Radioracemization and radiation-induced chiral amplification of chiral terpenes measured by optical rotatory dispersion (ORD) spectroscopy

For the first time the radioracemization of α(+)pinene and α(−)pinene, of turpentine and of R(−)-α-phellandrene has been studied by optical rotatory dispersion (ORD) spectroscopy. For all these compounds, the radioracemization implies a shift of the ORD curves toward lower levels of specific optical rotation. The radioracemization degree (R_R) has been defined and calculated for all the compounds studied. It has been found that for radiation dose of 1 MGy the radioracemization degree is about 4.5% for the compound with the highest optical purity and reaches 7–8% for the less optically pure compounds, demonstrating that impurities can affect greatly the radioracemization.In contrast with the general radioracemization effect exerted by high-energy radiation on chiral molecules, β(−)pinene, β(+)pinene when irradiated show an increment of their specific optical rotation. This fact has been measured for the first time by ORD spectroscopy and the amplification degree of chirality can reach 1000% in the near UV. This phenomenon is due to the formation of a chiral polymer, poly-β-pinene, which forms a solution with the monomer enhancing its optical activity. The implications for the theories of the origin of life of such unexpected phenomenon are discussed briefly.     

Asymmetric selective copolymerization of propylene oxide with d-camphoric acid anhydride

The ring-opening copolymerization of propylene oxide with d-camphoric acid anhydride [α]_D ?3.4° was carried out with diethylzinc and triethylamine as catalysts. It was found that the products were alternating copolymers which were optically active. The optical rotatory dispersion curves were found to fit a simple Drude equation having a λ_c value of 201 mμ. The specific rotation increased with increasing intrinsic viscosity of the product. The propylene oxide recovered from the polymerization system was optically active. Its specific rotation increased with increasing polymerization time. It is thought that the asymmetric selective copolymerization of propylene oxide is caused by the influence of the optically active camphoryl group of the polymer end.     

General approach for the total synthesis of the sarpagine related indole alkaloids (+)-Na-methyl-16-epipericyclivine, (−)-alkaloid Q3 and (−)-panarine via the asymmetric Pictet-Spengler reaction

The stereospecific total synthesis of (+)-N_a-methyl-16-epipericyclivine (1) was completed [from d-(+)-tryptophan methyl ester] in an overall yield of 42% (eight reaction vessels). The optical rotation {[α]_D +22.8 (c 0.50, CHCl₃)} obtained on this material confirmed that the reported optical rotation {[α]_D 0 (c 0.50, CHCl₃)} [] was biogenetically unreasonable. The first total synthesis of (−)-alkaloid Q₃ (5) and (−)-panarine (6), via the intermediate vellosimine (18), is also described.     

Optically active cyclic poly(ether sulfone)s based on chiral 1,1′-bi-2-naphthol

Optically active cyclic poly(ether sulfone)s are prepared from 4-fluorophenyl sulfone and (R)- or (S)-1,1′-bi-2-naphthol. The measurement of MALDI-TOF MS shows that the product is composed of a series of cyclic and linear oligomers where the repeating unit number (n) is from 2 to 12, from which the cyclic dimers (n=2), and cyclic trimer (n=3) have been separated from their homologous compounds by TLC successfully. Specific optical rotation [α]_D²⁵ is −583.0 for (R)-cyclic dimer, +588.0 for (S)-cyclic dimer, +22.7 for (R)-cyclic trimer, and −20.3 for (S)-cyclic trimer. Their properties are also determined by other methods, such as ¹H NMR and CD etc.     

Measurement of molecular mass of chitosan oligomers

The molecular mass of chitosan oligomers in the range of (2-5) × 10³ was measured using viscometry and gel permeation chromatography. The use of viscometers with a flow time of at least 108 s (0.33 M CH₃COOH + 0.3 M NaCl as a solvent, 21°C, [η] = 3.41M ^1.02) makes it possible to determine the molecular mass of chitosan oligomers up to 1.98 × 10³. In this case, the maximum divergence in the molecular mass values of oligomers determined by viscometry and gel permeation chromatography does not exceed 4%.     

