New β-ketophosphonates for the synthesis of prostaglandin analogues. 1. Phosphonates with a bicyclo[3.3.0]octene scaffold spaced by a methylene group from the β-ketone.

The synthesis of β-ketophosphonates, linked by a methylene group to a bicyclo[3.3.0]octene fragment, was performed by the reaction of dimethyl methanephosphonate with the ester group of two intermediates with this scaffold. Starting from a diol, protected with good leaving groups (mesyl and tosyl), we performed a sequence of reactions with good yields: the carbon chain lengthening by reaction with KCN, the hydrolysis of the nitrile groups to carboxyl, the esterification of carboxyl to ester and finally the phosphonate synthesis, which gave one bis-β-ketophosphonate and two mono β-ketophosphonates. The new β-ketophosphonates are key intermediates for obtaining new prostaglandin analogues with a bicyclo[3.3.0]octene fragment in the ω-side chain. The bicyclo[3.3.0]octane scaffold, found in natural products and in anticancer compounds, are expected to keep their activity in PG analogs; the bulky scaffold, separated by a methylene group from the C-15 carbon atom, is expected to diminish the inactivation of the PG analog by enzyme oxidation of 15α-OH oxidation to 15-Keto via PGDH pathway.