The Cytotoxic Activity of Bis(α-aryl-methylphosphonoyl)amines and Derivatives Obtained by the Tandem Kabachnik–Fields Reaction on Human Multiple Myeloma Cell Line U266

Background: α-Aminophosphonates, a representative class of phosphonates, are important due to their potential and real biological activity as pharmaceutical agents. The effect results from their enzyme-inhibitory properties. Objectives: We planned to complete the family of the earlier-prepared symmetric bis(α-aryl-methylphosphonoyl)amines and the unsymmetric variations derived from the Kabachnik–Fields reaction of α-amino-α-aryl-methylphosphonates, arylaldehydes, and diethyl phosphite, including four new derivatives in order to test them on human multiple myeloma cells U266. Methods: The new bis(P-functionalized methyl)amines were prepared by varying the reagents: using formaldehyde instead of the benzaldehyde derivatives, or applying dimethyl phosphite or diphenylphosphine oxide instead of diethyl phosphite in the Kabachnik–Fields reaction of α-amino-α-phenyl-methylphosphonate. The starting α-aminophosphonate was also reacted with formaldehyde and ethyl phenyl-H-phosphinate. Cell viability was assessed using the CellTiter-Glo assay after 72 h of treatment with the compounds at 10 and 100 µM. Computational analyses included logP prediction using SwissADME and target prediction using SwissTargetPrediction. Results: Except for one case, the members of the molecule library comprised (SS/RR and SR/RS diastereoisomeric mixtures, confirmed by detailed 1D and 2D NMR investigations. The members of the 11-member compound library were tested against human myeloma cells U266. It was found that, except for a few cases, the bis(P-functionalized) species affected cell viability only to a small extent. In three cases, the viability fell in the range of 60–70%. The symmetric product with two P(O)(OEt)2 functions and with two chlorophenyl rings exhibited an outstanding effect marked by a viability of 3%. The IC50 value of this compound was determined to be 72.67 ± 3.53 µM (95% CI: 60.59–80.18 µM). The greater activity was generally associated with the increased predicted lipophilicity. The in silico target analysis revealed a possible contribution of carbonic anhydrases to the cytotoxic effects. Conclusions: The pronounced cytotoxic activity on multiple myeloma cell line U266 may be related to the chlorophenyl substituents, which may increase lipophilicity and facilitate cellular uptake. Overall, both the aryl substitution pattern and the nature of the phosphorus-containing moieties appear to influence cytotoxic activity. The encouraging results justify further research in the field.