prov:value
| - that, when A is A1, -x- is nil and R3 is a hydrogen atom; with the further proviso that, when A is A2, -x- is a covalent chemical bond and R3 is nil.Also described herein is a compound as defined above, wherein A is A1 or A2 as above indicated, -x- is a covalent chemical bond or nil, R is hydrogen or acetyl, R1 and R2 independently represent hydrogen, (C1-4)alkyl, benzyloxy, hydroxy-(C2-4) alkyl,
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