Condensation in equimolar amount of o-carboxybenzaldehyde with primary amines, such cyclohexyl and iso-propyl, yields oily products which by subsequent addition of dimethylphosphite produce in very good yield amido-amino-phosphonic acid mono-methyl esters, very soluble in water and in protic organic solvents. The by-product of this addition reaction is a cyclic amino-phosphonic acid dimethyl ester. Characterization of these new compounds is made by NMR spectroscopy (H-1 and P-31), by MS-FAB techniques and IR spectroscopy. A possible reaction mechanism leading to these unexpected products is outlined. Although the phosphorylation reaction is quite complex on the molecular level, this procedure allows to obtained in a very convenient way and by one-pot reaction good yields of aminophosphonic acid mono-methyl esters containing ancillary moieties (the amido group) suitable for complexing metals. Furthermore, in an extended way, the compounds obtained can be thought of as the non-natural analogs of peptides and therefore they can be of utility in biological tests.