prov:value
| - where R. sup. 1, R. sup. 2 and R. sup. 3 are the same or different hydrogen or organic groups including alkyl groups, alkenyl groups, alkynyl groups, aryl groups, arylalkyl groups, alkoxy groups, aryloxy groups; X is a Group IIIA or Group VA element; R. sup. 4 is a steroidal group, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an arylalkyl group, an alkoxy group or an aryloxy
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