Schiff base derived boron

In the covalent approach (Figure 2), a polymerizable derivative of the template is obtained by linking the template with a vinyl functional monomer via a strong reversible covalent bond (e.g., boronate esters, Schiff bases, or ketal). The derivatized print molecule is then radical copolymerized with an excess amount of a cross-linking agent, using either thermal or photochemical radical initiation. Reaction conditions are... 

Schiff base 1 with 5-iodo-2-methoxybenzyl bromide and CsOH H2O under the influence of PTC 1 and subsequent acid hydrolysis provided the amino acid hydrochloride 18 in 86% yield with 96% ee. Similar to Lepine and Zhu s strategy, the synthesis diverged at this point, and two substituted phenylalanine derivatives 19 and 20 were prepared. Then, the boronate 19 and the free iode acid 20 were coupled to give the biaryl acid 21 without epimerization. After derivatization of 21 to dipeptide 22, ring closure to the macrolactam 23 was achieved using HATU/HOAt" under the pseudo—high-dUution condition. Deprotection of all the functional groups and reduction of the azide moiety furnished 11. 

---