Borohydride tritium-labeled, preparation

Gabriel and Ashwell463 prepared tritium-labeled sucrose and a-D-[3-3H]-allopyranosyl /i-1)-fructofuranoside by reduction of a-D-rzZw-hexopyranosyl-3-ulose /i-D-fruetoluranoside ( 3-ketosucrose, 247) with tritiated borohydride. 

Since ivermectin (= 22,23-dihydroavermectin B ) is obtained by catalytic reduction of avermectin B, the same procedure using tritium gas convenientiy affords tritiated ivermectin (22,23- [JT]-22,23-dihydroavermectin B ). The preparation of a tritiated derivative containing a 22,23-double bond starts with the readily available 5-ketone, which is reduced with [JT]-sodium borohydride stereospecificaHy to a 5- [JT]-derivative (40). Carbon-14 labeled avermectins can be obtained by a biosynthetic process using sodium (l- C)propionate as labeled precursor (48). 

The borohydride reduction of 2 - and 3 -ketocytidine derivatives having or lacking an N4-acetyl group provided a facile route to cytosine nucleosides labeled with tritium at specific positions of the sugar.28 Reduction of either 20a or 20c with sodium borohydride in ethanol-benzene afforded the arabino and the ribo derivatives in the ratio of 4 1. Treatment of the reduction mixture with methanolic ammonium hydroxide gave the deacetylation products, 82b and 19b, isolated in crystalline form by preparative, thin-layer chromatography. 

Either this synthesis or that shown in Scheme 16 is suitable for the preparation of C6 deuterated or tritated derivatives of L-ascorbic acid reducing 27 with deuterium or tritium enriched gas or with labeled sodium borohydride (51). 

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