A portion of the NBF was applied onto a
water-cooled glass column (25 1 cm i.d.) (12 C) filled with
slurry of purified silica gel (8 g). Elution was performed with pentane
(50 mL), followed by pentane/diethyl ether (9:1; v/v, 50 mL),
pentane/diethyl ether (7:3; v/v, 50 mL), and finally diethyl ether
(50 mL).