ON THE METHANOLYSIS OF KBBL, AN IMMUNOSTIMULANT DERIVED FROM ASCORBIC-ACID

Treatment of the immunostimulant KBBL (1a) in dry methanol with Amberlyst(R) 15 as catalyst yielded the epimeric spiro ketals 4a and 4b along with a minor amount of the pyranoid ketal 2. Contrary to a literature report, treatment of KBBL in 2% methanolic HCI gave the rearranged methyl ester 3 rather than ketal 2. Ketals 2, 4a, and 4b are potentially useful intermediates for the further elaboration of the ascorbic acid nucleus of KBBL because the ketone and one hydroxyl of the butyrolactone nucleus (derived from ascorbic acid) are simultaneously protected as an internal ketal. X-Ray structures of these compounds were obtained, contributing to our knowledge of the structure of the KBBL family of immunostimulants.