Molecular and electronic structure of δ-valerothiolactone

The crystal structure of the six-member heterocyclic δ-valerothiolactone (1-thiocycloalkan-2-one) compound has been determined by X-ray diffraction at low temperature, revealing that its skeleton adopts a half-chair conformation. The conformation around the thioester group is almost planar with an anti orientation of the C=O double bond with respect the S-C single bond [C(2)-S(1)-C(6)-O(1) = 176.26(8)°]. The skeletal parameters, especially valence angles [∠C5-C6-S = 121.19(6)°, ∠O=C6-C5 = 122.25(8)°, ∠C6-S-C2 = 106.80(4)°], differ from those typically found in acyclic thioester compounds, symptomatic of the presence of strain effects. The conventional ring strain energy was determined to be 7.5 kcal/mol at the MP2/6-311++G(d,p) level of calculation within the hyperhomodesmotic model approximation. Moreover, the valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.35, 9.50, and 11.53 eV denote ionizations related with the n(S), n(O), and π(C=O) orbitals, respectively, demonstrating the importance of the -SC(O)- group in the outermost electronic properties.     

Baker's yeast reduction of cyclic δ-ketoesters: synthesis and chiroptical properties of condensed δ-lactones

Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters by the use of Saccharomyces cerevisiae. The reactions were not only highly enantioselective but also highly diastereoselective, provided the baker's yeast was preincubated at 50°C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.     

Reaction of 2-alkoxycarbonylmethyl derivatives of δ2-oxazoline and δ2-imidazoline and their tautomers with 4-nitrobenzonitrile N-oxide

It was established that 2-alkoxycarbonylntethylene derivatives of oxazolidine and imidazolidine react readily with 4-nitrobenzonitrile N-oxide; the reaction takes place at the methylidyne carbon atom to give intermediate oximes, which can then undergo cyclization to isoxazoles. Their tautomers —benzimidazole and ² -oxazoline derivatives —react with considerably greater difficulty; in the first case the reaction takes place at a different center, viz., the ring nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 681–684, May, 1991.     

Vapour pressures and enthalpies of vaporization of a series of δ-lactones

Vapour pressures and molar enthalpies of vaporization of a series of δ-lactones (δ-valerolactone (CAS#542-28-9), δ-hexanolactone (CAS#823-22-3), δ-octanolactone (CAS#698-76-0), δ-nonanolactone (CAS#3301-94-8), and δ-decanolactone (CAS#705-86-2)) have been determined by the transpiration method. A linear correlation of enthalpies of vaporization ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}$ at T = 298.15 K of the δ-lactones studied with the number of carbon atoms has been found.     

Microbial bioreductions of γ- and δ-ketoacids and their esters

A series of yeasts were used in the bioreductions of aliphatic and aromatic γ- and δ-ketoacids and esters to investigate the preparation of enantiomerically pure γ- and δ-lactones through the intermediacy of their corresponding γ- and δ-hydroxyacids and esters. Bioreduction of ethyl 4-oxononanoate 2a with Pichia etchellsii afforded the γ-nonanolide (+)-5a with 99% e.e., while Pichia minuta proved to be the best choice for the bioreduction of ethyl 2-oxocyclohexylacetate 2e, which afforded cis-(−)-5e and trans-(−)-5e with 98 and 99% e.e., respectively. Reduction of 3-(2-oxocyclohexyl)propionic acid 3e with Pichia glucozyma gave predominantly the corresponding δ-lactone trans-(−)-6e with 94% e.e., whose absolute configuration was determined by means of CD spectroscopy.     

Syntheses and applications of enantiopure δ-amino acids and their precursors

Enantiopure unnatural homologated amino acids, whereby there is?>?1 carbon atom between the C- and N- termini have found great utility in a number of applications. The enantiopure syntheses of β-amino acids are well documented, as increasingly are those of γ-amino acids. δ-Amino acids on the other hand are much less well-studied despite reports of their potential utility. This review attempts to summarise strategies that have been adopted towards the enantioselective synthesis of δ-amino acids and their precursors (e.g. nitrile/nitro/azido/ester/alcohol etc) and where appropriate demonstrate their utility. Only systems which are all carbon between the two termini are considered and only those where the shortest route between any given C-termini and any given N-termini is four carbons long (i.e. lysine derivatives are not considered).     

Acid-base and complexing properties of some δ-hydroxyalkenylphosphine oxides

Four new compounds, asymmetrical phosphine oxides containing 2-hydroxyphenylethenyl fragment in cis-orientation with respect to the phosphine oxide: dibutyl-, diphenyl-, dibenzyl-, and dinaphthyl-2-(2-hydroxy-5-chlorophenyl)-2-phenyl-ethenylphospnine oxides, have been studied in aqueous ethanol (80 vol % of EtOH) by means of potentiometry and spectrophotometry at 25±0.1°C, and their acid-base and complexing properties estimated.     

