Scheme 2. Reagents and Conditions.

(a) H₂, Lindlar catalyst, EtOH, 4 h, quant. (b) Boc₂O, TEA, THF, 12 h, 86%. (c) NaOMe, MeOH, 1 h, quant. (d) H⁺ resin, acetone, 12 h, 88%. (e) DMAP, pyridine, p-NO₂C₆H₄OCOCl, 12 h, 80%. (f) 6-Azido-hex-1-amine, CH₃CN, TEA, 3 h, 89%. (g) TFA, DCM. (h) 1,3-Bis(tert-butoxycarbonyl)-2-methyl-2-thiopseudourea. HgCl₂, TEA, DCM, 12 h, 84%. (i) Na-L-ascorbate, CuSO₄, THF/H₂O, 12 h. 78% for 11a; 80% for 11b. (j) NaOH, MeOH. 1 h. 70% for SC7; 79% for SC8. (k) H₂, Lindlar catalyst, EtOH, 4 h. 76% for SC5; 72% for SC6.