Riboflavin

Scientists had found multiple water-soluble vitamins similar to the vitamin B that cured beriberi. The one that cured beriberi came to be known B-1, and it and its cousins were named the B-complex. Riboflavin, also known as vitamin B-2, was synthesized and its structure confirmed.
 Paul Karrer Switzerland 1935 Riboflavin

Scientists had found multiple water-soluble vitamins similar to the vitamin B that cured beriberi. The one that cured beriberi came to be known B-1, and it and its cousins were named the B-complex. Riboflavin, also known as vitamin B-2, was synthesized and its structure confirmed.