prov:value
| - A method in accordance with claim 14, wherein R1 and R2 each independently are a benzyl group, a 2-phenethyl group, a 3-phenylpropyl group or a group of formula III or IV, wherein the groups A1 and A2 are methylene, 1,2-ethanediyl or 1,3-propanediyl and A is methylene, phenylmethylene, 2-phenylethane-1.1-diyl, 1,2-ethanediyl or 1,3- propanediyl, whereby the respective aryl and heteroaryl groups ar
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