Novel solid-phase synthesis of thiol-terminated-poly(alpha-amino acid)-drug conjugate.

A new method using a controlled pore glass solid support for the preparation of a thiol-terminated-polymerdrug, notably poly-L-glutamate-daunomycin having a terminal thiol group, is described. The method consists of first polymerizing an ester-protected glutamic acid onto an amino-disulfide functionalized controlled pore glass support. The ester protecting group is then removed, freeing the gamma-carboxyl groups of the grafted polymer which then allows it to react with daunomycin. Finally, the disulfide bond linking the conjugated polymer-drug to the solid support is broken by thiolysis, thus releasing the desired product. The final product consists of only polymer-drug conjugates with terminal thiol groups (global yield 26%). This novel method is much simpler and more elegant than more conventional preparation methods requiring solution phase techniques.