Conformational analysis of 2-[bis-(2-chloroethyl) amino]-2-trans-tetramethylene-1, 3, 2-dioxa- and oxazaphosphorinanes 5–8, cyclophosphamide-type anticancer drugs, show that diastereometric six-membered ring 1, 3, 2-dioxaphosphor-inanes can adopt either a chair conformation with bis-(2-chloroethyl) amino mustard group equatorial (5) or twist-boat conformation with the bis-(2-chloroethyl) amino group pseudoequatorial (6). An X-ray ...