophobic and remain closely associated with LDL to accumulate to mil-limolar concentrations. Aldehydes at these elevated levels react with the protein portion of the LDL molecule, apolipoprotein B (apoB). Accumulated aldehydes bind the free amino groups from lysine residues in addition to other functional groups (-OH, -SH) on the apoB polypeptide. Consequently, the protein takes on a net negative charge and complete structural rearrangement results in the formation of ox-LDL. ox-LDL is no longer recognized by the LDL receptor, and has several pro-inflammatory properties (discussed below). 

---