Amino bifunctional

Willner and coworkers demonstrated three-dimensional networks of Au, Ag, and mixed composites of Au and Ag nanoparticles assembled on a conductive (indium-doped tin oxide) glass support by stepwise LbL assembly with A,A -bis(2-aminoethyl)-4,4 -bipyridinium as a redox-active cross-linker.8 37 The electrostatic attraction between the amino-bifunctional cross-linker and the citrate-protected metal particles led to the assembly of a multilayered composite nanoparticle network. The surface coverage of the metal nanoparticles and bipyridinium units associated with the Au nanoparticle assembly increased almost linearly upon the formation of the three-dimensional (3D) network. A coulometric analysis indicated an electroactive 3D nanoparticle array, implying that electron transport through the nanoparticles is feasible. A similar multilayered nanoparticle network was later used in a study on a sensor application by using bis-bipyridinium cyclophane as a cross-linker for Au nanoparticles and as a molecular receptor for rr-donor substrates.8... 

The use of conventional organic reactions for the cyclization of heterodifunctional linear precursor has also been reported. Macrocycllc PS with DP 20 to 35 was prepared from a-carboxyl,co-amino bifunctional PS through the formation of an amide bond. The linear precursor was synthesized from 3-lithiopropionaldehyde diethylacetal as the functional initiator and 2,2,5,5-tetramethyl-l-(3-bromopropyl)-l-aza-2,5-disilacydopentane as the functional terminating agent. Cyclization was achieved after deprotection under high dilution. ... 

Bis-Pyndoxal Tetraphosphate. A second class of bifunctional reagents, described in 1988, involves two pyridoxal groups linked by phosphates of different lengths (89). As shown in Table 4, the yield of intramolecularly cross-linked hemoglobin increases dramatically with increasing length of the phosphate backbone. It is beheved that the site of reaction of (bis-PL) is between the amino-terminal amino group of one P-chain and the... 

Certain bifunctional nucleophiles allow cyclization after ring opening. The formation of 2-thiazolium salts (71JHC40S) and the analogous production of 2-amino-2-thiazolines (191) from aziridines and thiocyanic acid fall into this category (72JOC4401). 

In Bacillus snbtilis these two reactions are catalyzed by two separate enzymes that have amino acid sequences homologous to the corresponding regions of the bifunctional enzyme from E. coli, and thus each forms a barrel... 

Another type of bifunctional catalysis has been noted with a,cn-diamines in which one of the amino groups is primary and the other tertiary. These substituted diamines are from several times to as much as 100 times more reactive toward imine formation than similar monofunctional amines. This is attributed to a catalytic intramolecular proton transfer. 

The effect of a carboxy group is illustrated by the reactivity of 2-bromopyridine-3- and 6-carboxylic acids (resonance and inductive activation, respectively) (cf. 166) to aqueous acid under conditions which do not give hydroxy-debromination of 2-bromopyridine and also by the hydroxy-dechlorination of 3-chloropyridine-4-car-boxylic acid. The intervention of intermolecular bifunctional autocatalysis by the carboxy group (cf. 237) is quite possible. In the amino-dechlorination (80°, 4 hr, petroleum ether) of 5-carbethoxy-4-chloropyrimidine there is opportunity for built-in solvation (167) in addition to electronic activation. This effect of the carboxylate ion, ester, and acid and its variation with charge on the nucleophile are discussed in Sections I,D,2,a, I,D,2,b, and II,B, 1. A 5-amidino group activates 2-methylsulfonylpyridine toward methanolic am-... 

The catalytic effect of protons, of bifunctional catalysts, and of base is demonstrated in the amination of chloro derivatives of pyridazine, pyrimidine, and s-triazine (Tables V and VI). Anilino-s-triazines containing NH groups act as catalysts in their own formation. The catalytic action of protons on anhino-dechlorination of 2-chloro-4,6-diamino-s-triazine and of 2-amino-4-chloropyrimidine was reported in the classic paper by Banks. ... 

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

As a result of the interaction with bifunctional compounds, e.g., with hexameth-ylenediamine, disubstituted amino groups are formed providing chemical bonds... 

The enantioselective Michael reaction of malonates to nitroolefins catalysed by bifunctional amino-thioureas has recently been reported by Take-moto [161]. Excellent ee (75-93%) were obtained with diethylmalonate after solvent optimisation, toluene being the best solvent both for the activity and for the selectivity. Substituted malonates were then reacted with various nitroolefins under the same conditions. Excellent enantioselectivities were observed (Scheme 45). 

PreUminary studies on the racemic reaction of protected imines with ni-tromethane showed that the thiourea and the amine mutually weakened their reactivities. However, the bifunctional amino-thiourea led to good results. Enantioselectivity of the adduct depended on the protecting group, P(0)Ph2 affording the best results (76% ee). Then, other aromatic imines substrates were successfully phosphorylated with good to high enantioselec-tivities (63-76% ee). 

