Mixture Of Dl Research Articles

Fourier Transform Infrared (FTIR) Spectroscopic Analysis of Amino Acid Serine for its Chiral Identification

Synthesis of chiral drugs required chiral starting materials organic compounds. DL serine is an amino acid that is used as a key starting material in the synthesis of many drug substances. D or L isomer of Serine will lead to the chiral drug substances whereas DL mixture will lead to racemic drug substances. FTIR can be used as the primary analytical tool for the identification of Serine isomers and its racemic mixture. Many absorption bands in FTIR spectra identify whether a molecule is a specific isomer or racemic mixture. A systematic comparison of FTIR spectroscopic data is carried out revealing that the compound is the specific isomer and the racemic mixture shows different spectra with different bands.

Iodine-promoted oxidative homocoupling of methyl 2-arylacetates under equilibrium conditions using potassium tert-butoxide as a base

Iodine-promoted dimerization of enolates of methyl 2-arylacetates generated with tBuOK under equilibrium conditions are reported. The oxidative homocoupling reaction furnishes a mixture of dl and meso dimers in moderate to good yields and diastereoselectivity. Electron-withdrawing substituents on the aryl ring seem to facilitate dimerization leading to higher yields and ortho-substituted aryl acetates afford better diastereoselectivity.

ChemInform Abstract: Pinacol Couplings of a Series of Aldehydes and Ketones with SmI2/Sm/Me3SiCl in DME.

AbstractFollowing the title reaction, aryl aldehydes and arylmethyl ketones are transformed to the corresponding pinacol coupling products in high yields and as mixtures of dl and meso diastereomers.

ChemInform Abstract: Reductive Coupling of Aromatic N,N‐Acetals Using Zinc and Chlorotrimethylsilane.

AbstractAromatic N,N‐acetals and N,O‐acetal (X), activated by TmsCl, are coupled in the presence of zinc to give mixtures of dl‐ and meso‐diamines.

A Convergent Pd‐Catalyzed Asymmetric Allylic Alkylation of dl‐ and meso‐Divinylethylene Carbonate: Enantioselective Synthesis of (+)‐Australine Hydrochloride and Formal Synthesis of Isoaltholactone

The use of a mixture of dl- and meso-divinylethylene carbonate as an electrophile in palladium-catalyzed asymmetric allylic alkylation reactions is reported. From the diastereomeric mixture of meso and chiral racemic starting materials, a single product is obtained in high optical purity employing either oxygen or nitrogen nucleophiles. The resulting dienes have proven to be versatile synthetic intermediates as each carbon is functionalized for further transformation and differentiated by virtue of the reaction. A mechanism for this intriguing transformation is proposed and a concise enantioselective total synthesis of (+)-australine hydrochloride is reported as well as a formal synthesis of isoaltholactone.

Convergent Asymmetric Alkylation from meso and dl Carbonates

In the presence of a chiral catalyst system for allylic alkylation, meso and dl allylic carbonates generate a single product in excellent yield and enantiomeric excess. The reactions can be performed with either meso or dl compounds, or a combination of the two compounds into one flask to generate the same product. The maximum yield of the dl mixture is 50%, as the R,R-enantio­mer is inactive, whereas the meso compound is completely active; thus a mixture of the two has a maximum yield of 75%.

Palladium-Catalyzed Asymmetric Allylic Alkylation of meso- and dl-1,2-Divinylethylene Carbonate

The palladium-catalyzed asymmetric allylic alkylation of a 1:1 mixture of dl- and meso-1,2-divinylethylene carbonate is reported. For the first time, both the ionization and nucleophilic addition steps of the catalytic cycle act as enantiodiscriminating steps to give a single product in high enantiomeric excess. The reactions proceed in >98% ee to efficiently generate useful chiral building blocks from acrolein. The absolute and relative configurations of iso-cladospolide B and 11-epi-iso-cladospolide B were verified by total synthesis, solving an apparent discrepancy in the literature.

