Enantiomeric Polyketides from the Starfish‐Derived Symbiotic Fungus Penicillium sp. GGF16‐1‐2

One new racemic mixture, penicilliode A ( 1 ) and four pairs of enantiomeric polyketides, penicilliode B and C ( 2 and 3 ) and coniochaetone B and C ( 4 and 5 ), were obtained from the starfish‐derived symbiotic fungus Penicillium sp. GGF16‐1‐2. Interestingly, the strain GGF16‐1‐2 can produce enantiomers. The absolute configuration of 1 was determined by X‐ray diffraction (XRD) analysis, and the absolute configurations of 2 – 4 were determined by the optical rotation (OR) values and electronic circular dichroism (ECD) calculations. Compounds 1 – 5 were firstly isolated from the marine‐derived fungus Penicillium as racemates, and 2 – 5 were separated by HPLC with a chiral stationary phase. All the compounds were evaluated for their antibacterial, cytotoxic and inhibitory activities against PDE4D2.     

The determination of enantiomer composition of 1‐((3‐chlorophenyl)‐(phenyl)methyl) amine and 1‐((3‐chlorophenyl)(phenyl)‐methyl) urea (Galodif) by NMR spectroscopy,chiral HPLC,and polarimetry

For the first time, a method for enantiomer resolution of the anticonvulsant Galodif (1‐((3‐chlorophenyl)(phenyl)methyl) urea) by chiral HPLC was developed, whereas the enantiomeric composition of 1‐((3‐chlorophenyl)(phenyl)methyl) amine—precursor in Galodif synthesis—cannot be resolved by this method. However, starting 1‐((3‐chlorophenyl)(phenyl)methyl) amine quantitatively forms diastereomeric N‐((3‐chlorophenyl)(phenyl)methyl)‐1‐camphorsulfonamides in reaction with chiral (1R)‐(+)‐ or (1S)‐(?)‐camphor‐10‐sulfonyl chlorides. The diastereomeric ratio of obtained camphorsulfonamides can be easily determined by NMR ¹H and ¹³C spectroscopy. The DFT calculations of specific rotation of Galodif enantiomers showed good agreement with experimental data. The absolute configuration of enantiomers was proposed for the first time.     

Enantiomeric 4‐Acylamino‐6‐alkyloxy‐2 Alkylthiopyrimidines As Potential A3 Adenosine Receptor Antagonists: HPLC Chiral Resolution and Absolute Configuration Assignment by a Full Set of Chiroptical Spectroscopy

The chiral separation of enantiomeric couples of three potential A₃ adenosine receptor antagonists: (R/S)‐N‐(6‐(1‐phenylethoxy)‐2‐(propylthio)pyrimidin‐4‐yl)acetamide ( 1 ), (R/S)‐N‐(2‐(1‐phenylethylthio)‐6‐propoxypyrimidin‐4‐yl)acetamide ( 2 ), and (R/S)‐N‐(2‐(benzylthio)‐6‐sec‐butoxypyrimidin‐4‐yl)acetamide ( 3 ) was achieved by high‐performance liquid chromatography (HPLC). Three types of chiroptical spectroscopies, namely, optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD), were applied to enantiomeric compounds. Through comparison with Density Functional Theory (DFT) calculations, encompassing extensive conformational analysis, full assignment of the absolute configuration (AC) for the three sets of compounds was obtained. Chirality 28:434–440, 2016. © 2016 Wiley Periodicals, Inc.     

Theoretical and Molecular Docking Study of Ketoconazole on Heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin as Chiral Selector

A molecular docking study, using molecular mechanics calculations with AutoDock and semi‐empirical PM3 calculations, was used to predict the enantiodiscrimination of heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (TMβCD) and ketoconazole (KTZ) enantiomers. A Density Functional Theory (DFT) single‐point calculation at the level of B3LYP/6‐311G (d,p) was performed for the PM3‐optimized complexes to obtain more accurate binding energy and the electronic structures of the complexes. The difference in energies of the inclusion complexes between the KTZ enantiomers and TMβCD is probably a measure of chiral discrimination, which results in the separation of the enantiomers as observed in the experimental studies. Chirality 28:209–214, 2016. © 2015 Wiley Periodicals, Inc.     

Chiral Resolution and Absolute Configuration of the Enantiomers of the Psychoactive “Designer Drug” 3,4‐Methylenedioxypyrovalerone

Illicit rac‐MDPV (3,4‐methylenedioxypyrovalerone), manufactured in clandestine labs, has become widely abused for its cocaine‐like stimulant properties. It has recently been found as one of the toxic materials in the so‐called “bath salts,” producing, among other effects, psychosis and tachycardia in humans when introduced by any of the several routes of administration (e.g., intravenous, oral, etc.). The considerable toxicity of this “designer drug” probably resides in one of the enantiomers of the racemate. In order to obtain a sufficient amount of the enantiomers of rac‐MDPV to determine their activity, we improved the known synthesis of rac‐MDPV and found chemical resolving agents, (+)‐ and (–)‐2’‐bromotetranilic acid, that gave the MDPV enantiomers in >96% enantiomeric excess as determined by ¹H nuclear magnetic resonance and chiral high‐performance liquid chromatography. The absolute stereochemistry of these enantiomers was determined by single‐crystal X‐ray diffraction studies. Chirality 27:287‐293, 2015. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Organocatalytic alkylation of carbohydrate‐containing aldehydes with dihydroquinoline N,O‐acetals: Absolute configuration of 1,2‐dihydroquinolines

