| 摘要 |
Compounds of the formula (1), in which R1 is hydrogen, methyl or hydroxymethyl, R2a and R2b are both hydrogen or together denote a bond, R3 i s 1-7C-alkyl, R4 is 1-7-alkyl and R5 is 1-7C-alkyl, and its salts, are valuabl e intermediates for preparing active compounds for the prevention and treatmen t of gastrointestinal diseases.
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