State-Selected Unimolecular Decomposition of δ-Valerolactam(+) and δ-Valerolactam(2)(+) Cations: Theory and Experiment

The near threshold photofragmentation pattern of δ-valerolactam(+) and δ-valerolactam(2)(+) has been recorded combining electron/ion coincidence techniques and vacuum ultraviolet synchrotron radiation. The experimental method yields the fragment intensity as a function of the internal energy deposited into the parent cation, up to 3.1 eV above the first ionization threshold. In parallel, ab initio studies on the δ-valerolactam(+) and δ-valerolactam(2)(+) cations and their ionic and neutral fragmentation products have been performed with the aim of determining the isomers of the ionic products observed experimentally as well as of their neutral counterparts. These computations were performed using the PBE0 exchange-correlation functional and the aug-cc-pVDZ basis set. We found good agreement between the calculated reaction enthalpies and experimental appearance energies of the ions. More generally, our experimental and theoretical results reveal that the fragmentation of the ionic species of interest leads to a multitude of neutral and ionic fragments, which may be formed after intramolecular isomerization and complex decomposition processes. Multistep reaction pathways are expected.     

Synthesis of γ-sulfonyl δ-lactones and β-sulfonyl styrenes

A facile route to the synthesis of γ-sulfonyl lactones 5 and β-sulfonyl styrenes 6 has been developed, achieving moderate to good yields via the (1) NaH mediated Michael addition of β-ketosulfones 3 and methyl acrylate in refluxing THF and (2) NaBH₄ mediated stereoselective reduction/lactonization of δ-ketoesters 4 in boiling MeOH, or (3) boron trifluoride etherate mediated ring-opening of lactones 5 in MeOH at reflux.     

Mg-promoted facile and selective intramolecular cyclization of aromatic δ-ketoesters

Treatment of various types of aromatic δ-ketoesters 2, 7, and 9 with Mg-turnings for Grignard reaction at −5 to 0 °C in N,N-dimethylformamide (DMF) containing trimethylsilyl chloride (TMSCl) brought about selective and reductive intramolecular cyclization to give the corresponding α-aryl-α-hydroxycyclopentanones 5, 8, and 10, respectively, in moderate to good yields. Similar reductive intramolecular cyclization of aromatic δ-ketodiesters 14, followed by acidic hydrolysis and decarboxylation easily gave the corresponding 2-aryl-2-cyclopenten-1-ones 15. The present facile coupling may be initiated through electron transfer from Mg metal to the aromatic carbonyl groups of 2, 7, 9, and 14 to generate the corresponding radical anions, followed by their intramolecular nucleophilic attack to the ester groups to give the corresponding five-membered ring compounds 5, 8, 10, and 15, respectively.     

Hydrochlorination of δ2-1,3-oxazolines and 1,3-oxazolidines

The compounds 2-(ethoxycarbonylmethyl)-²-l,3-oxazoline and 1-methyl-2-(methoxycarbonylmethylene)-1,3-oxazolidine are hydrochlorinated at the C=N or C= C bond, respectively, with subsequent opening of the oxazolidine ring. Depending on the reaction conditions, this occurs regioselectively to form various products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 684–686, May, 1992     

Improved water δ2H and δ18O calibration and calculation of measurement uncertainty using a simple software tool

The calibration of all δ(2)H and δ(18)O measurements on the VSMOW/SLAP scale should be performed consistently, based on similar principles, independent of the instrumentation used. The basic principles of a comprehensive calibration strategy are discussed taking water as example. The most common raw data corrections for memory and drift effects are described. Those corrections result in a considerable improvement in data consistency, especially in laboratories analyzing samples of quite variable isotopic composition (e.g. doubly labelled water). The need for a reliable uncertainty assessment for all measurements is discussed and an easy implementation method proposed. A versatile evaluation method based on Excel macros and spreadsheets is presented. It corrects measured raw data for memory and drift effects, performs the calibration and calculates the combined standard uncertainty for each measurement. It allows the easy implementation of the discussed principles in any user laboratory. Following these principles will improve the comparability of data among laboratories.     

Enantioselective Synthesis of δ-Lactones with Lipase-Catalyzed Resolution and Mitsunobu Reaction

Both enantiomers of a series of δ-lactones (e.g., δ-decalactone, δ-dodelactone, and δ-hexadecalactone) were synthesized stereoselectively by Novozym 435–catalyzed resolution. Furthermore, only (S)-enantiomers of δ-lactones were synthesized with a combination of Novozym 435–catalyzed resolution and Mitsunobu reaction.     

