Partial syntheses of [2α-2H]- and [2α-3H]-gibberellin A29and [2α-2H,-15,17-3H4]gibberellin A51from gibberellin A3

Abstract

In the partial syntheses of the title compounds gibberellin A3(GA3) is ozonised to the norketone and the methyl ester (12) is chlorinated with lithium chloride and toluene-p-sulphonyl chloride to give the 3α-chloro-13-alcohol (15) and its 13-toluene-p-sulphonate (14). The 13-alcohol (15) is converted, by tri-n-butylstannane reduction, then reaction with acetyl hypobromite, and reduction with tri-n-butylstannane, into the 2α-acetoxy-16-ketone (23). This intermediate (23) is converted successively into the 16-ene (24), the 2α-alcohol (25), the 2-ketone (26), [2α-2H]- and [2α-2H]-GA29 methyl esters (29) and (31), and finally into [2α-2H]- and [2α-3H]GA29(30) and (32).An attempt to convert the 3α-chloro-13-toluene-p-sulphonate (14) into GA29 by analogous reactions was abandoned since tri-n-butylstannane reduction of the 2α-acetoxy-13-toluene-p-sulphonates (18) and (19) resulted in extensive loss of the 13-toluene-p-sulphonyloxy-group. However the resultant 13-deoxy-compound (22) was converted into [2α-2H, 15,17-3H2]GA51(37) as for the 13-alcohol (15).