Preparation of hexaaza and heptaaza macrocycles functionalized with a single aminoalkyl pendant arm

Abstract

A practical and reproducible route for the preparation of 1,4,7,10,13,16,19-heptaazacyclohenicosane (1), 1,4,7,10,13,16-hexaazacyclooctadecane (2), and 1,4,7,10,13,17-hexaazacycloicosane (3) bearing a single N-(2-aminoethyl) pendant arm has been developed. Richman–Atkins cyclization in the presence of caesium carbonate was applied to construct the macrocycle from 3-benzoyl-N¹,N⁵-ditosyl-3-azapentane-1,5-diamine and the appropriate fully N-tosylated N^α,N^ω-bis(2-mesyloxyethyl) tri- or tetra-amine. The benzoyl group was selectively removed with potassium tert-butoxide, and the exposed nitrogen atom was reacted with N-tosylaziridine. The tosyl protections were removed with hydrogen bromide in acetic acid, and the product was converted to a free base with the aid of a strong anion exchange resin (OH⁻ form).