prov:value
| - Where R20 is other than H it is preferably selected from alkyl, especially C1-4 -alkyl; aryl, especially phenyl; epoxy, --CO-C2-6 -alkenyl, especially acryloyl; --NHCO-C2-6 -alkenyl, especially acryloylamido; or, where X is NR, R and R20 may be linked to form, with the N atom, a 5-, 6- or 7-membered heterocycle.
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