bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Addition Reactions of 1,3‐Thiazole‐5(4H)‐thione Oxides
Authors: Shi Junxing , Tromm Peter , Heimgartner Heinz 
Published: December 2004

Abstract1,3‐Thiazole‐5(4H)‐thione oxides 2 were prepared by oxidation of the corresponding 1,3‐thiazole‐5(4H)‐thiones 1 with m‐chloroperbenzoic acid (Table 1). Addition reactions of 2 with organolithium and Grignard reagents yielded 4,5‐dihydro‐4,4‐dimethyl‐1,3‐thiazol‐5‐yl methyl sulfoxides of type 4 via thiophilic attack (Table 2). Whereas the reaction with the organolithium compounds proceeded with fair‐to‐excellent yields, the Grignard reagents reacted only very sluggishly. The sulfoxides 4 could also be prepared via oxidation of 4,5‐dihydro‐4,4‐dimethyl‐5‐(methylthio)‐1,3‐thiazoles of type 3 with m‐chloroperbenzoic acid, together with the corresponding sulfones 5 (Scheme 1).
Multiorganyltin Compounds. Designing a novel phosphate‐selective carrier
Authors: Tsagatakis John K. , Chaniotakis Nikolas A. , Jurkschat Klaus 
Published: December 2004

AbstractA series of distannyl derivatives, 1–9, were studied for their application as phosphate‐selective carriers in polymer‐based liquid membranes. A drastically different potentiometric behavior was observed depending on the distance between the tin(IV) coordinating centers and the ligands attached to them. Some of the compounds examined, i.e. (PhSnBr2)2CH2(1) and (Me3SiCH2SnCl2CH2)2 (3) showed very high potentiometric selectivity towards phosphate over other lipophilic anions such as perchlorate and thiocyanate. Results indicate that (1) the optimal number of CH2 groups between the Sn‐centers are either one or three, (2) the electron‐withdrawing power of the organic ligands attached to Sn‐centers strongly influences the overall response towards phosphate, and (3) the steric effect of the organic substituents is important in the potentiometric selectivity observed.
Conformational Parameters of the Sandalwood‐Odor Activity: Conformational calculations on sandalwood odor
Authors: Buchbauer Gerhard , Hillisch Alexander , Mraz Karin , Wolschann Peter 
Published: December 2004

AbstractThe conformational parameters responsible for sandalwood odor were investigated by the “active‐analog approach”. The pharmacophoric (osmophoric) pattern of sandalwood‐odor molecules can be outlined as three points: the OH group (point PI), a lipophilic group (point P2) 2.9–3.0 Å distant from the OH group, and a bulky rigid group (point P3), represented as a dummy atom in the middle of the alicyclic system (norbornane bicycle or cyclopentene ring) or a quaternary C‐atom. This concept was tested on a series of representative sandalwood‐odor compounds and on some structurally similar, but odorless substances.
Cyclopropanization of Methyl Carboxylates with Tebbe‐Type Reagents
Authors: Fallahpour Reza‐Ali , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe methylenation reaction of methyl azulene‐2‐carboxylates (cf. Schemes 1 and 2) with Tebbe's or Takai's reagent is described. When the prescribed amount of Takai's reagent is applied in a four‐fold excess, the corresponding cyclopropyl methyl ethers are formed instead of the enol ethers (cf. Schemes 2 and 3). Similarly, methyl benzoate and methyl 2‐naphthoate yield, after treatment with Takai's reagent and hydrolysis, the corresponding cyclopropanols 18 and 19, respectively (Scheme 3). The cyclopropyl methyl ether 4 or cyclopropanol 5 rearrange, on acid catalysis, into the l‐(azulen‐2‐yl)propan‐l‐one 20 (Scheme 4). whose reduction with Et3SiH in CF3COOH yields the 2‐propylazulene 21.
Structure‐Lipophilicity and Structure‐Polarity relationships of amino acids and peptides
Authors: Vallat Philippe , Gaillard Patrick , Carrupt Pierre‐Alain , Tsai Ruey‐Shiuan , Testa Bernard 
Published: December 2004

