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β-Ketophosphonates with pentalenofurane fragments linked to the keto group were synthesized. The bulky pentalenofurane skeleton is expected to introduce more hindrance in the prostaglandin analogues of type <b>III</b>, greater than that obtained with the bicyclo[3.3.0]oct(a)ene fragments of prostaglandin analogues <b>I</b> and <b>II</b>, to slow down (retard) the inactivation of the prostaglandin analogues by oxidation of 15α-OH to the 15-keto group via the 15-PGDH pathway. Their synthesis was performed by a sequence of three high yield reactions, starting from the pentalenofurane alcohols <b>2</b>, oxidation of alcohols to acids <b>3</b>, esterification of acids <b>3</b> to methyl esters <b>4</b> and reaction of the esters <b>4</b> with lithium salt of dimethyl methanephosphonate at low temperature. The secondary compounds <b>6b</b> and <b>6c</b> were formed in small amounts in the oxidation reactions of <b>2b</b> and <b>2c</b>, and the NMR spectroscopy showed that their structure is that of an ester of the acid with the starting alcohol. Their molecular structures were confirmed by single crystal X-ray determination method for <b>6c</b> and XRPD powder method for <b>6b</b>.