Thirty-eight fossil coral samples of known age from late Pleistocene uplifted reef terraces have been analyzed for amino acid composition and for the degree of racemization of selected amino acids. Particular attention has been given to the epimerization (racemization about the cc-carbon) of isoleucine. The D/L ratios observed in many of these samples do not conform to the concept of increaqing...

Several aspects of mathematical astrobiology are discussed. It is argued that around the time of the origin of life the handedness of biomolecules must have established itself through an instability. Possible pathways of producing a certain handedness include mechanisms involving either autocatalysis or, alternatively, epimerization as governing effects. Concepts for establishing hereditary inf...

N-Methylation of peptides is an important synthetic tool in peptide-based medicinal chemistry. Herein, an optimized strategy for solid-phase synthesis of small but highly N-methylated cyclic peptides is described. The proposed route addresses several problems associated with the synthesis of peptides containing several sequential N-methyl-amino acids, such as in situ N-methylation, difficulty o...

In the pathway of hydrosyproline metabolism by an inducible strain of Pseudomonas (1)) an initial reaction involves the reversible epimerization of hydroxy-L-proline to allohydroxy-n-proline by racemization at carbon 2. In subsequent steps of this sequence, allohydrosy-n-proline is oxidized to Al-pyrrolinelhydroxy2carboxylate (2) and the latter compound is oxidized to ar-ketoglutarate through a...

Flavaglines are a class of natural products with potent insecticidal and anticancer activities. β-Lactones are a privileged structural motif found in both therapeutic agents and chemical probes. Herein, we report the synthesis, unexpected light-driven di-epimerization, and activity-based protein profiling of a novel rocaglate-derived β-lactone. In addition to in vitro inhibition of the serine h...

The oxidation of norbornane by a reconstituted liver cytochrome P-450 system affords exoand endo-2-norborneol in a ratio of 3.4:1. The ratio ofese products was found to be 0.76:l when exo!exo,exo,exo-2,3,5,6-tetradueteronorbornane --was oxidized. Analysis of the mass spectra of the products from the deuterated hydrocarbon showed that 25% of the exo-norborneol contained four deuterium atoms wher...

The total syntheses of the Lythracea alkaloids (+)-vertine and (+)-lythrine are described. Enantioenriched pelletierine is used as a chiral building block and engaged into a two step pelletierine condensation leading to two quinolizidin-2-one diastereomers in a 8 : 1 ratio. The major product is used in the synthesis of (+)-vertine via aryl-aryl coupling and ring closing metathesis to provide a ...

Schubert, Wehrberger & Frankenberg (1964) first isolated and identified 6a-hydroxytestosterone as a metabolite in human urine after intravenous administration oftestosterone to adult women. The tissue site of O6c-hydroxylation was unknown, and it could not be excluded that the metabolite had arisen by epimerization of 6fl-hydroxytestosterone. Recently we demonstrated that testosterone is hydrox...

Mannuronan C-5 epimerases (ManC5-Es) are produced by brown algae and some bacteria, such as Azotobacter Pseudomonas species. It can convert the transformation of β-D-mannuronic acid (M) to α-L-guluronic (G) in alginate with different patterns epimerization. Alginate compositions monomer sequences possess properties functions, which have been utilized industries for various purposes. Therefore, ...

The title compound 1-exo (with minor amounts of its C8 epimer 1-endo) was prepared by Wolff-Kishner reduction of the cycloadduct of 1,3-cyclohexadiene and cyclopropylketene. The [1,3]-migration product 2-endo was synthesized by efficient selective cyclopropanation of endo-5-vinylbicyclo[2.2.2]oct-2-ene at the exocyclic π-bond. Gas phase thermal reactions of 1-exo afforded C8 epimerization to 1-...