AbstractThe objectives of this study were to gain insights into the structure‐lipophilicity relationships of peptides and to propose an improved model for estimating their lipophilicity. First, existing databases were extended to obtain the distribution coefficients of a total of 208 free or protected peptides (di‐ to pentapeptides). The polarity parameters (Λ) of 23 free amino acids and 19 protected amino acids (AcNHCHRCONH2) and of their side chains were calculated from experimental distribution coefficients and computed molecular volumes. An analysis of the polarity parameters revealed that the hydrophobicity of the amino‐acid side chains is largely reduced due to the polar field of the backbone. The polarity parameters of the peptides were then obtained in a similar manner and shown to be highly correlated with the sum of the polarity parameters of their side chains, i.e., the lipophilicity of peptides can be calculated from their molecular volume and the sum of their side‐chain polarities using the regression established for each individual series of peptides (Fig. 1). This last restriction is essential since the polarity and lipophilic increment of a NHC*HCO unit were shown to decrease with increasing length of backbone.
Oligosaccharides related to tumor‐associate antigens. Part 3. Synthesis of the propyl glycosides of the trisaccharide β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc‐(1→3)‐α‐D‐Galp and of the Tetrasaccharide α‐L‐Fucp‐(1→2)‐β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc‐(1→3)‐α‐D‐Galp, components of a tumor antigen recognized by the antibody MBr1
Authors: Lay Luigi , Panza Luigi , Russo Giovanni , Colombo Diego , Ronchetti Fiamma , Adobati Elena , Canevari Silvana 
Published: December 2004

AbstractThe synthesis of the trisaccharide β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc‐(1→3)‐α‐D‐Galp‐1‐OPr (2) and of the tetrasaccharide α‐L‐Fucp‐(1→2)‐β‐D‐GalpNAc‐(1→3)‐β‐D‐Galp‐1‐OPr (3), starting from the disaccharidic dihydrooxazole donor 5, is described. Glycosylation of 5 with 6 in the presence of Me3SiOTf gave the trisaccharide 7 which was deprotected with standard methods to give, via 8, compound 2 (Scheme 1). Alternatively, protection of 8 as the 4′,6′‐O‐benzylidene derivative 9 followed by glycosylation with 10 and by standard deprotection afforded the tetrasaccharide 3 (Scheme 2). Biological testing showed that trisaccharide 2 is unable to inhibit the binding of the monoclonal antibody MBr1 to the target tumor cells MCF7, while tetrasaccharide 3 inhibits the binding in ca. 7‐fold extent with respect to the previously tested trisaccharide α‐L‐Fucp‐(1→2)‐β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc‐1‐OPr. These results indicate that the galactose corresponding to the unit D of compound 1 plays an important role in defining the MBr1‐recognized epitope and confirm the essential role of fucose for MAb recognition.
Oligosaccharides Related to Tumor‐Associate Antigens. Part 4. Modeling of the terminal tetrasaccharide of an antigen recognized by the MBr1 antibody and of overlapping Di‐ and trisaccharide sequences
Authors: Toma Lucio , Colombo Diego , Ronchetti Fiamma , Panza Luigi , Russo Giovanni 
Published: December 2004

AbstractThe conformational space of the tetrasaccharide α‐L‐Fuc‐(1→2)‐β‐D‐Gal‐(1→3)‐β‐D‐GalNAc‐(1→3)‐α‐D‐GallPr (3) and of some overlapping di‐ and trisaccharide sequences was investigated with the aid of molecular‐mechanics energy minimizations, molecular‐dynamics simulations, and 1H‐NMR analysis. These investigations suggested that in compound 3 a certain rigidity of the first two glycosidic linkages (Fuc‐Gal and Gal‐GalNAc) is combined with the flexibility of the third one (GalNAc‐Gal).
Synthesis, Structure, and Antimalarial Activity of Some Enantiomerically Pure, cis‐fused cyclopenteno‐1,2,4‐trioxanes
Authors: Jefford Charles W. , Kohmoto Shigeo , Jaggi Danielle , Timári Géza , Rossier Jean‐Claude , Rudaz Manyck , Barbuzzi Olivier , Gérard David , Burger Ulrich , Kamalaprija Philippe , Mareda Jiri , Bernardinelli Gérald , Manzanares Ignacio , Canfield Craig J. , Feck Suzanne L. , Robinson Brain L. , Peters Wallace 
Published: December 2004

