Reaction Steps
A solution of [3aR-[3aα,5α(2R*,3S*),6α,6aα]]-2-(Tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol (V) (0.5 g, 2.0 mmol) in trifluoroacetic-water (9:1) (25 mL) was stirred, under nitrogen, at ambient temperature for 20 h. The purple solution was then concentrated in vacuo (40° C.) leaving a thick syrup which was dissolved in deionized water (25 mL). This solution was basified to a pH of about 9.0 by the addition of 1N aqueous sodium hydroxide (5.5 mL) and hydrogenated at 3.4 atmospheres over 5% Pt on carbon (0.3 g) on a Parr apparatus for 16 h. The mixture was filtered through a celite pad and the collected catalyst washed with water (2×20 mL). The combined filtrate was adsorbed on a column of Dowex 50 W-X8 (H+) ion exchange resin (10 mL) (prewashed with 200 mL of water) and eluted first with deionized water (200 mL) and then with 1N ammonium hydroxide solution (twenty×20 mL fractions were collected). (+)-Castanospermine (VI), 0.23 g (61%) was obtained from fractions 1-15. An analytical sample was obtained as colorless prisms by recrystallization from 90% ethanol: mp 210°-212° C. dec. [lit. 212°-215° C. dec]; [α]D25 =81.4° (c 1.0, H2O) [lit. [α]D25 =+79.7° (C 0.93, H2O)]; 1H NMR (D2O) δ 4.42 (ddd, 1, J=7.0, 4.5, 2.1Hz, H-1), 3.62 (ddd, 1, J=10.6, 9.4, 5.1 Hz, H-6), 3.60 (dd, 1, J=9.8, 9.0 Hz, H-8), 3.32 (dd, 1, J=9.8, 9.0 Hz, H-7) 3.18 (dd, 1, J=10.8, 5.1 Hz, H-5), 3.08 (ddd, 1, J=9.0, 8.8, 8.8 Hz, H-3), 2.34 (dddd, 1, J=13.9, 9.0, 7.0, 2.2 Hz, H-2), 2.22 (ddd, 1, J=9.3, 9.0, 8.8 Hz, H-3'), 2.06 (dd, 1, J=10.8, 10.6 Hz, H-5'), 2.02 (dd, 1, J=9.8, 4.5Hz, H-8a), 1.71(dddd, 1, J=13.9, 9.3, 8.8, 2.1 Hz, H-2'); 13C NMR (D2O) δ 35.6, 54.5, 58.3, 71.9, 72.5, 73.0, 74.3, 81.9; mass spectrum, m/z(rel intensity) 190 (MH+, 50), 172 (MH+ -H2O, 100).
