Studies on Monoterpene Glucosides and Related Natural Products. XV. Confirmation of the Absolute Configuration of Catalpol

Stereoselective Hydrogenation and Ozonolysis of Iridoids. Conversion into Carbocyclic Nucleoside Analogues

“…Thus, the present protection scheme was shown to be superior to alternate analogous hydrogenations. 21,22 To rule out that the above-observed selectivity was due to a steric effect exerted by the protected sugar moiety, both Pt-and Pd/C-catalyzed hydrogenations were performed on olefin 20. As expected, the 8R-epimer 23 was predominant when Pt was used (R:β ratio 10:1), while Pd/C catalysis in this case only afforded an R:β ratio of 1:3 (i.e., between 23 and 24).…”

“…The residue was purified on a VLC column (4 × 4 cm). Elution with hexane and then hexane-Me2CO (20:1 and 15:1) gave di-O-benzyl-triol 32 (0.78 g, 94%): [R] 22 Di-O-benzoyl-tetrol 33. Acetonide 29 (1.06 g, 4.60 mmol) was dissolved in CH2Cl2-pyridine (4:1, 15 mL), and then BzCl (1.34 mL, 11.5 mmol) was added.…”

“…The residue (0.65 g) was purified on a VLC column (3 × 3 cm). Elution with hexane and then hexane-Me2CO (10:1 and 9:1) yielded 34 (0.48 g, 85%) as a colorless syrup: [R] 22 Bisnucleoside Analogue 35. Acetonide 29 (144 mg, 0.625 mmol), Ph3P (656 mg, 2.50 mmol), and 6-chloropurine (387 mg, 2.50 mmol) in dry THF (7 mL) were cooled to 0 °C, when a solution of DEAD (0.38 mL, 2.45 mmol) in dry THF (3 mL) was added dropwise.…”