Phenylboronic acid is a compound with significant therapeutic potential, particularly in the context of cancer treatment. The analyzed literature highlights its positive characteristics and potential application as a pharmaceutical agent in cancer therapy. One of the key challenges in cancer therapy is minimizing its harmful effects on healthy cells and organs. In this context, the focus of this work is the investigation of the synthesis of conjugates of phenylboronic and cinnamic acid, a biologically active natural organic acid. The synthesis was conducted using a protocol common for the formation of amide bonds, which involves the activation of a carboxylic acid with N,N-dialkylcarbodiimide, with several modifications to the reaction conditions (reaction medium composition, carbodiimide used, temperature, etc.) in search of the most efficient synthetic procedure for obtaining derivatives of aminophenylboronic acid. Although it was not possible to isolate the pure desired conjugate after the syntheses, this paper provides a comprehensive review of the synthesis methods and purification of the raw products used. Ultimately, it was shown that even a mixture of cinnamic acid anhydride and its conjugate with aminophenylboronic acid exhibits significant cytotoxicity, and thus exceptional potential for further development of this type of antitumor drugs. Therefore, this work will undoubtedly serve as a foundation for the development of new synthetic approaches to obtaining conjugates of phenylboronic acid and naturally biologically active organic acids.