Diastereoselective approach to 11-aryl steroid skeletons through a cobalt(I)-mediated [2+2+2] cyclization of allenediynes

The cobalt(I)-mediated [2+2+2] cycloaddition reactions of allenediynes of yne-allene-yne type bearing an aryl group on the allene are described. The cyclizations are totally chemo- and regioselective and show low diastereoselectivities. η⁴-Complexed tricyclic (6,6,6) compounds were obtained in good yields as mixtures of endo/exo diastereomers. The cyclization is also compatible with an oxyfunctionality at C3. By designing an allenediyne having a preexisting D ring, we succeeded in building skeletons of 11-aryl steroids in one step and in a totally diastereoselective manner and with simultaneous introduction of an angular methyl group at C10 and an aryl substituent at C11.     

Theoretical Studies of Inorganic Compounds. 361) Structures and Bonding Analyses of Beryllium Chloro Complexes with Nitrogen Donors

Quantum chemical calculations at various levels of theory (BP86, B3LYP, MP2, CCSD(T), CBS‐QB3) of the beryllium complexes [BeCl₂(NHPH₃)], [BeCl₂(NHPH₃)₂], [BeCl₃(py)]^?, [BeCl₂(NH₃)], [BeCl₂(NH₃)₂], [BeCl₃(py)]^? and [BeCl₃(NH₃)]^? as well as the boron compounds [BCl₃(py)] and [BCl₃(NH₃)] show that BeCl₂ is a very strong Lewis acid. The theoretically predicted bond dissociation energy at CBS‐QB3 of Cl₂Be‐NH₃ (D_e = 32.5 kcal/mol)is even higher than that of Cl₃B‐NH₃ (D_e = 28.6 kcal/mol). Even the second ammonia molecule in [BeCl₂(NH₃)₂] still has a strong bond with D_e = 24.2 kcal/mol. The theoretically predicted bond strengths for the phosphaneimine ligands in [BeCl₂(NHPH₃)₂] are D_e = 46.7 kcal/mol for the first ligand and D_e = 29.8 kcal/mol for the second. The anion BeCl₃^? is a moderately strong Lewis acid which has bond energies of D_e = 14.1 kcal/mol in [BeCl₃(py)]^? and D_e = 14.2 kcal/mol in [BeCl₃(NH₃)]^?. The higher bond energy of [BeCl₂(NH₃)] compared with [BCl₃(NH₃)] comes from less deformation energy for BeCl₂ than for BCl₃. The intrinsic attraction between BeCl₂ and NH₃ calculated with frozen geometries of the complex geometry is ～5 kcal/mol less than the attraction between BCl₃ and NH₃. The bonding analysis with the EDA method shows that the attractive energy of the beryllium complexes comes manly from electrostatic attraction. The larger contribution of the electrostatic term is the most significant difference between the nature of the donor‐acceptor bonds of the beryllium and boron complexes.     

Pterinechemistry. Part 84. A new,regiospecific synthesis of L-biopterin

Pure L -biopterin was obtained in 42% yield by the condensation of 5-deoxy-L -arabinose-phenylhydrazone-triacetate with 4-hydroxy-2,5,6-triaminopyrimidine, followed by iodine oxidation of the formed tetrahydropterin derivative to 1′,2′-O-diacetyl-L -biopterin. Deacetylation was carried out with NH₄OH.     

Fibre-optic oxygen sensor with the fluorescence decay time as the information carrier

In constrast to existing fluoresensors for oxygen, a sensor is described that measures the decay time of the indicator rather than its emission than its emission intensity. A simple opto-electronic device is described for measuring lifetimes of a long-lived fluorophore with a frequency-modulated LED as light source. Measurement of lifetime provides as more linear Stern-Vomer plot and offers certain advantages with respect to the performance of the sensor, because it has an internal reference system that is an attractive to the frequently-used two-wavelenght referencing method. Long-term stability is distinctly better because the phase shift is independent of indicator bleaching and leaching a well as lamp intensity fluctuations. The detection limit is ca. 2 torr of oxygen.     

