Confirmation of the C-17 Stereochemistry of Pentolame by Single Crystal X-ray Analysis of its Monohydrate

The molecular and crystal structure of Pentolame, a 17β-aminoestrogen (17β-(5'-hydroxy-1'-pentylamino)-1,3,5(10)-estratrien-3-ol), has been determined by single crystal X-ray diffraction as its monohydrate. The structure was used to determine the absolute configuration of the newly formed stereogenic centre (C17), which could not be established unambiguously by NMR spectroscopy. This study confirms the absolute configuration as 17S by internal reference with the starting material, estrone [(8R,9S,13S,14S)-3-Hydroxyestra-1,3,5(10)-trien-17-one]. Pentolame monohydrate crystallizes in the triclinic system, space group P 1 with Z = 1. The B ring adopts the typical conformation of a distorted 7α,8β-half-chair. In crystal packing, the water molecule plays an essential role joining adjacent infinite chains, made up by head to tail hydrogen bonded steroid molecules.