[CH2:1]1CCC(N=C=NC2CCCCC2)C[CH2:2]1.[C:16]([O:20][C:21]([NH:23][CH2:24][P:25]([CH2:28][NH:29][C:30]([O:32][C:33]([CH3:36])([CH3:35])[CH3:34])=[O:31])(=[O:27])[OH:26])=[O:22])([CH3:19])([CH3:18])[CH3:17].C(O)C>C1COCC1>[C:16]([O:20][C:21]([NH:23][CH2:24][P:25]([CH2:28][NH:29][C:30]([O:32][C:33]([CH3:36])([CH3:35])[CH3:34])=[O:31])(=[O:26])[O:27][CH2:1][CH3:2])=[O:22])([CH3:19])([CH3:18])[CH3:17]DCC (190 mg, 0.92 mmol) in THF (4 ml) is added dropwise in the course of 4 minutes to a solution of the phosphinic acid 1 (270 mg, 0.83 mmol) in dry THF (4 ml) and abs. ethanol (0.30 ml, 5.15 mmol) which is boiling under reflux. After 1.5 hours (checking by TLC), the reaction solution is cooled to room temperature and filtered. The filter residue is washed with ether. The filtrate is extracted with water (2×20 ml). The organic phase is dried over Na2SO4 and concentrated under reduced pressure. After purification by column chromatography on silica gel (ethyl acetate/heptane=3:2), the phosphinic acid ester 3 (100 mg, 34% of theory) is obtained. M.p. 117.5°-120° C.
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