Nitrogen-Activating Group Effects

Table V. Effect of hydrophilic nitrogen on activity. groups in side chain at basic...

Besides activating the ring for substitution reactions, the A-oxide moiety can serve as an effective nitrogen-protecting group. For example, in order to suppress the product of N-N bond formation (Equation 11) in favor of the desired C l reaction product 32, azide 31 was prepared from A-oxide 29 in two steps (Scheme 4) <2002TL6035>. 

The activation effect was really observed in random screening of chiral ligand/ activator combinations. Enantioselectivity of the reaction is also increased by matched eombination of diol ligands and nitrogen activators. The replacement of 3- and 3 -positions with bulky phenyl groups, 3,3 -diphenyl-l,l -bi-2-naphthol (L ), may further prevent the aggregation of binolato-Zn and increase the enantioselectivity, because of their steric demand to provide (S)-l-phenylpropanol in up to 65% ee and quantitative yields. 

Since the adenine moiety is bound with its NH2 group pointing out from the protein and with N-1 pointing into the hydrophobic pocket, substitutions at these two nitrogens have different effects (21S). The N -hydroxyethyl-substituted analog is almost as active as NAD whereas the corresponding N-1 substituted analog possesses lower enzymic activity. 

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