AbstractTwo pairs of enantiomerically pure cis‐fused cyclopenteno‐1,2,4‐trioxanes (7, ent‐7 and 8, ent‐8) are prepared (Schemes 1–3). Their identities are established by dye‐sensitized photo‐oxygenation of ent‐7 and 8, ent‐8 to the allylichydroperxides, reduction to the corresponding alcohols, and conversion to the (1S)‐camphanates (Scheme 4), the structures of which are determined by X‐ray analysis. The dynamic properties of ent‐7 are investigated by NMR spectroscopy and PM3 calculations. Evidence for an easily accessible twist‐boat conformation is obtained. The in vitro and in vivo antimalarial activities of 7, ent‐7,8, and ent‐8 as well as those of the racemic mixtures are evaluated against Plasmodium falciparum, P. berghei, and P. yoelii. No correlation is observed between configuration and activity. Racemates and pure enantiomers have commensurate activities. The mode of action on the intraerythrocytic parasite is rationalized in terms of close docking by the twist‐boat conformer of the trioxane on the surface of a molecule of heme, single‐electron transfer to the OO σ* orbital, and scission to the acetal radical which then irreversibly isomerizes to a C‐centered radical, the ultimate lethal agent (Scheme 5).
Synthesis of (±)‐Pyrenolide B
Authors: Moricz Attila , Gassmann Elisabeth , Bienz Stefan , Hesse Manfred 
Published: December 2004

AbstractIn the synthesis of the title compound 12, the important intermediate 7 was obtained in good yield from the easily available ethyl 5, 5‐ethylenedioxy‐2‐oxocyclohexane‐1‐carboxylate (1) via ring enlargement of the bicyclic enol ether 5 (Scheme). Its reduction (NaBH4 in EtOH) and subsequent protection with (t‐Bu)Me2Si resulted in the highly functionalized ten‐membered lactone 9. Introduction of the (Z)‐configurated double bond, followed by deprotection and elimination of H2O, gave (±)‐pyrenolide B (12) in 16% overall yield.
O‐(1‐Phenyl‐1H‐tetrazol‐5‐yl) Glycosides: Alternative synthesis and transformation into glycosyl fluorides
Authors: Palme Monica , Vasella Andrea 
Published: December 2004

AbstractA number of new glycosyl donors, O‐(1‐phenyl‐1H‐tetrazol‐5‐yl) glycosides, are prepared from the corresponding hemiacetals, commercially available 5‐chloro‐1‐phenyl‐1H‐tetrazole (2), and tetrabutylammonium fluoride (Bu4NF) in either THF or DMF. The mild reaction conditions are compatible with a variety of protecting groups. The glycosyl donors are treated with hydrogen fluoride‐pyridine complex (HF·py) to rapidly provide glycosyl fluorides in good‐to‐excellent yields, apparently by a (single or double) SN2 mechanism as studied by both 1H‐ and 19F‐NMR spectroscopy. Under acidic conditions, glycosyl fluorides equilibrate partially or completely, equilibration requiring a large excess of HF · py.
Calculating the Thermodynamics of Weakly Hydrogen‐Bonded Complexes from Heteronuclear NMR Data: Base‐pairing stabilities of a 5‐methyl(15N2)[O2, O4‐17O2]uridine (= (15N2)[O2,O4‐17O2]ribosylthymine) derivative, and structural implications
Authors: Strazewski Peter 
Published: December 2004

