Protonated amino-olefin complexes

Complexes with this formulation satisfy the generally accepted criteria for structural features required in an antitumor-active platinum complex, but are expected to possess kinetic advantages when compared to the prototype antitumor platinum complex, cis-dichloro-diamineplatinum (II). Complexes have been prepared where L is a monoprotonated diamine and also where L is a protonated amino-olefin. All complexes have been examined for cytotoxicity against L1210 leukemia in cell culture, and selected compounds have been tested for antitumor activity vivo (LI210 leukemia in BDF mice). One compound, where L is protonated 3-amino-quinuclidine, has significant vivo activity, with T/C approaching 150%. 

In the absence of protonation, the neutral amino-olefin is, in principle, capable of coordination as a chelate ligand, utilz-ing both the olefin ir-system and the nitrogen lone pair. This would produce a neutral complex of type V, which should also be activated toward the substitution reaction of equation (1), and. 

Inspired by this finding, Katuski further developed a series of structurally tunable di- x-oxo titanium-salan complexes that can be easily prepared and possess amino protons to activate a putative peroxide species. The optimized catalyst (5 mol%) works well for the epoxidation of a variety of unfunctionalized olefins, giving the corresponding epoxides in moderate to good yields with 55-97% ee [262]. The ready availability of the salan ligand and aqueous H2O2 oxidant makes the process very practical for the production of optically active epoxides. 

Apart from aminolysis and olefin metathesis the photoactivation of aminocar-bene complexes offers another nonconventional entry into peptide synthesis. Irradiation into the hypsochromic MLCT-band of chromium aminocarbenes such as 201 generates a ketene-like intermediate 204 that is trapped by amino acid esters such as 202 or 205 to produce dipeptides 203 or 206 after enantioselective protonation (Scheme 11.49) [106]. This photochemical protocol generally combines good yields with high diastereoselectivities and is especially attractive for the incorporation of a-alkyl a-amino acid esters into peptides that may be hampered in conventional peptide synthesis methodologies due to steric hindrance [106c]. 

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