Amine donors

In nature, aminotransferases participate in a number of metabolic pathways [4[. They catalyze the transfer of an amino group originating from an amino acid donor to a 2-ketoacid acceptor by a simple mechanism. First, an amino group from the donor is transferred to the cofactor pyridoxal phosphate with formation of a 2-keto add and an enzyme-bound pyridoxamine phosphate intermediate. Second, this intermediate transfers the amino group to the 2-keto add acceptor. The readion is reversible, shows ping-pong kinetics, and has been used industrially in the production ofamino acids [69]. It can be driven in one direction by the appropriate choice of conditions (e.g. substrate concentration). Some of the aminotransferases accept simple amines instead of amino acids as amine donors, and highly enantioselective cases have been reported [70]. 

However, this is obviously not always the case, a counter example being the transformation of P-tetralone (23) to (S)—anunotetralin (24), with 2-amino butane serving as the amine donor. The of an (S)-selective aminotransaminase leads to a value of only... 

Electron density is transferred from a Lewis donor to a Lewis acceptor, here shown for an amine (donor) interacting with a phosphenium cation (acceptor). The lone pair orbital at the amine dives into the emptyp-orbital of the phosphenium cation, hollowing the ideas of Mulliken the donation towards an acceptor can be viewed as sketched in Scheme 2. 

When Ni(0Ac)2 4H20 is employed, a dimeric complex (551) with a coordinated Schiff base forms, because the amine donor reacts with the solvent acetone. With Ni(C104)2 6H20, a trinuclear complex (552) is obtained which is readily oxidized upon exposure to air or by aqueous... 

Bulk electrochemical reduction of the platinum(IV) complex of the tridentate ligand l,l,l-tris(aminomethyl)ethane(tame), [Pt(tame)2]4+, leads to the quantitative formation of [Pt(tame)2]2+ (28), in which one of the amine donor groups in tame remains noncoordinated.141 The X-ray structure of the diprotonated complex [Pt(Htame)2]4+, as its tetrachlorozincate(II) salt, is also reported. 

Inspired by the results of aromatic-ring hydroxylation from the laboratory of Karlin and co-workers, a few groups provided further examples of such reactivity, including some structurally characterized complexes of modified m-xylyl-based pyridine-donor ligands (Schiff base and non-Schiff base acyclic ligands), as well as aliphatic amine donor ligands (179) (Cu-Cu 2.990 A),169 (180) (Cu-Cu 3.015 A),170 and (181) (Cu-Cu 2.999 A).171 172 A m-xylyl-based ligand system that was used by Mukherjee and co-workers in the formation of complex (181) also resulted in the isolation of a bis(/i-hydroxo)dicopper(II) complex (182) (Cu-Cu 3.004 A).171,172 Casella and co-workers demonstrated that when their dicopper(I) complex... 

Copper(l) analogues [(L)Cu(MeCN)][CF3S03] (747) [yellow, four-coordinate (two amine donors, one of the two pyridinyl groups and an MeCN] and [(L)Cu(MeCN)][BF4] (748) [red, five-coordinate (two tertiary amine, two pyridinyl and an MeCN] [L as that in copper(II) complex (241)] were structurally characterized and redox properties of these complexes were also investigated.224... 

This time using hydrazine hydrate as the amine donor, reaction with l,3,4-oxadiazole-2-(3//)-thiones 223a-e under heating in ethanol yielded the corresponding l,2,4-triazole-2-(3//)thiones 224a-e (Equation 69 and Table 46) <2005EJM1156>. 

It is well-established that the molecular and electronic structures of metal complexes of azamacrocycles are greatly affected upon N-alkylation (197). This is mainly due to two factors (a) the decrease of the ligand field strength and (b) the increase in the steric requirements upon going from a secondary to a tertiary amine donor function (251). To examine whether the properties of the dinuclear amine-thiophenolate complexes are affected by the N-alkyl substituents, analogous complexes of the... 

The conversion of the six secondary into tertiary amine donor functions does not change the overall structure of the [M2(Lr)( -L )]+ complexes. That is the complexes retain their bioctahedral N3M( -SR)2( -L )MN3 core structures and the macrocycle conformation remains constant for a given coligand, see for instance the isostructural compounds 52-55 (211). This offers the opportunity to extend the rims of the binding pocket of the [M2(LR)(L )] complexes. 

The complexes can be classified into two general types. Those involving neutral hydroxy and amine donor sites include complexes of Bi3+ with the multidentate, formally neutral ligands cyclenOH and... 

The direct photocyclization of another interesting acceptor-donor pair, the amine-enone system, has been reported by Mariano [224-226]. Direct irradiation of -(aminoethyl)cyclohexenones 281 leads to the excitation of the conjugated cyclohexenone chromophore. Intramolecular single-electron transfer from the amine donor to the cyclohexenone excited state results in the formation... 

Solution studies involving a tetracarboxymethyl pendant arm derivative of an 18-membered, Ng donor macrocycle incorporating two pyridyl and four tertiary amine donors demonstrated that this ligand coordinates well to a wide variety of metal ions (including manganese) in various oxidation states. In part, this coordination versatility was attributed to the flexibility of the ligand framework allowing it to accommodate readily the coordination sphere preferences of the respective metals in relation to both their oxidation states and their ionic radii. 

The vast majority of amino acid dehydrogenases use ammonium ions as the amine donor. However, recently a novel N-methyl-L-amino acid dehydrogenase (NMAADH), from Pseudomonas putida, was isolated and used to synthesize N-methyl-L-phenylalanine 36 from phenylpyruvic acid 31 and methylamine 35 in 98% yield and greater than 99%e.e. (Scheme 2.15). The enzyme was shown to accept a number of different ketoacids and also use various amine donors. Glucose dehydrogenase from Bacillus suhtilis was used to recycle the NADPH cofactor [17]. 

From a practical viewpoint they suffer from serious product inhibition and/or equilibrium constraints. One way of avoiding the latter issue is to couple the transamination step to a second enzymatic step which removes the coproduct In the example shown in Scheme 6.16 acetophenone undergoes TA-catalyzed transamination using L-alanine as the amine donor. The unfavorable equilibrium and... 

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