Russian-born American chemist and pioneer in the study of nucleic acids (nucleic acid).

On receiving his M.D. degree from the St. Petersburg Imperial Medical Academy in 1891, Levene fled from Russian anti-Semitism and settled in New York City. While practicing medicine there, he studied chemistry at Columbia University and ultimately decided to devote his life to chemical research. From 1905 to 1939 he worked at the Rockefeller Institute for Medical Research.

Although Levene's studies encompassed nearly every major class of organic compounds, his most valuable work was on the nucleic acids. He isolated the nucleotides, the basic building blocks of the nucleic acid molecule; and in 1909 he isolated the five-carbon sugar d-ribose from the ribonucleic acid (RNA) molecule. Twenty years later he discovered 2-deoxyribose (a sugar derived from d-ribose by removing an oxygen atom), which is part of the deoxyribonucleic acid (DNA) molecule. He also determined how the nucleic acid components combine to form the nucleotides and how the nucleotides combine in chains. Although the importance of the nucleic acids was unrecognized when he began his research, later discoveries showed DNA and RNA to be key elements in the maintenance of life.