Synthesis of 5,6-carbonyldioxyindole,a melanogenic cyclic carbonate ester of 5,6-dihydroxyindole

5,6-Carbonyldioxyindole ( 4 ), a melanogenic derivative of 5,6-dihydroxyindole ( 1 ), was synthesized by a procedure starting with 3,4-methylenedioxycinnamic acid ( 5 ). Compound 4 is a stable crystalline solid which is readily hydrolyzed to 1 , a key intermediate on the biosynthetic pathway from tyrosine to melanin.     

Ferrocenyl Sulfinylimide and Diferrocenyl Sulfurdiimide,Fc?NSO and Fc(NSN)Fc

1 Abbreviations and Nomenclature: Fc = η¹-ferrocenyl, CpFe(C₅H₄-); Cp = η⁵-cyclopentadienyl, η⁵-C₅H₅. Compounds containing the —NSO group are designated as either thionylimides, sulfinylimides or N-sulfinylamines. The systematic name is imido oxo sulfuranes(IV).

The reactions of ferrocenylamine, Fc? NH₂ ( 1 ), with thionyl chloride and sulfur dichloride in hexane solution in the presence of triethylamine lead to the title compounds Fc? NSO ( 2 ) and Fc(NSN)Fc ( 3 ), respectively, 2 and 3 have also been obtained in reactions of the silylated ferrocenylamine, Fc? NH(SiMe₃) ( 1b ), with thionyl chloride. The ferrocenyl sulfinylimide 2 has been converted to sulfurdiimides such as Fc(NSN)Fc ( 3 ) and Fc(NSN)R (R = ^tBu ( 4a ), SiMe₃ ( 4b )) by reaction with the lithium derivative of silylated amines, LiN(SiMe₃)R (R = Fc, ^tBu, SiMe₃). The new ferrocenyl compounds 2–4 have been characterized by their NMR spectra, and their electrochemical behaviour has been studied. The molecular structure of Fc? NSO ( 2 ) has been determined by an X-ray structure analysis; the sulfinylimide has the Z configuration, and the —NSO group is coplanar with the cyclopentadienyl ring to which it is attached.     

Über Pterinchemie. 59. Mitteilung [1]. Konformationsanalyse von acylierten 5,6,7,8-Tetrahydropterinen

Conformational Analysis of Acylated 5,6,7,8-Tetrahydropterines The conformation of N(5)-acetates, and of N(5)- and N(8)-trifluoroacetates, respectively, of 6-methyl- and cis-6, 7-dimethyl-tetrahydropterines is studied by ¹H-NMR. spectroscopy. It is shown that the methyl group next to the acylated nitrogen atom is in quasi-axial position.     

Fast structure-based assignment of 15N HSQC spectra of selectively 15N-labeled paramagnetic proteins

A novel strategy for fast NMR resonance assignment of (15)N HSQC spectra of proteins is presented. It requires the structure coordinates of the protein, a paramagnetic center, and one or more residue-selectively (15)N-labeled samples. Comparison of sensitive undecoupled (15)N HSQC spectra recorded of paramagnetic and diamagnetic samples yields data for every cross-peak on pseudocontact shift, paramagnetic relaxation enhancement, cross-correlation between Curie-spin and dipole-dipole relaxation, and residual dipolar coupling. Comparison of these four different paramagnetic quantities with predictions from the three-dimensional structure simultaneously yields the resonance assignment and the anisotropy of the susceptibility tensor of the paramagnetic center. The method is demonstrated with the 30 kDa complex between the N-terminal domain of the epsilon subunit and the theta subunit of Escherichia coli DNA polymerase III. The program PLATYPUS was developed to perform the assignment, provide a measure of reliability of the assignment, and determine the susceptibility tensor anisotropy.     

Reactivity of beta-lactamido N-sulfonyl radicals

[reaction: see text] A new class of N-substituted radical has been studied. Obtained from the corresponding chlorides, beta-lactamido N-sulfonyl radicals were allylated and added onto electron-rich olefins. It has been shown that the radicals do not undergo desulfonylation and are electrophilic in nature.