Synthesis of carboxy-polyethylene glycol-amine (CA (PEG)n ) and [1-14 C]-CA (PEG)n via oxa-Michael addition of amino-polyethylene glycols to propiolates vs to acrylates.

Synthesis of carboxy-polyethylene glycol-amine (CA (PEG)n ) via oxa-Michael addition of amino-polyethylene glycols to either acrylates or propiolates was investigated. Compared with the oxa-Michael addition to acrylates, the corresponding addition to propiolates was found to proceed under mild reaction conditions and afford the adducts in high yields from a broad scope of substrates. A two-step efficient and convenient synthesis of benzyl [1-14 C]-propiolate from 14 CO2 was therefore developed and utilized as a common synthon to afford practical and high yielding access to [1-14 C]-CA (PEG)n .