Synthesis of polyamino nitriles, en route to acylpolyamine neurotoxins, via the regioselective michael cyanoethylation of unprotected polyamines. Unusual behaviour of 1-(2-aminoethyl)piperazine

The Michael cyanoethylation of 1-(2-aminoethyl)piperazine, 4,4′-methylenebis(cyclohexylamine) and bis(3-aminopropylamine)amine, leading to acrylonitrile free (<100 ppm) polyamino nitriles, as a key step in the synthesis of higher polyamines useful in the synthesis of acylpolyamine neurotoxins, was carried out regioselectively on a multigram scale by careful tuning of reaction conditions, without a necessity to protect nitrogen atoms. The higher reactivity of primary amino groups in aliphatic diamines and triamines [as in bis(3-aminopropylamine)amine] was also observed in the cyclic amine, 4,4′-methylenebis(cyclohexylamine), but reversed in 1-(2-aminoethyl)piperazine. The compounds with a dicyanoethylated nitrogen atom were thermally less stable than the monocyanoethylated ones.