ELSEVIER Synthesis of novel 214rifluoropregnane steroids: Inhibitors of 17~ hydroxylase/l7,20=lyase (lircu-lyase) Vincent C.O. Njar, Gregory T. Klus, Hausa H. Johnson, and Angela M.H. Brodie Department of Pharmacology and Experimental Therapeutics, School of M edicine, University of M aryland, Baltimore, M aryland, USA Novel 21-trifluoropregnenolone (6), 21-trifluoroprogesterone (7) and related compounds 4a and 8 have been sy nthesized in high y ields from 3B- acetoxy androst- 5- ene- I 7fl- carbaldehy de (3). The key reaction was the conversion of 3 into the 21-trifluoromethyl-20-alcohol as a diastereomeric mixture (4) by trifluoromethyltri- methy lsilane (TM % CF,) in the presence of tetrabutylammonium fluoride (TBAF). All compounds, including 4 and 7, were unambiguously characterized by IR, ‘Hand 19F NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. On this basis, we concluded that the only report of an earlier synthesis of 6 and 713 is erroneous. Enzyme inhibition studies showed that 20 [-hydroxy-21-trifluoropregn-4-en-3-one (8) is a potent inhibitor (IC,, value = 0.6 ~.LM) of rat 17~hydroxylase/l7,20-lyase. (Steroids 62:468-473, 1997) 0 1997 by Elsevier Science Inc. Keywords: synthesis; inhibitor of 17~hydroxylase/l7,20-lyase Introduction 17a-Hydroxylase/l7,20-lyase (17a-lyase or CYP 17) is a cytochrome P-450 enzyme complex that catalyzes the con- version of progesterone and pregnenolone into androgens.‘,* The potential therapeutic value of 17a-lyase inhibitors in the treatment of androgen-dependent diseases, for example, prostate cancer, has led to much recent interest by our group and others.3-8 Our group has previously reported536 that simple deriva- tives of progesterone and pregnenolone are potent inhibitors of 17cy-lyase. While Petrow and Lack9 reported that proges- terone itself is also a strong inhibitor of this enzyme, its rapid metabolism in vivo detracts from its value as a ther- apeutic agent. In addition, it is well established that intro- duction of fluorine into various positions of certain steroid hormones (fluorosteroids) has often yielded useful thera- peutic agents.‘O-‘* Perhaps more relevant to this work are recent reports that various fluoro ketones are potent inhib- itors of hydrolytic enzymes such as acetyl cholinesterase” or juvenile hormone esterase.14 Consequently, we embarked on the synthesis of the here- tofore undescribed (vide infra) 2 1-trifluoropregnane ste- roids 4b, 6,7, and 8 (Scheme 1) on the basis that they may bind tightly to the 17a-lyase enzyme, resulting in its inhi- bition. We also considered the possibility that compounds 6 and 7 might each be processed by the enzyme to form trifluoroacetate anion as one of the products. The latter might react covalently at the active site of the enzyme, resulting in irreversible inhibition. At the commencement of this study, a literature survey revealed one report of a synthesis of 21-trifluoropreg- nenolone (6) and 21-trifluoroprogesterone (7),i5 which in- volved the use of perchloryl fluoride as the fluorinating agent. However, we envisioned an attractive, alternative, simple procedure that would produce a trifluoromethyl carbinol (4) and subsequently oxidize this intermediate to the corresponding ketone. Our strategy was successful, and we have unambiguous evidence to show (vide infra) that the only reported procedure I5 on the synthesis of the 21- trifluoro compounds 6 and 7 is erroneous. We note that the corresponding 2 1-mono- and 2 1 -difluoropregnane steroids have been synthesized since 1959,i63i7 and new synthetic methods have also been developed.ls-*l In this paper, we describe the synthesis of novel 21-trifluoropregnane ste- roids (4a, 6-8) and includes some preliminary data on their 17a-lyase inhibitory activity. Dr. Vincent C. 0. Njar is on leave from Department of Chemistry, University of Ibadan, Ibadan, Nigeria. Address reprint requests to Dr. Angela M. H. Brodie, Department of Pharmacology and Experimental Pharmaceutics, School of Medicine, Uni- versity of Maryland, Baltimore, MD 21201, USA. Received October 7, 1996; accepted January 13, 1997. Steroids 62:468-473, 1997 0 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010 Experimental General methods Melting points (mp) were determined with a Fischer-Johns melting-point apparatus and are uncorrected. Infrared (IR) spectra 0039-128W97/$17.00 PII SOO39-128X(97)00016-0