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Synthesis of 30-diethoxyphosphoryloxybetulin 5 and its alkynyl derivatives 6a–6e and 7a–7e. Reaction conditions: (i) (CH3CO)2O, pyridine, room temp.; (ii) m-CPBA, CHCl3, reaction at boiling temp.; (iii) (C2H5O)2P(O)Cl, DMAP, pyridine, room temp.; (iv) NaOH, THF/MeOH/H2O, room temp.; (v) for A—DCC, DMAP, CH2Cl2, from −10 to room temperature, for B—pyridine, benzene, from −5 to room temp.
