| 摘要 |
PCT No. PCT/GB96/02820 Sec. 371 Date May 14, 1998 Sec. 102(e) Date May 14, 1998 PCT Filed Nov. 18, 1996 PCT Pub. No. WO97/19050 PCT Pub. Date May 29, 1997Compounds of formula (I) wherein R1, R2, R3, R4, X are as defined in the specification and are prepared by elimination of one of the groups X1 and X2 from a compound of formula (II) wherein X1 and X2 each independently represent a carboxylic acid group or salt thereof, or a protected carboxylic acid group, the non-eliminated group X1 or X2 corresponding to the group X in the desired compound of formula (I).
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