Biosynthesis of psilotin from [2′,3′-13C2,1′-14C,4-3H]phenylalanine studied with 13C-NMR

The 6-phenyl-dihydro-α-pyrone moiety of psilotin is formed from [2′,3′-¹³C₂,1′-¹⁴C,-4-³H]phenylalanine in the plant $\text{Psilotum}$$\text{nudum}$ with retention of all the isotopes.     

Biosynthese de la botryodiplodine,mycotoxine de penicillium roqueforti: Incorporations d'acetate[1-13C], [2-13C], [1-2 13C]et d'acide orsellinique 2-13C-carboxyle 13C], [3-4 13C]

Incorporations of [1-¹³C], [2-¹³C], [1-2¹³C]acetate and [2-¹³C, carboxyl-¹³C], [3-4¹³C]orsellinic acid into botryodiplodin indicate that this mycotoxin is biosynthesized by the polyketide pathway. Orsellinic acid is a precursor of botryodiplodin. A biosynthetic pathway, using orsellinic acid as precursor, is proposed.     

Studies on the biosynthesis of terrecyclic acid A II confirmation of the cyclization mechanism and hydrogen shifts using [2-2H3]acetate and [213C2H3]acetate

Feeding experiments with [2-³H₃]acetate and [2-¹³C²H₃]acetate in $\text{Aspergillus terreus}$ Thom No. 14 indicated that the hydrogen at C-2 in terrecyclic acid A is incorporated without migration from the precursor acetic acid; the results favour our group's earlier speculation for the cyclization to the tricyclic skeleton in the biosynthetic scheme.     

Synthesis of [1-15N,2-13C]-labeled difloxacin

Abstract  

The synthesis of [1-¹⁵N,2-¹³C]-difloxacin, an arylfluoroquinolone antibacterial agent, is reported. As a crucial initial step, the starting materials ethyl 2,4,5-trifluorobenzoylacetate, [formyl-¹³C]-triethyl orthoformate, and [¹⁵N]-4-fluoroaniline were reacted to ethyl [¹⁵N,3-¹³C]-3-(4-fluoroanilino)-2-(2,4,5-trifluorobenzoyl)acrylate. After cyclization and ester cleavage, the resulting intermediate was reacted with 1-methylpiperazine to [1-¹⁵N,2-¹³C]-1-(4-fluorophenyl)-6-fluoro-7-(4-methyl-1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylate, i.e., [1-¹⁵N,2-¹³C]-difloxacin. The overall yield was 62% based on the non-labeled and 43% based on the labeled starting materials (both used in 1.4 molar excess). The product was identified by ¹H-, ¹³C-, and ¹⁵N-NMR spectroscopy and by cochromatography (TLC, HPLC) with an authentic reference; its purity (HPLC) was above 98%. Prior to synthesis of [1-¹⁵N,2-¹³C]-difloxacin, non-labeled difloxacin was synthesized in order to optimize procedures and to identify and characterize all intermediates.     

Substrates to study the mechanism of vitamin D hydroxylation: synthesis of 25-R-[26-2H3]-cholecalciferol

25-R[26-²H₃]-Cholecalciferol has been synthesised from a C-22 aldehyde derived from egosterol and R-3-[²H₃]-methylbutyl bromide. This vitamin is designed to study the mechanism of enzymic hydroxylation at C-25 in the production of 25S, 26-dihydroxycholecalciferol.     

Die enzymatische Synthese von Uridindiphosphoglucose- [1-14C]

Ohne Zusammenfassung     

The temperature dependence of the isotope effects in the polymerization of [α-14C]styrene and [β-14C]styrene

Styrene has been copolymerized with [α-¹⁴C]styrene under radical conditions and with [β-¹⁴C]styrene under both radical and cationic conditions; radical copolymerizations were studied over the temperature range 40–110° and cationic copolymerizations over the range 30–90°. By relating the specific activities of the comonomer feed and of the copolymer, reactivity ratios were found. Arrhenius parameters have been determined for the isotope effects for the propagation steps in each copolymerization. They show that, with [α-¹⁴C]styrene, the difference in the energies of activation predominate in determining the magnitude of the isotope effect; in the case of [β-¹⁴C]styrene, the ratio of the pre-exponential factors is more important under both radical and cationic conditions.     

Proton exchange in dehydromethionine; Synthesis of [C2H3]-L-methionine

Methyl-labelled methionines can be easily prepared via dehydromethionine (1), which undergoes clean exchange at its methyl group with cat. MeONa/MeO²H.     

Biosynthesis of ravidomycin. Use of 13C-13C double quantum NMR to follow precursor incorporation

A biosynthetic scheme is proposed for the ravidomycin aglycone. Incorporation of ¹³C-labeled precursors was followed by conventional and 2-dimensional NMR techniques.     

Photolyse von 2-oxo-[2-13c]-1-diazocyclohexan. Ein beitrag zum oxiren-problem

The synthesis of 2 - oxo - [2 - ¹³C] -1 - diazocyclohexan (10) starting with K¹³CN is described. Photolysis of 10 in dioxan-water yields cyclopentancarboxylic acid containing all the label in the carboxy group, which has been proved by C-13 NMR spectroscopy and electron impact induced fragmentation. The absence of isotope scrambling in the photolytic ring contraction excludes an oxiren participation.