tert-Butyl 3-Hydroxypropanoate is used as a reagent in the synthesis of 5-aminolevulinic acid derivatives which in turn can be used as photosensitizing agents in photodynamic treatment and diagnosis. tert-Butyl 3-Hydroxypropanoate is also used as a reagent in the preparation of pyrrolidinylcarboxamide derivatives for use as antitumor agents.