Synthesis of a water soluble boron neutron capture therapy agent: 1-amino-3-[2-(7-{3-[2-(2-hydroxymethyl-ethoxy)-1-(2-hydroxy-1-hydroxymethyl-ethoxymethyl)ethoxy]propyl}-1,7-di-carba-closo-dodecaboran-1-yl)ethyl]cyclobutanecarboxylic acid

A water soluble boronated amino acid containing a cascade polyol, 1-amino-3 -[2-(7-{3-[2-(2-hydroxymethyl-ethoxy)-1-(2-hydroxy-1-hydroxymethyl-ethoxyme thyl)ethoxy]propyl}-1,7-di-carba-closo-dodecarboran-1-yl)ethyl]cyclobutanec arboxylic acid,has been developed. The key step in the synthesis is the alk ylation of 3-[2-(1,7-dicarba-closo-docfecarboran-1-yl)ethyl]cyclobutanone h emithioketal with toluene-4-sulfonic acid 3-[2-(2-benzyloxy-1-benzyloxymeth yl-ethoxy)-1-(2-benzyloxy-1-benzyloxymethyl-ethoxymethyl)ethoxy]propyl este r which gave the required precursor ketone which was then converted to the title amino acid via a Bucherer-Strecker synthesis followed by hydrogenolys is to remove the benzyl protecting groups. (C) 2000 Elsevier Science B.V. A ll rights reserved.