Scheme 1a.

^aReagents and conditions: (a) MeOH, H⁺-resin, >99%; (b) Ac₂O, pyridine, DMAP, 95%; (c) HCl, AcOH/Ac₂O, >99%; (d) AllOH, silver salicylate, MS (4Å), 93%; (e) 1N NaOMe, MeOH, 93%; (f) 4N Me₄NOH, MeOH/H₂O, 78%; (g) Pr₂O or iBu₂O, H₂O (pH 10), 83-85%; (h) PhAcCl, MeOH, 75%; (i) CF₃CH₂COOBt, DMF, 55%; (j) 1.0N NaOH, H₂O, rt, 95%; (k) O₃, MeOH; then Me₂S, 80-90%; (l) NaBH₃CN, KLH, buffer (pH 7.5); (m) NaBH₃CN, HSA, buffer (pH 7.5).