Asymmetric Aza-Henry reaction

A recent paper on JACS,2007,129,12392-12393. Which is a smart work in developing a Tetraaminophosphonium salt based chiral ligand.

The ligand synthesis began with treatement of Diamine with PCl5, to form the phosponium catalysts. My question is what will be if we use a aminoacid in place of the diamine, there are no reports Aminoacids based phosphonium salt. Iam not sure about the sterically bulcky groups which dictates the enentioselectivity in this particular paper, imean if i used a simple L-Valine in palce of the of the L-Valine derivative (Which is used in the current paper). I dont know why the author choose L-valine derivative insted of a simple L-Valine.

Iam working on catalyst developement for Aza-Henry reaction especially on cyclic imines.

But a good paper to read.

Ahamed.