(2E,4Z,8Z,10E,14E,18E,20Z)-(6R,17S)-20-(2-Hydroxy-ethyl)-6-methoxy-2,5,17-trimethyl-docosa-2,4,8,10,14,18,20-heptaenedioic acid 1-tert-butyl ester 22-(tert-butyl-diphenyl-silanyloxymethyl) ester