(Phenylthiomethyl)silanes and (butyltelluromethyl)silanes as novel bifunctional ligands for the construction of dithioether-, ditelluroether- and transition metal–silicon complexes

The functionalized silanes (PhSCH 2) 2SiPh 2 ( 1a), (PhSCH 2) 2Si(vinyl)Me ( 1b), (PhSCH 2) 2Si(H)Me ( 1c) and (PhSCH 2) 3SiH ( 1d) have been prepared and co-ordinated as chelating dithioether ligands or via a covalent MSi bond to various transition metal centers. Thus, reaction of 1a with [PtCl 2(PhCN) 2] affords the dithioether complex cis-[PtCl 2{(PhSCH 2) 2SiPh 2}] ( 3), which exist in solution as mixtures of dl- and meso-invertomers. Treatment of [Re(μ-Br)(CO) 3THF] 2 with 1a– c yielded the stereochemically rigid chelate complexes fac-[ReBr(CO) 3{(PhSCH 2) 2SiR 1R 2}] (R 1, R 2=Ph ( 4a)), (R 1=vinyl, R 2=Me ( 4b)), (R 1=H, R 2=Me ( 4c)). Due to the presence of two different substituents R 1 and R 2 on Si, 4b and 4c are isolated as 50:50 mixtures of diastereomers. The presence of a SiH function in 1c, d can be exploited for SiH activation reactions. Thus, oxidative addition on [Pt(PPh 3) 2(CH 2CH 2)] yields the fluxional hydrido silyl complex [Pt(H)(PPh 3) 2{Si(CH 2SPh) 2Me}] ( 5a) and the rigid derivative [Pt(H)(PPh 3) 2{Si(CH 2SPh) 3}] ( 5b). The ditelluroether complexes cis-[PtCl 2{(RTeCH 2) 2SiMe 2)] ( 6a, R=Ph), ( 6b, R=n-Bu) are obtained by treatment of [PtCl 2(PhCN) 2] with (PhTeCH 2) 2SiMe 2 ( 2a) and (n-BuTeCH 2) 2SiMe 2 ( 2b), respectively. The complex fac-[ReBr(CO) 3{(n-BuTeCH 2) 2SiMe 2}] ( 7) results from the reaction of [Re(μ-Br)(CO) 3THF] 2 with ( 2b). The new compounds have been studied by multinuclear NMR techniques, the crystal structures of 3, 4a, 5 and 6b have been determined by X-ray diffraction studies.

Determination of d-alanine in the rat central nervous system and periphery using column-switching high-performance liquid chromatography

A column-switching chiral HPLC system for the determination of minute amounts of d-Ala in mammalian tissues has been established. d-Ala and its l-enantiomer are purified as a dl mixture on a micro-ODS column after precolumn fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole and are introduced to a chiral column to determine each enantiomer. The calibration curve of d-Ala spiked into a rat cerebellum sample is linear from 5 to 5000 fmol with a correlation coefficient of 1.0000. The lower limit of quantitation of d-Ala is 5 fmol ( S/ N=5). Within-day and day-to-day precisions of spiked d-Ala (15 fmol) are 3.9 and 4.8% (R.S.D), respectively. With this system, the anatomical distribution of free d-Ala in the rat central nervous system and periphery has been investigated. Among the 22 examined tissues of the rat, the highest amount of d-Ala has been observed in the anterior pituitary gland ( 86.4±9.9 nmol/g wet tissue), and the second highest amount has been observed in the pancreas ( 29.2±5.0 nmol/g wet tissue). Postnatal and day–night changes in d-Ala amounts in the anterior pituitary gland have also been studied. The amount of d-Ala is highest at 6 weeks of age and significantly decreases with age, and the amount of d-Ala is significantly higher during the daytime than during the nighttime.

Determination of minute amounts of d-leucine in various brain regions of rat and mouse using column-switching high-performance liquid chromatography

A highly sensitive method for the determination of minute amounts of d-Leu in biological samples was developed. For accurate and sensitive determination, a column-switching system using a micro ODS column and a chiral column was adopted. After pre-column derivatization of d- and l-Leu with NBD-F, the derivatives of the enantiomers were purified on a micro ODS column as a dl mixture. The eluted dl-Leu was then introduced to the chiral column, and each enantiomer was determined. The calibration curve for d-Leu, which was constructed by adding known amounts of d-Leu to a rat hippocampus, was linear from 1 to 1000 fmol ( r>0.999), and the detection limit of added d-Leu was 1 fmol ( S/ N=5). Within-day and day-to-day precisions of d-Leu determination using the same homogenate of rat hippocampus were 5.11 and 5.25% (RSD), respectively. The content of d-Leu in rat hippocampus was 0.69 nmol/g wet tissue (the percentage of d-enantiomer for total Leu was 0.97%), which was consistent with the reported value. The distribution of d-Leu in mouse brain was also investigated, and the presence of d-Leu in various regions of the mammalian brain was first observed.

