Mesyloxycarboxylic acid

Although there is a number of syntheses of 14 [9] the main problem lies in the differentiability of the two amino functions, preferably in form of p-BOC and a-Fmoc-protection as shown in formula 16. Our synthesis (Fig. 11) proceeds via the P-azido-a-mesyloxycarboxylic acid 17, readily available from 6 by azide opening. Methylation and reduction of the azide function, followed by BOC protection, furnishes 19, which after a second 8 2 displacement reaction with azide gives 20. By ester hydrolysis, azide reduction and Fmoc-protection the desired bis-amino acid 16 is obtained in gram quantities. 

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