Synthetically defined oligomers ofL-lysine as model compounds for adsorption studies

For investigations of adsorption of polymers onto surfaces, lysine oligomers of defined lengths were synthesized using standard methods of peptide chemistry. By repeated coupling of peptide derivatives of the same length, peptide chains up to 32 lysine residues were obtained. To suppress end effects theN-terminalα-amino group and the carboxyl group of each peptide were blocked with?-aminocaproyl- andN-methylamide functions respectively. Measurements of the optical rotation of blocked and charged deblocked oligo-L-lysines indicated that ordered structures are present in both forms.     

Synthesis and properties of stereoregular 2,3,4-tri-o-acetyl-[1 → 6]-α-D-gluco-, -manno-, and -galactopyranans

Polymerization 1,6-anhydro-2,3,4-tri-O-benzyl-β-D -mannopyranose at ?60°C with phosphorus pentafluoride (0.9 mole-%) gives stereoregular 2,3,4-tri-O-benzyl-[1 → 6]-α-D -mannopyranan with substantially higher viscosity ([η] = 2.8 dl/g) than the corresponding gluco- and glactopyranan derivatives prepared similarly. Debenzylation with sodium in liquid ammonia produces stereoregular [1 → 6]-α-D -mannopyranan of viscosity up to [η] = 0.54 dl/g. Stereoregular 2,3,4-tri-O-acetyl-[1 → 6]-α-D -glycopyranans are most simply prepared by acetylation of the corresponding crude [1 → 6]-α-D -glycopyranans obtained directly from the debenzylation reaction. The galactan is extremely difficult to acetylate by conventional methods if isolated in a pure form. Physical and spectral properties of these highly stereoregular synthetic 2,3,4-tri-O-acetyl-[1 → 6]-α-D -glycopyranans are presented. Optical rotary dispersion curves of 2,3,4, tri-O-acetyl-[1 → 6]-α-D -glycopyranans show small Cotton effects in the 200–230 nm region, superimposed on strong background rotation. Circular dichroism spectra show a single n →^* acetate absorption band for each polymer. The sign of the band appears to be determined largely by the C-2 configuration. Stereoregular 2,3,4-tri-O-acetyl-[1 → 6]-α-D -glycopyranans in 2,2,2-trifluoroethanol solution are likely to possess a random rather than helical conformation.     

Synthesis and biological activity of both (E)- and (Z)-isomers of optically pure (S)-14-methyl-8-hexadecenal (trogodermal), the antipodes of the pheromone of the khapra beetle

Both (E)- and (Z)-isomers of (S)-14-methyl-8-hexadecenal (trogodermal) were synthesized from 100% optically pure (R)-(+)-citronellic acid. These antipodes of the khapra beetle pheromone were 1/500 to 1/1000 times as active as the natural (R)-pheromone. Determination of the optical purities of citronellic acid and related compounds was achieved by hplc method. Warning was made not to forget the measurement of density in expressing the optical rotation of a neat liquid as [α]_D (neat).     

Birefringence induite dans les directions remarquables d'une suspension de particules rigides en ecoulement

A theoretical formula is derived for the flow birefringence exhibited along the streamlines and in the direction of the shear rate (G) by dilute suspensions of rigid spheroid-like macromolecules; numerical values are computed up to σ = G/D = 900 (D = rotary diffusion coefficient). These results provide two tests for identifying prolate and oblate particles; when combined with the data for observation perpendicular to the plane of flow, they confirm the connection between non-Newtonian viscosity and the Maxwell effect for monodisperse samples; for vanishing rate of shear, they allow a mixture of particles to be characterized by means of a mean rotary diffusion constant ($\text{D}$) and a mean shape coefficient ($\text{R}$).     

ORD and CD studies of poly[(S)(−)-N-α-methylbenzylethylenimine]

The advantages of chiral N-substituted polyethylenimines for the chiroptical study of macromolecular conformations in solution have been considered. Poly[(S)(?)-N-α-methylbenzylethylenimine] (poly-3) and five model compounds have been obtained and their chiroptical properties studied. The cyclic dimer and tetramer of imine 3 are suitable models for the chiroptical study of configurational and conformational behaviour of randomly coiled and helical poly-3 in solution. Unlike the disordered poly-3 in acidified solvents and the configurational models in various solvents, helical poly-3 in hydrocarbon solvents has positive optical rotation and positive CD-band of the tertiary amine chromophore at 223 nm. The appearance of this inherently chiral chromophore of the helix explains the observed changes of the sign and values of the optical rotation of poly-3 in various solvents which are mainly caused by conformational transformations of the main chain. The presence of helical conformations of poly-3 in solution are also confirmed by optical rotation data of stereocopolymers and the concentration dependence data of ORD curves of poly-3. This conclusion agrees with NMR and i.r.-data.     

