en moieties or atoms, where RPR independently is ???H, a protecting group or both RPR together are a protecting group and A8 is C1-8 alkyl, C1-8 alkenyl, C1-8 alkynyl, C1-6 alkyl-C2-9 aryl (e.g., benzyl), aryl (e.g. phenyl) or C0-6 alkyl-C1-7 heterocycle.