Claude Bauder

Porphyrins from Messel oil shale (Eocene, Germany): Structure elucidation, geochemical and biological significance, and distribution as a function of depth

Abstract The extraction and isolation procedures of twenty nickel porphyrins (seven alkylporphyrins, thirteen carboxylic acids) from lacustrine Messel shale (Eocene, Germany), as well as the unequivocal structural assignments (obtained using 200 and 400 MHz nuclear magnetic resonance (NMR), nuclear Overhauser effect, mass spectrometry and total or partial synthesis of six reference compounds) are described. Ten porphyrins could be specifically correlated with biological precursors: algal chlorophyll c (4), bacteriochlorophylls d (3) and heme (3), while the remaining ones may arise from several chlorophylls. The structures of these fossil pigments mostly confirm the classical “Treibs scheme,” including the origin of some porphyrins from nonchlorophyll sources. They also show that, even in a very immature sediment, deep modifications occur, including, in particular, extensive degradation of chlorophyll E ring. The composition of the porphyrin fractions of Messel oil shale was also studied as a function of depth. A porphyrin acids/alkylporphyrins ratio varying from 0.35 to 24.8 demonstrated that the apparent homogeneity of the shale is not reflected on the molecular scale. This was confirmed when the abundance of the twenty individual porphyrins of known structure was measured along the core. Significant correlations between individual porphyrins were found: fossils of bacteriochlorophylls d , homolog pairs of porphyrins (3-H/3-ethyl), etc.

Evidence for the in situ formation of copper acetylides during Pd/Cu catalyzed synthesis of enynes: a new synthesis of allenynols

The in situ formation of copper acetylide in Pd/Cu catalyzed coupling reactions of acetylenic derivatives has been demonstrated by the reaction with ethynyloxiranes, which provides allenynols; a new Cu catalyzed route to the latter has also been found.

Hemisynthesis of bistramide D by stereoselective reduction of bistramide A. Partial determination of relative and absolute configurations

Abstract The hemisynthesis of bistramide D by stereoselective reduction of bistramide A is reported. The absolute configuration of C4 in bistramide D was also determined and the relative configurations of C6, C9 and C11 in the pyran part, as well as those of C22, C23, C27 and C31 in the spiro moiety of bistramides A and D were also determined by NMR.

Highly stereoselective synthesis of enantiomerically pure β-hydroxy-γ-sulfenyl-γ-butyrolactone by asymmetric Pummerer type cyclization

Abstract Enantiomerically pure t -butyl 4-sulfinyl-3-silyloxy-butanoate can be transformed stereoselectively in a Pummerer reaction with TFAA into the usual aldehyde or into a cis β-hydroxy-γ-sulfenyl-γ-butyrolactone. Experimental conditions allowing total control of the reaction in favor of either the aldehyde or the γ-butyrolactone are described. The corresponding methyl butanoate led, under the same conditions, only to the aldehyde.

Synthesis of derivatives of potent antitumor bistramides D and A leading to the first crystal structure of natural bistramide D

We report a crystalline derivative of bistramide D synthesized from natural bistramide A, and its structure was determined by X-ray analysis.

Asymmetric synthesis of β-hydroxyesters by aldol type condensation of enantiomerically pure t-butyl p-tolyl sulfinyl acetate: unexpected substituent effect on the absolute configuration of the product

Abstract Aldol type condensation of enantiomerically pure t-butyl p-tolyl sulfinyl acetate was shown to give the opposite configuration at the hydroxylic center in the case of an α,β-unsaturated aldehyde, a result which is in sharp contrast with literature results. The absolute configurations of the aldol products were determined by X-ray crystallography.

Total synthesis of chlorophyll c fossils and related petroporphyrins

Abstract The total synthesis of a series of petroporphyrins related to chlorophyll c is described. These compounds have in common, fused to the porphyrin macrocyle, α methylcylopentane ring which was obtained via cyclization of an isopropenyl group.