| http://www.w3.org/ns/prov#value | - In other embodiments, the compounds of formula (I) are those having formula (IX) [see, e.g., U.S. Pat. No. 4,013,668] or N-oxides thereof and other pharmaceutically acceptable derivatives: in which R19 is lower alkyl; R18 is hydrogen or lower alkanoyl containing 2 to 7, preferably 2 or 3, carbon atoms, or preferably R18 is hydrogen or acetyl, and is attached at the 5 or 6 position in either the en
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