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

Treatment of the immunostimulant KBBL (1a) in dry methanol with Amberl yst(R) 15 as catalyst yielded the epimeric spiro ketals 4a and 4b alon g with a minor amount of the pyranoid ketal 2. Contrary to a literatur e report, treatment of KBBL in 2% methanolic HCI gave the rearranged m ethyl ester 3 rather than ketal 2. Ketals 2, 4a, and 4b are potentiall y useful intermediates for the further elaboration of the ascorbic aci d nucleus of KBBL because the ketone and one hydroxyl of the butyrolac tone nucleus (derived from ascorbic acid) are simultaneously protected as an internal ketal. X-Ray structures of these compounds were obtain ed, contributing to our knowledge of the structure of the KBBL family of immunostimulants.