Asymmetric radical polymerization of butadiene 1-carboxylic acid

Optically active S(?)-α-phenethylammonium butadiene 1-carboxylate was prepared and polymerized in methanol, using azobisisobutyronitrile as initiator. The optical rotation, optical rotatory dispersion and circular dichroism spectra of the polymers, before and after removal of chiral amine, have demonstrated that the asymmetric induction occurred in the main chain. An asymmetric inductive polymerization mechanism is discussed.     

Radiation Chemical Studies of Protein Reactions: Effect of Post-irradiation on Optical Rotation

When protein was irradiated by γ-rays from a ⁶⁰Co source, a post-irradiation effect of protein reaction was caused. An empirical equation for the optical rotation was obtained, and the phenomena were explained on the basis of the molecular mechanism. The general equation for the optical rotation is given by [α] f= a ? b log t, where [α] f is the final specific rotation of the solution, t is time after γ irradiation, and a and b are adjustable constants.     

Evaluation of matrix-assisted laser desorption ionization mass spectrometry for polymer characterization

A protocol for the preparation of polymeric samples for time-of-flight matrix-assisted laser desorption ionization mass spectrometry (TOF-MALDI-MS) analysis was developed. Dithranol was identified as a good matrix for polystyrene (PS), and the addition of silver for cationization of molecules was determined to be necessary. Based on this preparative method, low molecular weight samples of other polymers [polyisoprene, polybutadiene, poly(ethylene oxide), poly(methyl methacrylate), and polydimethylsiloxane] were analyzed with molecular weights up to 49 ku. The effects of laser intensity were determined to influence the molecular weight distribution of intact oligomers, most significantly for low molecular weight polymers. Linear and reflectron modes of analysis were evaluated; better signal intensity and resolution were obtained in the reflectron mode. The TOF-MALDI-MS measurements are compared with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and gel permeation chromatography (GPC) for the same polymers. The M _n values calculated by TOF-MALDI-MS consistently are higher than values calculated by TOF-SIMS for all classes of polymers with molecular weights up to 8 ku. The molecular weights of the PS calculated from TOF-MALDI-MS are in good agreement with GPC (±10%). The composition of the terminal group on a polymer chain may affect the ion yields. The ion yields of intact oligomers were evaluated as a function of end group composition for both TOF-MALDI-MS and TOF-SIMS. The slight disparity of results between TOF-SIMS and TOF-MALDI-MS for the perfluoroalkyl-terminated PS suggests that the oligomers are desorbed preferentially from the surface in the TOF-SIMS analysis, rather than having an increased ionization probability.     

8,13-Epoxylabd-14-en-19-oic acid — A component of the needles ofPinus sylvestris

8,13-Epoxylabd-14-en-19-oic [(mannoyl oxide)-19-oic] acid, mp 64–66°C, [α]_D ?39.2° (c 1.0; ethanol) has been isolated from the needles ofPinus sylvestris. The following derivatives have been obtained: methyl 8,13-epoxylabd-14-en-19-oate, with mp 83–85°C, [α]_D ?43.2° (c 1.2; ethanol); 8,13-epoxylabd-14-en-19-ol, an oil, [α]_D ?10.9° (c 1.0; ethanol), n _D ²⁵ 1.5025, cyclohexylammonium salt with mp 113–115°C, [α]_D ?29.3° (c 1.0; ethanol); and 8,13-epoxydihydrolabd-14-en-19-oic acid with mp 61–63°C, [α]_D ?23.1° (c 1.0; ethanol). The structures of the compounds were established by IR, mass, PMR, and¹³C NMR spectroscopy.     

