Patent ID: 7122662

Claim:
A compound represented by formula (Ik) or its salt wherein P 1 and P 2 independently represent hydrogen atom or a protective group selected from the group consisting of aralkyl groups, acyl groups and alkoxycarbonyl groups; Y is an oxygen atom, —S(O) y —, or an optionally substituted imino group (—NH—); Z is a methylene group, carbonyl group or thiocarbonyl group; l, m, n, and y are independently an integer of 0, 1 or 2, with the proviso that l and m are not simultaneously 0; D is hydrogen atom, —CO—R 5 (wherein R 5 is hydrogen atom or a substituent), or an optionally substituted C 1-6 alkyl group; r is an integer of 0 or 1; and the three rings are independently optionally substituted.