Synthesis of CD-ring modified 1-alpha,25-dihydroxy vitamin D analogues: Five-membered D-ring analogues Yong, W.; Ling, S.; D'halleweyn, C.; Van-Haver, D.; De-Clercq, P.; Vandewalle, M. Bioorganic and Medicinal Chemistry Letters 7(7): 923-928 1997 https://eurekamag.com/research/009/507/009507472.php