Hydrazino ligand

The high electrophilicity of the positively charged element can be modified by intramolecular donation from remote donor substituents. This interaction leads to solvent-free cations with coordination numbers for the positively charged element > 3 and to a considerable electron transfer from the donor group to the element. Frequently used donor substituents utilize heteroatoms with lone pairs (e.g. amino, hydrazino, methoxy, carboxy, phosphino, etc.), in many cases in combination with pincer-type topology of the ligand, for the stabilization of the cationic center. These strongly stabilized cations are beyond the scope of this review and instead we will concentrate on few examples where we have weak donors such as CC multiple bonds, which stabilize the electron-deficient element atom. 

A hydroboration-oxidation sequence has been described for the desymmetrization of bicyclic hydrazino-alkenes. The use of BDPP as a chiral ligand on Rh provides the desired alcohol in 84% ee, following oxidation of the hydroborated... 

The ability of 2-aminothiazoline (128) to complex metal ions has been investigated 2-aminothiazoline does not form powerful coupling ligands with Ca, Mg, Mn, Ni, Cu, or Zn ions. The amino-group is the sole electron-donor that is involved in the complexing of 2-aminothiazoline. 2-Hydrazino-... 

Babich J W, Fischman A J (1995). Effect of co-ligand on the biodistribntion of Tc-labeled hydrazino nicotinic acid derivatized chemotactic peptides. Nucl. Med. Biol. 22 25-30. 

The IR spectra of Co(ll,lll) and Cu(ii) complexes of hydrazones obtained by the reaction of 5,6-diphenyl-3-hydrazino-l,2,4-triazine with furfural <2002TML398> and 2-acetylpyridine <2004JCR105> have been studied to determine the coordination sites of these ligands. In addition, Mn(ii), Ni(ii), and Cu(ll) complexes of hydrazones derived from 4-amino-3-mercapto-6-methyl-l,2,4-triazin-5(4//)-one were elucidated by IR spectra <2000SRI979>. 

Phthalimidomethyl-substituted 477-pyrido[4,3-( ]-l-thia-2,4-diazine 1,1-dioxide derivative 125 undergoes hydrazino-lysis to produce the (7-3-aminomethyl-substituted product, which is then acylated to yield the amido adducts 126 (R = H, Ph R =Ar, NHAr) as potential cholecystokinin/gastric receptor ligands (Equation 17) <1997BSB781>. Similar acylation chemistry has been applied to the synthesis of related 5-(methylamides) of 2/7-benzo-l-thia-2,4-diazine 1,1-dioxides (see Section 9.05.9.1.3) <2001CHE237>. 

The condensation of L48 and its derivatives with 2,6-dfp in the presence of aqueous chromium(III) chloride led to the formation of the metal-free macrocycles L735-L737 [133]. Reaction of the phenanthroline analogue, 2,9-bis(l-methyl-hydrazino)-l,10-phenanthroline, occurs in a similar way. In no case could a chromium(III)-containing complex of either initial or toal ligands be isolated from the reaction mixture. Identical yields of metal-free macrocycles were obtained when the reaction was conducted in the presence of chromium(lll) chloride, chromium(III) chloride and hydrochloric acid (pH 1), or hydrochloric acid alone. Only low yields of macrocycles were obtained in the absence of acid (pH = 6) or in acetate buffer. This indicates that the proton is the true template in these chromium-mediated reactions. 

Coupling of hydrazino-derivatized ligands to aldehyde functionalized liposomes by hydrazone formation (Fig. Ic) has been described by Bonnet et al. [20], who... 

The method described by Bonnet et al. [20] offers an effective approach to conjugate synthetic peptides prepared by solid-phase peptide synthesis (SPPS) to liposomes. The hydrazino functionality is easily introduced to the synthetic peptide on resin by the use of A, A A -tri(rert-butyloxycarbonyl)-hydrazino acetic acid, which is fuUy compatible with SPPS synthesis [18, 19]. Furthermore, hydrazone formation occurs spontaneously without the need of a catalyst. Thus, this method is one of the most effective for the functionalization of liposomes with targeting ligands when it is possible to introduce a hydrazino group into the ligand. However, this is unfortunately problematic for antibodies and other complex ligands. 

Figure 45.2 IC50 (50% cell proliferation inhibition concentrations) of the hydrazino-paullone (HP), ligand Lla, and its gallium complex [Ga(Lla-H)2]Cl on different cancer cell lines [54].

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