Studies on the α-acetylation of δ-valerolactone and ε-caprolactone

The synthetic approach to α-acetylated δ-valero- (7a) and ε-caprolactone (7b) is reported. While 7a was isolated in 21% yield from the respective iodoester 5a by an alkylation sequence involving transesterification and Finkelstein reaction, 7b was not obtained from 5b but the dimer 8. Also transesterification and olefin ring closing metathesis (RCM) failed to prepare 7b. RCM resulted in the dimeric lactone 10, showing that the formation of 14-membered rings is favored over that of seven-membered rings. A Mukaiyama-type Claisen reaction finally gave α-acetyl lactones 7a and 7b in practically useful quantity of about 10 g (62% yield): starting lactones 13a,b were converted to silylenolethers 14a,b, which were acetylated with acetic anhydride in presence of the Lewis acid catalyst TiCl₄. However, acetylation depends on the addition sequence of starting materials: if the mixture of Ac₂O/TiCl₄ is added to 14b, lactone 7b can be further converted to give bis-oxepanonyl ethanols 15a,b. Both compounds 15 were characterized by X-ray crystallography and NMR.     

Hydrothermal synthesis and electrochemistry of a δ-type manganese vanadium oxide

A new manganese vanadium oxide containing double sheets of V₂O₅ layers has been synthesized hydrothermally in the presence of tetramethylammonium ions. It has the electrochemically active δ-V₂O₅ structure, variants of which are found in V₆O₁₃ and xerogel vanadium oxides. The manganese ions, together with the N(CH₃)₄ ions, reside in a disordered manner between the oxide sheets. The δ-type [N(CH₃)₄]_zMn_yV₂O₅·nH₂O has a monoclinic structure, a=11.66(2) Å, b=3.610(9) Å, c=13.91(4) Å, β=108.8(2)°. It reacts readily with lithium with a capacity exceeding 220 mAh g⁻¹; the organic ions do not impede reaction as in the single sheet V₂O₅ materials, such as N(CH₃)₄V₃O₇.     

Synthesis and properties of a sterically unencumbered δ-silanediol amino acid

An amino acid carrying a 1-(4-dihydroxymethylsilyl)butyl side chain has been prepared in enantiomerically pure form as a potential inhibitor of the enzyme arginase, a pharmaceutical target. As a water-soluble silanediol, this compound was anticipated to be entropically stabilized against polymerization and siloxane formation. At 50 mM in D(2)O, the degree of oligomerization was found to be pH dependent, with diastereomeric mixtures formed on condensation. Above pH 11 the silane is largely monomeric.     

Synthesis and characterization of Al doped δ-laminar crystal sodium silicate

An modified laminar crystal sodium silicate(Al-SKS-6)was synthesized by spray drying and high temperature crystallization using sodium silicate as silicon source,Al atom as inorganic source and hexadecyltrimethy ammomum bromide(CTMAB)as the structure template.The hydrothermal stability of product was at least 1 h.The synthesized material was characterized by XRD and SEM.The results indicated that shape and intensity of XRD diffraction peak at 20 took changes.but raw material δ phase crystal form kept unchanged.and assured high Ca2+ and Mg2+ binding capacity of the products.The Ca2+ and Mg2+ binding capacity of product is up to 380 mg Ca/g and 410mg Mg/g respectively.It was found that the hole of product became smaller and appeared rod structure based on SEM. The hydrothermal stability was increased due to the pillaring of A1 atom.     

Simultaneous measurement of δH, δO,and δO in H2O using a commercial cavity ringdown spectrometer

We demonstrate that a commercial instrument that provides measurements of ¹⁸O/¹⁶O and D/H ratios in water samples can be modified to also provide measurements of ¹⁷O/¹⁶O. This additional capability and associated precision allows for the discernment between conventional mass-dependent processes, such as isotope exchange and evaporation and mass-independent processes that arise from non-equilibrium chemical and photochemical processes. We demonstrate this resolution by performing a series of experiments including evaporation and reservoir-mixing with ¹⁷O enriched water samples followed by evaporation. The ability to simultaneously measure ¹⁶O, ¹⁷O, and ¹⁸O abundances in water samples using the procedures described here should help to facilitate multi-isotopic studies of water (and other compounds) in astrochemical, geochemical, and biological studies.     

Enzymatic resolution of analgesics: δ-hydroxytramadol, ε-hydroxytramadol and O-desmethyltramadol

Efficient enzymatic resolutions of the analgesic δ-hydroxytramadol rac-3 and ε-hydroxytramadol rac-4 have been achieved through pig liver esterase- and Candida rugosa lipase-catalyzed hydrolyses of the corresponding butyrates. The Candida rugosa lipase-catalyzed hydrolysis of O-desmethyltramadol butyrate rac-8a, having a remote aromatic acyloxy group as the only functional group amendable to a hydrolase-catalyzed reaction, proceeded with a good selectivity.