Two methods for the resolution of 10,10'-dihydroxy-9,9'-biphenanthryl were developed. The first involved salt formation with (-)-strychnine via its cyclic diester with phosphoric acid. The second method involved the formation of diastereomers (R)- and (S)-9,9'-biphenanthryl-10,10'-diyl N-((-)-alpha-methylbenzyl)phosphoroamidates. (C) 1998 Elsevier Science Ltd. All rights reserved.