Abstract2′,3′‐O‐Isopropylidene‐5‐methyl(15N2)[O2,O4‐17O2]uridine (= 2′,3′‐O‐isopropylidene (15N2)[O2,O4‐17O2]‐ribosylthymine; 1) was analyzed by 15N‐and 17O‐NMR spectroscopy. The 15N and 17O chemical shifts revealed, in the absence and presence of unlabelled 2′,3′‐O‐isopropylideneadenosine (2), the formation of thymine‐thymine and thymine‐adenine base pairs in CHCl3. As expected, cyclic complexes stabilized by two H‐bonds occurred at low temperatures, but at elevated temperatures, the data suggest that open complexes involving only one H‐bond prevailed. The 17O‐NMR data showed the cyclic thymine‐adenine pair in a reverse base pair geometry. The open base pair involved contacts to the urea‐derived carbonyl O‐atom of thymine. The thermodynamics of complex formation of the cyclic and open forms in both homo and hetero pairs were calculated from the temperature and concentration dependence of the 15N‐NMR data using a new method. It involves a fitting procedure onto the experimental isotherms using a theoretically derived function with the standard Gibbs free energy as a parameter to be optimized. ΔH° and ΔS° were derived from a linear regression of ΔG°(T) vs. T. The fitting procedure circumvents the baseline problem and could be automated and used to calculate correct thermodynamics from UV‐monitored melting curves of oligonucleotides. Since titrations are not involved, this dilution method should also be a useful alternative for stability studies of supramolecular complexes in H2O and in organic solvents.
Crystal Smectic‐B Phase from a Mesomorphic Ferrocene Derivative
Authors: Deschenaux Robert , Marendaz Jean‐Luc , Santiago Julio , Goodby John W. 
Published: December 2004

AbstractThe thermal properties of two ferrocene derivatives, substituted by either one or two cholesteryloxycarbonyl units, were investigated. While the monosubstituted ferrocene derivative 1 was found to be non‐mesomorphic, the disubstituted ferrocene derivative 2 exhibited a crystal smectic‐B phase. This result shows that ferrocene‐containing thermotropic liquid crystals, despite the bulkiness of the metallocene core, are not limited to disordered calamitic phases.
Synthesis, Structure, and Reactivity of Secosteroids Containing a Medium‐Sized Ring. Part 36. Transannular photocyclization of some unsaturated 5,10‐secosteroidal ketones: A reevaluation
Authors: Heckendorn Roland , Fuhrer Hermann , Kalvoda Jaroslav , Lorenc Ljubinka , Pavlović Vladimir , Mihailović Mihailo Lj. 
Published: December 2004

AbstractThe structures 9 and 8 are proposed for the single isolated irradiation product of 5‐oxo‐5,10‐secocholest‐1(10)‐en‐3α‐yl acetate (6) [2] and for the minor product of irradiation of 5‐oxo‐5,10‐secocholest‐1(10)‐en‐3β‐yl acetate (1) [3], respectively. These compounds are formed in an alternative reaction with respect to the originally observed intramolecular Paterro‐Büchi photoprocess (transformation of 1 to oxetane 2). The formerly postulated ‘active’ conformations for 1 and 6 still allow explanation of their generation.
Short, Enantiospecific Syntheses of Indolizidines 209B and 209D, and Piclavine A from Diethyl‐L‐Glutamate
Authors: Jefford Charles W. , Sienkiewicz Krzysztof , Thornton Steven R. 
Published: December 2004

AbstractThe 1H‐pyrrole derivative obtained from diethyl L‐glutamate hydrochloride and tetrahydro‐2,5‐dimethoxyfuran was cyclized with BBr3 to ethyl (5S)‐5,6,7,8‐tetrahydro‐8‐oxoindolizine‐5‐carboxylate (18). Catalytic hydrogenation of 18 over Pd/C in AcOH gave ethyl (5S,8aR)‐octahydroindolizine‐5‐carboxylate (21), whereas hydrogenation over Rh/Al2O3 in EtOH/AcOH 99:1 afforded mainly ethyl (5S,8S,8aS)‐octahydro‐8‐hydroxyindolizine‐5‐carboxylate (22). By functional‐group interconversions, 21 was transformed into piclavine A (1) and indolizidine 209D (2). Similarly, (5R,8R,8aS)‐octahydro‐5‐pentylindolizine‐8‐methanol (37), the final relay for indolizidine 209B (3), was obtained from 22.
Reassignment of the Configuration of Several Keto‐cyclolignans Prepared from Podophyllotoxin
Authors: Miguel del Corral José María , Gordaliza Marina , López José‐Luis , Olmo Esther Del , Angeles Castro M. , Luisa López M. 
Published: December 2004

