Azides functional groups

Although photoreactive aryl azides are relatively inert to thermochemical reactions prior to photolysis, they are not stable in the presence of sulfhydryl compounds, which can reduce the azide functional group to an amine. Avoid, therefore, the use of reduc-tants such as DTT or 2-mercaptoethanol before the photolyzing step, as these can react with the aryl azide within minutes (Staros et al., 1978). Avoid also amine-containing... 

Since the active ester end of the molecule is subject to hydrolysis (half-life of about 20 min in phosphate buffer at room temperature conditions), it should be coupled to an amine-containing protein or other molecule before the photolysis reaction is done. During the initial coupling procedure, the solutions should be protected from light to avoid decomposition of the phenyl azide functional group. The degree of derivatiza-tion should be limited to no more than a 5- to 20-fold molar excess of sulfo-SBED over the quantity of protein present to prevent possible precipitation of the modified molecules. For a particular protein, studies may have to be done to determine the optimal level of modification. 

One Cascade Blue derivative is available for creating linkages with amine-containing molecules. The acetyl azide functional group of this reagent reacts with primary... 

Spectroscopic analysis revealed that the thermally initiated [3 + 2] polycycloaddition produced 1,4- and 1,5-substituted triazole isomers in an approximately 1 1 ratio. This ratio appears to be statistic and dependant on the bulkiness of the organic moieties. For example, hfr-r-P[30(4)-20] with butyl spacers contained slightly more 1,4-triazole isomers than did hb-r-P[30(6)-20] with hexyl spacers. This becomes clearer if we look at the proposed transition states a and b of the [3 + 2]-dipolar cycloaddition (Scheme 16). Because of their molecular orbital symmetry, the acetylene and azide functional groups arrange in two parallel planes, a so-called two-plane orientation complex [48], which facilitates a concerted ring formation. If the monomer fragment or the polymer branch ( ) attached to the functional groups are bulky, steric repulsion will come into play and transition state a will be... 

Figure 10-8 MOE facilitates glycomic technologies. As discussed in detail in the text (and the references cited), the MOE analog AcaGIcNAz can be used to incorporate biologically orthogonal azide functional groups into cellular proteins that can then be exploited to separate, visualize, and identify the host glycoprotein.

Interestingly, dimer 13 has increased cytotoxicity compared to 4 and 6-11, with an ED5o in the 0.2-0.4 pg/ml range against the same tumour cell lines. Presumably, this increase is a nonspecific effect caused by the presence of the toxic azide functional group. 

In the final stages of the synthesis (Scheme 21), the dimerization protocol developed earlier (Scheme 5, vide supra) was followed, with the slight modification that triphenyltin hydride was used for reduction of the azide functional group. Cyclization of the a-aminoketone with PPTS afforded dimer 46 in 79 % yield, accompanied by 17 % of deazidoketone monomer. Removal of the... 

Several reports have been made using this reaction as a protein bioconjugation technique. In the first report, 60 azide functional groups attached to the surface of the cowpea mosaic virus (CPMV) using NHS ester or iodoacetamide reactions served as attachment sites for fluorescent alkyne derivatives [92]. The optimal conditions for the reaction were 21 pM protein (based on azide-functionalized capsid monomers), 1 mM CuS04, 2 mM TCEP, and 2 mM 58 in pH 8 buffer at 4°C for 16 h. As an alternative, small amounts of copper wire were also effective in generating and maintaining the Cu(I) species. The reaction was also successful when the alkynes were attached to the viral capsid and azides were attached to the dye. 

Figure 2.12 DNA crosslinking. The deleterious properties of nitrogen mustards are explained through the illustrated interstrand linkage mechanism that makes DNA impossible to duplicate or transcribe. Intrastrand crosslinking is the basis of action for anti-cancer drugs such as c/s-platin and carbo-platin. This is intended to prevent DNA duplication and hence cancer cell division. DNA crosslinking to proteins (such as histones) uses a non-covalent DNA intercalator with two azide functional groups. Both azides are activated for covalent coupling under photo-chemical conditions so that DNA subsequently becomes covalently linked to protein.

Sodium azide may be analyzed by reacting the aqueous solution with iodine. The reaction is induced by 2-mercaptopyrimidine (Kurzawa 1987). The excess of iodine is back-titrated using potassium iodide, sodium thiosulfate, and starch indicator. The azide functional group may be identified by FTIR. 

The azide functional group is therefore a convenient precursor to primary amines. The amine formed may further react with other functional groups under the reaction conditions. Thus, the reduction of azido diester 107 provided pyrrolidone 108 after cyclization... 

A number of unimolecular alkoxyamines containing alkyne or azide functional groups have also been reported and used in postpolymerization Huisgen cycloaddition reactions. Gungor et reported an alkyne-functionalized... 

The first method makes use of a modified Staudinger reduction in which a probe containing an azide functional group is reduced and subsequently... 

To avoid decomposition of the sensitive 2-hydroxy azide side chain with Lewis acid, the azide functional group was reduced to amine. These conditions also deprotected the carboxy terminus. After TBS deprotection in acidic conditions, the 2-amino alcohol was treated with excess BBtj for deprotection of Cbz (benzyloxycarbonyl) and OMe groups. Synthesis of biphenomycin B 53 was completed in 14 steps affording 15% overall isolated yield. 

The azide functional group (Problem 2.55), such as occurs in azidobenzene, contains three adjacent nitrogen atoms. One resonance structures for azidobenzene is shown. Draw three additional resonance structures, and assign appropriate formal charges to the atoms in all four. 

Finally, another important class of Si-N linkages consists in the azide modified Si surface (Si-N ), which can again be prepared from either Si-Cl or Si-H surfaces. Direct grafting of azide functional groups on monochloride-covered (111) Si surfaces can be obtained by a room temperature treatment with NaN in either hexamethyl-phosphoramide (HMPA) or methanol for 5 min and 3 h, respectively [217]. 

---