Radical-based dephosphorylation and organophosphonate biodegradation and some biosynthetic experiments in sea cucumbers

Part I. Organophosphonates are characterized by a carbon atom covalently bonded to phosphorus. The carbon-phosphorus bond is inert to vigorous acid and base hydrolytic conditions as well as to the action of phosphatase. Nonetheless, Escherichia coli can cleave carbon to phosphorus bonds.; Microbial degradation of organophosphonates is examined with a view to elaborating the chemical basis for the biodegradation. Degradation of a range of alkylphosphonates by E. coli invariably leads to generation of alkane and low levels of alkene.; One possible degradative route is radical-based dephosphorylation. It is envisioned to be initiated by oxidation of the phosphonate to the phosphonyl radical. Fragmentation of the phosphonyl radical would afford an alkyl free radical which could partition between hydrogen atom abstraction and oxidative elimination. Electrochemical oxidation and reaction with lead (IV) tetraacetate are shown to oxidize alkylphosphonates and lead to the formation of alkane and small amounts of alkene. Alkyl free radical intermediacy is underscored by the change in alkane to alkene product ratios upon inclusion of catalytic copper (II) acetate in the reactions of alkylphosphonates with lead (IV) tetraacetate.; Part II. Sea cucumbers, like their close relatives, starfish, have been shown to contain mainly {dollar}Deltasp7{dollar}-sterols. Some laboratories have reported de novo synthesis of {dollar}Deltasp7{dollar}-sterols in sea cucumbers, whereas other reports have suggested that sea cucumber {dollar}Deltasp7{dollar}-sterols may arise by conversion of dietary {dollar}Deltasp5{dollar}-sterols as shown in the starfish.; Experiments in Bohadschia argus, Holothuria mexicana, Holothuria arenicola and Stichopus californicus show that the only sterols synthesized de novo are lanost-9(11)-en-3{dollar}beta{dollar}-ol (1), 4{dollar}alpha{dollar}, 14{dollar}alpha{dollar}-dimethyl-5{dollar}alpha{dollar}-cholest-9(11)-en-3{dollar}beta{dollar}-ol (2) and 14{dollar}alpha{dollar}-methylcholest-9(11)-en-3{dollar}beta{dollar}-ol (3). Squalene does not cyclize to lanosterol or cycloartenol, the sterol intermediates in animals and plants. Instead, lanost-9(11), 24-dien-3{dollar}beta{dollar}-ol, the {dollar}Deltasp{lcub}9(11){rcub}{dollar}-isomer of lanosterol is formed. Sterols (1), (2), and (3) subsequently arise by sequential {dollar}Deltasp{lcub}24{rcub}{dollar}-bond reduction and loss of the 4-methyl groups. This is in marked contrast to the starfish in which synthesis of 5{dollar}alpha{dollar}-cholest-7-en-3{dollar}beta{dollar}-ol and other C{dollar}sb{lcub}27{rcub}{dollar}-sterols occurs de novo via lanosterol, the usual product of squalene cyclization in animals.; The synthesis of {dollar}Deltasp7{dollar}-sterols in Stichopus californicus is shown to occur by modification of {dollar}Deltasp5{dollar}-sterols via formation of a {dollar}Deltasp{lcub}5,7{rcub}{dollar}-diene. This differs from the mechanism in starfish which proceeds through formation of a {dollar}Deltasp4{dollar}-3-keto-sterol intermediate.