Brian A. Marples

Epoxidation with dioxiranes derived from 2-fluoro-2-substituted-1-tetralones and -1-indanones

Abstract Homochiral 2-fluoro-2-substituted-1-tetralones ( 10a , 10b , 13 ) and ethyl 2-fluoro-1-indanone-2-carboxylate ( 16 ) have been isolated. The dioxirane derivatives of these ketones have been prepared in situ , and have been shown to epoxidise alkenes but not enantioselectively. The dioxirane derivative of methyl 2,5,7-trifluoro-1-indanone-2-carboxylate ( 18 ) has been shown to be comparatively efficient in epoxidation.

Dioxirane mediated steroidal alkene epoxidations and oxygen insertion into carbon-hydrogen bonds

Abstract Dioxirane generated in situ from a range of ketones afforded the 5,6-epoxides in high yield from cholesterol or its acetate. The α:β ratio was close to 1 in contrast to that observed for peroxyacids ( ca . 4). 4,4-Dimethylcholesterol and its acetate were not epoxidised but were oxidised respectively to the 3,7-dioxo- and the 7-oxo-derivative respectively with dimethyldioxirane. Oxidations of steroidal alcohols were shown to proceed via an oxygen insertion mechanism by use of 18 O-labelled substrates and 5α-cholestan-3α-ol was oxidised more quickly (>1.5 x) than its 3β-epimer.

APPLICATIONS OF FREE AND RESIN-BOUND NOVEL (TRIFLUOROMETHYL)DIOXIRANES

Abstract Recyclable resin-bound and other trifluoromethyl aryl ketones are efficient catalysts for oxone ® mediated epoxidations.

Regioselective 2-hydroxylation of 3-methoxyoestra-1,3,5(10)-trienes via chromium carbonyl complexes

Abstract Deprotonation, with BuLi, of (n6arene) Cr(CO)3 complexes derived from 3-methoxyoestra-1,3,5(10) trienes followed by reaction with MoOPH leads to the 2-hydroxy-3-methoxy-derivatives in satisfactory yield.

Reversible cleavage of 5-cholest-3-enoxyl radicals: addition of alkyl radicals to ketones

Abstract Oxiranylcarbinyl radicals (4) formed by photolysis of 3β-acetoxy-4 ξ, 5 ξ-epoxycholestanes in HMPA/H 2 O and by Bu 3 SnH reduction of 4ξ,5ξ-epoxy-3 β-[imidazol-1-yl(thiocarbonyl)oxy]-cholestanes gave the 5-cholest-3-enoxyl radicals which underwent reversible cleavage of the C5–C10 bond.

An investigation into the β-cleavage of aziridinylcarbinyl radicals

Abstract In contrast to similar oxiranylcarbinyl radical systems, 3-arylaziridinylcarbinyl radicals have been shown to give only products of CN bond cleavage.

Radical reactions of bicyclo[2.2.1]heptan-3-spiro-2′-oxiranes

Abstract Tributyltin hydride reduction of 2-bromo- and 2-keto-bicyclo[2.2.1]heptan-3-spiro-2′-oxiranes gives ring opening of the oxirane-rings via intermediate 3-(spiro-2′-oxiranyl)bicyclo[2.2.1]heptan-2-yl radicals, whereas reduction of the analogous 2-(thiocarbonyl)imidazolides) [2-(O-CS-Im)] unusually yields the 2-methoxy derivatives and does not proceed by the expected normal fragmentation to yield 3-(spiro-2′-oxiranyl)bicyclo[2.2.1]heptan-2-yl radicals and subsequent ring-opening of the oxirane rings.

Enantioselective lipase-catalysed hydrolysis of esters of epoxy secondary alcohols: An alternative to Sharpless oxidation

The enantioselectivity and yield of lipase-catalysed hydrolyses of epoxy butanoates (4) depends on R. Sharpless oxidation of the secondary allylic alcohol (8,R2Pr) established that in the lipase-catalysed hydrolysis of (4,R2Pr) the threo-isomer gave higher ee than the erythro-isomer.

Synthesis and cytotoxic activity of estrogen α-methylene-δ-lactones

Abstract Several estrogen derivatives containing the α-methylene-δ-lactone group as part of the D-ring were prepared as anti-tumor agents. The compounds were highly toxic towards HeLa S3 cells grown in culture.

SYNTHESIS OF NOVEL STEROIDAL INHIBITORS OF HIV-1 PROTEASE

The design and synthesis of potential steroidal HIV-1 protease inhibitors is described. Compounds derived from 11-amino-12-keto-cholanic acid derivatives show modest activity.