Dialkylation of acetophenones and acetophenone ethylene ketals with 1,8-bis(trimethylsilyl)-2,6-octadiene (BISTRO). Semi-empirical SCF studies of α-methoxy-α-methylbenzyl cations

Titanium tetrachloride mediated dialkylation of acetophenones or acetophenone ethylene ketals by 1,8-bis(trimethylsilyl)-2,6-octadiene (BISTRO) leads to a mixture of dl and meso 1-alkyl-1-phenyl-2,5-divinylcyclopentanes. Better yields are observed with p-bromoacetophenone and m-methoxyacetophenone.

Synthesis of mixtures of [2H6]myo‐inositol monophosphates suitable as internal standards for quantitative GC/MS and a simple synthesis of DL‐myo‐inositol‐1‐phosphate

AbstractA mixture of DL‐[2H6]myo‐inositol‐1‐ and ‐4‐phosphate and (meso) myo‐inositol‐2‐ and ‐5‐phosphate is readily prepared on a 100 milligram scale from the mixed isomers of di‐O‐cyclohexylidene‐[2H6]myo‐inositol by phosphorylation with tetrabenzylpyrophosphate. The deblocked [2H6]myo‐inositol monophosphate isomers are obtained where the relative amounts of racemic myo‐inositol‐1‐phosphate ≥ ‐4‐phosphate ≥ ‐2‐phosphate ≥ ‐5‐phosphate. In addition a simple synthesis of DL‐myo‐inositol‐1‐phosphate was developed which was found to be unsatisfactory for the preparation of deuterium‐labeled product.

ChemInform Abstract: Diastereomeric Selective Formation of a Linear Diphosphazane: meso‐iPrN(PhP(iPrNH))2.

AbstractReaction of PhPCl2 (I) with more than two equiv. iPrNH2 (II) and NEt3 yields a meso:dl mixture of the title compound (III) along with the diaminophosphine (IV).

Potential radiopharmaceuticals for the detection of ocular melanoma. Part III. A study with 14C and 11C labelled tyrosine and dihydroxyphenylalanine.

In order to investigate the possibility of using [1-11C] labelled 3,4-dihydroxyphenylalanine (DOPA) and tyrosine as radiopharmaceuticals for the detection of eye melanoma, the biodistributions of the same 1- and 3-14C-labelled compounds were investigated in Syrian golden hamsters with Greene melanoma. The results of these investigations were compared with positron emission tomography (PET) images of 11C labelled DOPA and tyrosine. The synthesis of these 11C labelled compounds procures of DL mixture, from which D and L forms can be separated. One h after intravenous injection, both 14C labelled DL-, L- and D-DOPA showed a high uptake in tumour tissue, that of DL- and D-DOPA being the highest. These high uptakes, together with relatively low uptake in bone, skin and eye resulted in high tumour/non tumour ratio (for DL-DOPA 5.9, 4.5 and 6.6 respectively). Extraction of the tumour tissue with trichloroacetic acid showed that L-DOPA was mainly incorporated into melanin, whereas D-DOPA was not. Also, the uptake 1 h after intravenous injection of 1-14C-L- and DL-tyrosine into the tumour were high, but L- and DL- were less different; tumour/non tumour ratios were favorable. PET images of the tumour obtained 40-80 min after injection of the [1-11C] labelled DOPA and tyrosine confirmed that melanoma detection was promising and that D-DOPA produced a better melanoma image than L-DOPA.

ChemInform Abstract: Concave Functionality: Design of a Phenol Sticky Host.

AbstractCyclization of the tetrakis‐acetylenic pyridine (III), prepared by standard procedures from bis(propargyloxy)naphthoic acid (I) and pyridine (II) (no details given), afforded a 2:1 mixture of dl‐ (V) and meso‐host (IV) (yields not given).

Energetics of proline racemase: transition-state fractionation factors for the two protons involved in the catalytic steps.

