Clindamycin phosphate EP impurity K; Dilindamycin pyrophosphate; 2,2'-Oxybis(hydroxyphosphoryl)bis[methyl 7-chloro-6,7,8-trideoxy-6-[[[(2S,4R)-1-methyl-4-propylpyrrolidin-2-yl]carbonyl]amino]-1-thioxo-L-thio-L-threonine-α-D-galactopyranose-octapentapentapentapyrrole]