Peak parking method for measurement of molecular diffusivity in liquid phase systems

The combination of series of measurements of band broadening made with the peak parking (PP) method, using successively an open capillary tube and a HPLC column, gives a convenient procedure for the measurement of the molecular diffusivity (D_m) of compounds in solutions, of their axial dispersion coefficient (D_ax,m) in chromatographic columns, and of the tortuosity or obstructive factor of the column bed. The molecular diffusivity measured for benzene in methanol was in excellent agreement with literature data. The ratio of the axial dispersion coefficient to this diffusivity gives the obstructive factor (γ_m) of the packed bed, which was 0.74 for the column used. The values of D_m in other solutions were obtained from the D_ax,m values measured by the PP method, by correcting the D_ax,m values with the γ_m value. The D_m values determined by this method were in good agreement with those previously reported or estimated using literature correlations. These results showed that the PP method is effective for the experimental measurement of D_m.     

Polymerization of olefins catalyzed by a dichloride complex of titanium with a dioxolane dicarbonate ligand: The promoting effect of LiCl and MgCl2

The polymerizations of propylene and ethylene with two postmetallocene catalysts [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(perfluorophenyl)-1,3-dioxolane-4,5-dimethanol]TiCl₂ · MgCl₂ and [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra-(perfluorophenyl-1,3-dioxolane-4,5-dimethanol]TiCl₂· (LiCl)₂ are studied. The first catalyst shows higher activity in both reactions and forms a lower molecular mass PP. This PP is characterized by a wide molecular-mass distribution that can be described by a set of five or six Flory components with different average molecular masses. Along with heterogeneity with respect to kinetic parameters, there is heterogeneity with respect to stereospecificity. Some of the sites form a high-molecular-mass highly isotactic polymer whose melting point is ≥150°C, whereas other sites produce syndiotactic and atactic PPs. For the most isospecific sites, a stereocontrol mechanism similar to the mechanism typical for metallocene catalysts with C ₁-symmetry is advanced. The catalysts under study are composed of the [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(perfluorophenyl)-1,3-dioxolane-4,5-dimethanol]TiCl₂ complex supported on LiCl and MgCl₂, respectively.     

Asymmetric radiation-induced inclusion polymerization of 3-methyl-1,4-pentadiene in deoxycholic acid

The radiation-induced polymerization of 3-methyl-1,3-pentadiene (3MPD) as an inclusion complex in deoxycholic acid (DOCA) has produced in good yield the optically active polymer poly(3-methyl-1,4-pentadiene) (P3MPD) whose structure and properties were studied by FT-IR spectroscopy and thermal analysis (TGA, DTG and DTA). The data show that the polymer is essentially trans-1,4-P3MPD as expected for the polymerization in constrained media. Trans-1,4-P3MPD is optically active with [α]_D values comprised between +4.3 and +5.6. The optical rotatory dispersion curve of the P3MPD is completely different from that of DOCA as expected.     

Enantioseparation of doubly functionalized polar norbornenes by HPLC and their ruthenium‐catalyzed ring‐opening metathesis polymerization

Doubly fuctionalized polar norbornenes bearing the cyano and ester groups in 2,3‐positions are synthesized and enantiomers are separated by high performance liquid chromatography (HPLC) with a chiral stationary phase. These optically active monomers are polymerized by ruthenium carbene catalysts, and high yields of the polymers were obtained. The chiral monomer bearing ethyl ester gave an optically active polymer of lower, but opposite sign of optical rotation (monomer [α]_D = +61.0°, polymer [α]_D = ?3.1°). The circular dichroism (CD) of the obtained chiral polymers gave a Cotton effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 485–491, 2010     

An expedient and short synthesis of chiral α-hydrazinoesters: synthesis and conformational analysis of 1:1 [α/α-Nα-hydrazino]mers

Different α-hydrazinoesters with high optical purity have been obtained in large scale via an S_N2 protocol. A coupling reaction with a natural amino acid leads to the corresponding dimers, which have been oligomerized in order to obtain the 1:1 [α/α-N^α-hydrazino]mer series. Conformational studies show that these mixed oligomers are self-organized in solution via a succession of γ-turn and hydrazinoturn whatever the absolute configuration of the chiral carbons.     

Pd(II)‐catalyzed polymerization of optically active norbornene carboxylic acid esters

(?)‐(1S,2R)‐Norbornene‐2‐carboxylic acid alkyl esters (alkyl = Me, Bz, L ‐menthyl, or D ‐menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)‐(?)‐pantolactone‐O‐yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)‐based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]_D = ?24.7, polymer [α]_D = ?98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in ¹³C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006