Which among the following is not naturally occurring estrogen?

Estrone, Estradiol and Estriol are natural estrogens The biologically active estrogen is estradiol Estrone and estriol are weaker estrogens Adipose tissue and liver conve androstenedione into estrone Diethylstilbesterol is a synthetic, non-steroidal estrogen of the stilbestrol group. DES is known to cause clear cell carcinoma, a rare vaginal tumor in girls and women who had been exposed to this drug in utero. Ref: Shaw's Textbook of Gynaecology, 15th edition, page no: 309