Glucuronic acid, also known as glucuronic acid, is a uronic acid formed when the C-6 hydroxyl group of glucose is oxidized to a carboxyl group. D-glucuronic acid generally does not exist in the free form because this form is unstable, but in the more stable 3,6-lactone form of the furan ring. D-glucopyranuronic acid is found in oligosaccharides at the junctions of glycosaminoglycan chains and also in heparin and chondroitin.