AbstractThe configuration of several keto‐cyclolignans related to podophyllotoxin has been reviewed. Under basic catalysis, the configuration at the C‐atom in α‐position to the lactone carbonyl group in podophyllotoxone is inverted instead of the C‐atom in α‐position to the ketone group, as it has been reported.
Syntheses and PE‐Spectroscopic Investigations of 2,6‐ and 3,5‐Bridged 1,4‐Dimethylidenecyclohexanes
Authors: Chou Teh‐Chang , Lange Holger , Gleiter Rolf , Gögh Tibor , Kríž Miroslav , Pfenninger Max H. , Valentíny Marian , Ganter Camille 
Published: December 2004

AbstractThree 1,4‐dimethylidenecyclohexanes, bridged in the 2,6‐ and 3,5‐positions by two ethano (4), one ethano and one propano (5), and two propano bridges (6) have been synthesized. The interaction of the two exocyclic methylidene groups has been investigated by He(I) photoelectron (PE) spectroscopy. It revealed a slightly larger energy difference (0.8 eV) for 4 and 5 as compared to the parent 1,4‐dimethylidenecyclohexane (7) (0.7 eV). The interpretation of the PE spectra was based on the comparison with PE data of related systems and with the results of semiempirical calculations on 4–6.
Oligosaccharide Analogues of Polysaccharides. Part 5. Studies on the cross‐coupling of alkynes and haloalkynes
Authors: Cai Chengzhi , Vasella Andrea 
Published: December 2004

AbstractThe cross‐coupling of the homopropargylic ether 1 and the halopropargylic ethers 2a and 2b was optimized, and aspects of the coupling mechanism were studied. Coupling promoted by Pd° and Cu1 in the presence of an amine yielded a mixture of the heterodimer 3 and the homodimers 4 and 5 (Scheme 1). Optimizations were first directed at suppressing homo‐coupling. Homo‐coupling is partially due to a H/I exchange (1 + 2a ⇌ 6 + 7) promoted by CuI and an amine. The exchange, but not the formation of homodimers, was largely suppressed in DMSO. The influence of phosphine ligands was also evaluated. Weaker σ‐donors (with the exception of PPh3) lead to a faster coupling and to a higher ratio of hetero‐ to homodimers, with P(fur)3 leading to the cleanest reaction. Homodimers are also formed (together with I2 · (i‐Pr)2NH) by reductive dimerization of the iodoalkyne 2a in the presence of [Pd2(dba)3], CuI, and (i‐Pr)2NH. Bulky and acceptor‐substituted amines reduced the extent of the dimerization of 2a, but the bulkiest amines did not promote coupling. Better results were obtained by using the bromoalkyne 2b. Neither dimerization of 2b, nor H/Br exchange between 1 and 2b were observed. Coupling of 1 and 2b was slower than the one of 1 and 2a, but gave higher yields of the heterodimer 3. The yield of 3 and the ratio of hetero‐to homodimers was greatly improved by addition of LiI; no phosphine ligand is then required. While the oxidative addition of the iodoalkyne 2a to [Pd(PPh3)4] (2a → 8a) was rapid, the one of the bromoalkyne 2b was much slower and proceeded via the η2‐complex 9 as evidenced by 1H‐NMR spectroscopy. The rearrangement of 9 to the bromopalladium σ‐complex 8b follows first‐order kinetics (k = 0.014 min−1). CuBr greatly increased the rate of this rearrangement. LiI caused rapid substitution of Br by I in the Pd σ‐complex (8b → 8a), but not in 9, nor in 2b. The σ‐complex 8a did not react with the alkyne 1 in the presence of (i‐Pr)2NH, unless CuI was added. The alkynes 10 or 1 did not react with CuI and either TMEDA or (i‐Pr)2NH to yield detectable amounts of the Cu‐acetylides 11 or 12. These observations are rationalized by the mechanism shown in Scheme 3, postulating the intermediacy of the binuclear alkyne‐Pd‐Cu complexes C and J, and some or all of E–H, and highlighting the role of CuI in this coupling.
A 1H‐NMR Spectroscopic Investigation of the Conformation of the Acetamido Group in Some Derivatives of N‐Acetyl‐D‐allosamine and ‐D‐glucosamine
Authors: Fowler Paul , Bernet Bruno , Vasella Andrea 
Published: December 2004

