Compounds containing B–N bonds have shown interesting biological activity. One class of such molecules is the 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones (3a–j), which contain a B–N bond, have an α-amino acid moiety in the heterocycle, and have an exocyclic moiety related to an amino acid. The purpose of this work was to determine the inhibitory effects of 3a–j on the proliferation of murine L5178Y lymphoma cells. A new five-membered heterocyclic nucleus with apoptotic activity was found. The target products showed potent cytotoxicity in the L5178Y cell line. Among them, 3a exhibited the highest antineoplastic activity in L5178Y cells with an IC50 value of 22.5 ± 0.2 μM.