The isotope effects for the interconversion of L-proline and D-proline, catalyzed by proline racemase, have been determined in the saturated region with both [2-2H]proline and [2-3H]proline. The deuterium fractionation factors for each of the protons in flight have been obtained from two kinds of experiment: by measuring the rate of racemization of one [2-2H]proline enantiomer as it racemizes into an equilibrated pool of unlabeled proline and by measuring the deuterium content of a proline sample at the optical rotation maximum that occurs when an equimolar mixture of one deuterium-labeled enantiomer and the other unlabeled enantiomer runs to equilibrium. The tritium fractionation factors for each of the protons in flight have been determined from measurements of the rate of loss of tritium to the solvent as one [2-3H]proline enantiomer runs to equilibrium. Good agreement is found among the fractionation factors determined by each method. The deuterium fractionation factors for the two protons are not identical: that for the proton derived from L-proline is 0.375 and that for the proton derived from D-proline is 0.44. This difference has been confirmed by a double-competition experiment in which the optical rotation of a mixture of DL-[2-2H]proline and unlabeled DL-proline is followed with time. The rotation (initially zero) passes through a maximum, from which the ratio of the two fractionation factors (0.86) is obtained. These data, coupled with the equilibrium fractionation factor for the 2-position of proline (which has been determined to be 1.17), provide the transition-state factors for each of the in-flight protons, and delineate the nature of the transition state(s) for the enzyme-catalyzed racemization.

The biosynthetic incorporation of [phenyl-3H]phenylalanine into gliotoxin

When mixtures of DL-[2′,4′,6′-3H3]-m-tyrosine and DL-[1-14C]phenylalanine were fed to cultures of Gliocladium deliquescens good incorporation (4.9 and 1.6% in separate experiments) of 14C and negligible incorporation (ca. 0.04%) of 3H into the derived gliotoxin (2) was observed. Incorporation of DL-[1-14C, 3′-3H]-, DL-[1-14C, 2′-3H]-, and L-[1-14C, 4′-3H]-phenylalanine into gliotoxin occurred without loss of tritium. Degradation of the [14C, 3H]gliotoxin gave, in each case, bis(anhydro-dethio) gliotoxin (3) and dehydrogliotoxin (4) having a tritium content indicating that the incorporation of phenylalanine had occurred without migration of tritium. These results, taken together, show that neither m-tyrosine (3′-hydroxyphenylalanine) nor any other hydroxybenzene derivative can be an obligatory intermediate on the biosynthetic pathway from phenylalanine to gliotoxin. The possible involvement of arene oxides in gliotoxin biosynthesis is discussed.

Responses of Honey Bees (Apis Mellifera) to Amino Acid Solutions Mimicking Floral Nectars

Amino acids are probably ubiquitous components of floral and extrafloral nectars. Although it seems likely that they serve, as sugars do, to reward nectarivores, little is known about the responses to amino acids by flower visitors. The experiments reported here were conducted to determine the responses of honey bees (Apis mellifera) to single amino acids at relatively high concentrations dissolved in an aqueous solution of 30% sucrose. Bees' responses to 24 L—amino acids, 2 DL mixtures, 2 phenolics, and a flavonoid were tested with artificial—flower feeders. The bees' responses were classified as: (1) consumption that generally declined as amino acid concentration increased (although weak solutions of amino acids were sometimes preferred over a sucrose control), (2) a preference for the strongest concentration offered (phenylalanine), (3) no significant difference between the amino and acid and control. There were no apparent correlations between characteristics of the amino acids and the bees' reactions to them, and no obvious difference between responses to essential and nonessential amino acids.

Association of optically active ions III: diastereomeric ion pair formation in histidine-glutamic acid mixtures

Abstract Conductometric titrations of equimolar mixtures of L-glutamic acid and L-histidine indicate that these species interact more strongly than L-glutamic acid with D-histidine in dilute solution. The presence of ion pairs is confirmed by the UV spectrum of these solutions. No such stereospecific interactions were found between L-glutamic acid and L-lysine or L-ornithine. The conductometric titration curves of these compounds are identical with that of L-glutamic acid with the DL mixture of the basic amino acids.

Dynamic Mechanical Behavior of DL Mixtures of Poly(γ-benzyl glutamate)

The dynamic mechanical properties of mixtures of poly(γ-benzyl D-glutamate) and poly(γ-benzyl L-glutamate) were studied as functions of frequency, temperature, and the molar ratio of D to L. The results obtained were interpreted in terms of the stacking of benzene rings of the D and L polymers on top of each other. The dependence of the relaxation strength of the dispersion at room temperature on the molar ratio of D to L clearly indicates that stacking of side chains occurs.