AbstractThe population of the conformations obtained by rotation around the C(2)N and the NC(O) bonds of AllNAc, GlcNAc, and GlcNMeAc derivatives was investigated by 1H‐NMR spectroscopy. The AllNAc‐derived α‐D‐and β‐D‐pyranosides 4–7, the AllNAc diazirine 16, and the GlcNAc‐derived axial anomers α‐D‐8–10 prefer the (Z)‐anti‐conformation. A significant population of the (Z)‐syn‐conformer in the (Z)‐syn/(Z)‐anti‐equilibrium for the equatorial anomers β‐D‐8–10 and the GlcNAc diazirine 17 was evidenced by an upfield shift of HC(2), downfield shifts of HC(1) and HC(3), and by NOE measurements. The population of the (Z)‐syn‐conformation depends on the substituent at C(1) and is highest for the hexafluoroisopropyl glycoside. The population of the (Z)‐syn‐conformation of β‐D‐14 decreases with increasing polarity of the solvent, but a substantial population is still observed for solutions in D2O. Whereas the α‐D‐anomers of the hemiacetal 22 and the methyl glycoside 21 prefer the (Z)‐anti‐conformation in D2O solution, the corresponding β‐D‐anomers are mixtures of the (Z)‐anti‐and (Z)‐syn‐conformers. The diazirine 17 self‐associates in CD2Cl2 solution at concentrations above 0.005M at low temperatures. The axial anomers of the GlcNMeAc derivatives α‐D‐26–28 are 2:1 to 3:1 mixtures of (Z)‐anti‐and (E)‐anti‐conformers, whereas the corresponding β‐D‐glycosides are ca. 1:3:6 mixtures of (Z)‐syn‐, (Z)‐anti‐, and (E)‐anti‐conformers.
Novel Thiazole‐Containing Complexing Agents and Luminescence of Their Europum(III) and Terbium(III) Chelates
Authors: Mukkala Veli‐Matti , Liitti Päivi , Hemmilä Ilkka , Takalo Harri , Matachescu Cristina , Kankare Jouko 
Published: December 2004

AbstractThe synthesis of novel thiazole‐containing complexing agents and their luminescence properties with EuIII and TbIII ions are reported. One of these terpyridine analogues was also tested as an EuIII labelling reagent, and its luminescence properties as an antibody conjugate were studied.
Kinetics and Mechanisms of Racemization: 5‐Substituted Hydantoins (= Imidazolidine‐2,4‐diones) as Models of Chiral Drugs
Authors: Reist Marianne , Carrupt Pierre‐Alain , Testa Bernard , Lehmann Søren , Hansen Jan Jørn 
Published: December 2004

AbstractA chiral center in a drug molecule increases the complexity of synthetic, metabolic, pharmacological, and clinical studies, an additional problem being a possible lack of configurational stability. Here, we report detailed kinetic and mechanistic studies on the deuteration and racemization of seven 5‐monosubstituted hydantions (= imidazolidine‐2,4‐diones) used as model compounds. Using 1H‐NMR and chiral RP‐HPLC, rates of reaction and thermodynamic parameters of activation were determined for the reactions of deuteration and racemization. Energies of deprotonation were obtained by molecular‐orbital calculations performed at the AM1 level. It is demonstrated that the deuteration and racemization of 5‐monosubstituted hydantoins follow general‐base catalysis. The identical (within experimental errors) activation energies of deuteration and racemization indicate that the two reactions share a common reaction mechanism. The fact that the pseudo‐first‐order rate constants of deuteration are about half of those of racemization suggests that deuteration occurs with inversion of configuration. Very large differences in reaction rates were observed between the seven compounds, indicating the marked influence of substituents on chiral stability. These results, together with the small isotope effects observed, and the comparison between experimental activation energies and calculated energies of deprotonation, suggest a SE2 push‐pull mechanism for the racemization of 5‐monosubstituted hydantoins.
Trinuclear Double Helicates of Iron(II) and Nickel(II): Self‐assembly and resolution into helical enantiomers
Authors: Hasenknopf Bernold , Lehn Jean‐Marie 
Published: December 2004

AbstractThe synthesis of the linear tris[terpyridine] 1 with three tridentate binding sites is described. The reaction with metal ions of octahedral coordination geometry, such as FeII or NiII, leads to the self‐assembly of trinuclear complexes [M3(1)2]6+, which display properties in agreement with a double helical structure. The trinuclear iron (II) helicate has been resolved into its enantiomers.