 A derivative of hypoxanthine was subsequently shown by others to be the key product of purine biosynthesis.Krebs became Edson's lifelong friend, a long-range source of scientific advice, a host for his future postgraduate students and his own sabbatical in 1956 (see Krebs, 1981).Edson also befriended Luis Federico Leloir to whom he dedicated his 1966 paper on glucogenesis from sorbitol to celebrate Leloir's 60th birthday.