Bifunctional adamantyl, as a hydrophobic central core, can be used to construct peptidic scaffolding [151], as shown in Fig. 27. This is the reason why adamantane is considered one of the best MBBs. This may be considered an effective and practical strategy to substitute different amino acids or DNA segments on the adamantane core (Fig. 28). In other words, one may exploit nucleic acid (DNA or RNA) sequences as linkers and DNA hybridization (DNA probe) to attach to these modules with an adamantane core. Thus a DNA-adamantane-amino acid nanostructure may be produced. 

As the name implies, an amino acid is a bifunctional molecule with a carboxylic acid group at one end and an amine group at the other. All proteins are polyamides made from condensation reactions of amino acids. Every amino acid in proteins has a central carbon atom bonded to one hydrogen atom and to a second group, symbolized in Figure 13-31 as R. 

PAMAM dendrimers are synthesized in a multistep process. Starting from a multifunctional amine (for example ammonia, ethylenediamine, or tris(2-amino-ethyl)amine) repeated Michael addition of methylacrylate and reaction of the product with ethylenediamine leads to dendrimers of different generation numbers [1,9]. Two methylacrylate monomers are added to each bifunctional ethylenediamine generating a branch at each cycle. Unreacted ethylenediamine has to be completely removed at each step to prevent the initiation of additional dendrimers of lower generation number. Excess methylacrylate has also to be removed. Bridging between two branches of the same or of two different dendrimers by ethylenediamine can also be a problem, and has to be avoided by choosing appropriate reaction conditions. 

The condensation of amino acids likewise may produce cyclic and/or linear products the same is true of virtually all polyfunctional condensation reactions. The conversion of cyclic monomers and dimers (or other cyclic low polymers) to chain polymers was discussed in the preceding chapter the reverse reaction may often occur as well. Thus the alternative ring and chain products which may be produced by condensation of a bifunctional monomer usually are interconvertible, but with varying degrees of facility. 

The principles set forth above account reasonably well for the course of bifunctional condensations under ordinary conditions and for the relative difficulty of ring formation with units of less than five or more than seven members. They do not explain the formation of cyclic monomers from five-atom units to the total exclusion of linear polymers. Thus 7-hydroxy acids condense exclusively to lactones such as I, 7-amino acids give the lactams II, succinic acid yields the cyclic anhydride III, and ethylene carbonate and ethylene formal occur only in the cyclic forms IV and V. 

A second strategy is to attach a linker (also referred to as a handle or anchor) to the resin followed by assembly of the molecule. A linker is bifunctional spacer that serves to link the initial synthetic unit to the support in two discrete steps (Fig. 3). To attach a linker to a chloromethyl-PS resin, a phenol functionality such as handle 4 is used to form an ether bond (Fig. 4). To attach the same handle to an amino-functionalized support, acetoxy function 5 or a longer methylene spacer of the corresponding phenol is applied to form an amide bond. Both of these resins perform similarly and only differ in their initial starting resin [4], An alternative approach is to prepare a preformed handle in which the first building block is prederivatized to the linker and this moiety is attached to the resin. For peptide synthesis, this practice is common for the preparation of C-terminal peptide acids in order to reduce the amount of racemization of the a-carbon at the anchoring position [5],... 

Moreover, Kim and coworkers have shown that a-amino-butyrolactones can be synthesized by a related process employing the amino acid homoserine with an unprotected hydroxy functionality [31]. In a more recent publication by the same research group, morpholin-2-one derivatives of type 9-37 have been prepared (Scheme 9.6) [32]. Herein, glycolaldehyde dimer 9-32 acts as a bifunctional compound, which first reacts with the a-amino acids 9-33 to give the iminium ions 9-34,... 

The cells of all contemporary living organisms are surrounded by cell membranes, which normally consist of a phospholipid bilayer, consisting of two layers of lipid molecules, into which various amounts of proteins are incorporated. The basis for the formation of mono- or bilayers is the physicochemical character of the molecules involved these are amphipathic (bifunctional) molecules, i.e., molecules which have both a polar and also a non-polar group of atoms. Examples are the amino acid phenylalanine (a) or the phospholipid phosphatidylcholine (b), which is important in membrane formation. In each case, the polar group leads to hydrophilic, and the non-polar group to hydrophobic character. 

The bifunctional electrophilic reagent iV-chlorocarbonylisocyanate reacted with 3-amino-5,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methano-l,2,4-benzotriazine 41 followed by treatment with Et3N to give [l,3,5]triazine[l,2- ][l,2,4]-benzotriazine-2,4(377)-dione 21 (Equation 3) <1998JHC293>. 

Pandurangi, R.S. et al. (1998) Chemistry of bifunctional photoprobes Part 4. Synthesis of the chromoge-nic, cleavable, water soluble and heterobifunctional (N-Methyl amino perfluoroaryl azide benzamido)-ethyl-l,3-dithiopropionyl sulfosuccinimide An efficient protein cross-linking agent. Bioorg. Chem. 26(4), 201-212. 

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