The direct catalytic α‐amidoalkylation of dihydroquinolines with aldehydes bearing oxygen functionalities at different positions in a Mannich‐type reaction has been studied. β‐Alkoxy‐aldehyde 1d gave high enantioselectivity, albeit with an inherently poor diastereoselectivity, while the use of α‐alkoxy aldehydes 1c was detrimental also to enantioselectivity. Mannich‐type reactions have been studied for the first time using new chiral carbohydrate‐derived aldehydes 1a,b showing a reactivity markedly influenced by the presence of water. The chiral glycidic backbone showed a slight but significant influence on the overall stereochemical outcome only when present in α‐position of the aldehyde. The absolute stereochemistry of the products was studied by electronic circular dichroism (ECD) spectra and compared with theoretical calculations. ECD analysis easily provides the absolute configuration of 1,2‐dihydroquinoline derivatives such as quinoline‐1(2H)‐carboxylates.     

Synthesis,HPLC Enantioresolution,and X‐ray Analysis of a New Series of C5‐methyl Pyridazines as N‐Formyl Peptide Receptor (FPR) Agonists

The synthesis of three racemates and the corresponding non‐chiral analogues of a C5‐methyl pyridazine series is described here, as well as the isolation of pure enantiomers and their absolute configuration assignment. In order to obtain optically active compounds, direct chromatographic methods of separation by HPLC‐UV were investigated using four chiral stationary phases (CSPs: Lux Amylose‐2, Lux Cellulose‐1, Lux Cellulose‐2 and Lux Cellulose‐3). The best resolution was achieved using amylose tris(5‐chloro‐2‐methylphenylcarbamate) (Lux Amylose‐2), and single enantiomers were isolated on a semipreparative scale with high enantiomeric excess, suitable for biological assays. The absolute configuration of optically active compounds was unequivocally established by X‐ray crystallographic analysis and comparative chiral HPLC‐UV profile. All compounds of the series were tested for formyl peptide receptor (FPR) agonist activity, and four were found to be active, with EC₅₀ values in the micromolar range. Chirality 25:400–408, 2013. © 2013 Wiley Periodicals, Inc.     

HPLC‐ECD and TDDFT‐ECD study of hexahydropyrrolo[1,2‐a]quinoline derivatives

Synthesis of racemic hexahydropyrrolo[1,2‐a]quinoline derivatives ( 1 ‐ 8 ) was performed by utilizing the Knoevenagel‐[1,5]‐hydride shift‐cyclization domino reaction. Separation of the enantiomers of the chiral products ( 1 ‐ 8 ) was carried out by chiral high‐performance liquid chromatography, and online high‐performance liquid chromatography‐electronic circular dichroism (ECD) spectra were recorded to elucidate the absolute configuration by comparing the experimental and time‐dependent density functional theory‐ECD spectra obtained at various theoretical levels. For 1 of the products, the time‐dependent density functional theory‐ECD calculations allowed determining both the relative and the absolute configuration by distinguishing the 4 stereoisomers. One of the compounds with spiro 1,3‐cyclohexanedione moiety ( 7 ) possessed moderate acetylcholinesterase inhibitory activity, while 3 showed neuroprotective activity in oxygen‐glucose deprivation‐induced neurotoxicity in human neuroblastoma SH‐SY5Y cells.     

Electronic Circular Dichroism of Chiral Alkenes: B3LYP and CAM‐B3LYP Calculations

Time‐dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) are widely used to determine absolute configurations (ACs) of chiral molecules. Two very popular DFT exchange‐correlation functionals, one hybrid (B3LYP) and one long‐range corrected (CAM‐B3LYP), along with a hierarchical sequence of basis sets were investigated, and the ECD spectra predicted for eight alkenes and compared to gas‐phase experimental spectra. Little variation in predicted ECD spectra was found with the basis set size enlargement, but the sensitivity to the functional is greater. Good agreement was obtained only with the CAM‐B3LYP functional, leading to the conclusion that TDDFT calculations of ECD spectra can routinely provide reliable ACs if and only if an appropriate functional is used. For camphene, twistene, syn‐(E)‐bisfenchylidene, and phyllocladene, solvent effects were estimated. Chirality 27:23–31, 2015. © 2014 Wiley Periodicals, Inc.     

Enantioselective σ1 receptor binding and biotransformation of the spirocyclic PET tracer 1′‐benzyl‐3‐(3‐fluoropropyl)‐3H‐spiro[[2]benzofuran‐1,4′‐piperidine]

It was shown that racemic (±)‐ 2 [1′‐benzyl‐3‐(3‐fluoropropyl)‐3H‐spiro[[2]benzofuran‐1,4′‐piperidine], WMS‐1813 ] represents a promising positron emission tomography (PET) tracer for the investigation of centrally located σ₁ receptors. To study the pharmacological activity of the enantiomers of 2 , a preparative HPLC separation of (R)‐2 and (S)‐2 was performed. The absolute configuration of the enantiomers was determined by CD‐spectroscopy together with theoretical calculations of the CD‐spectrum of a model compound. In receptor binding studies with the radioligand [³H]‐(+)‐pentazocine, (S)‐2 was thrice more potent than its (R)‐configured enantiomer (R)‐2 . The metabolic degradation of the more potent (S)‐enantiomer was considerably slower than the metabolism of (R)‐2 . The structures of the main metabolites of both enantiomers were elucidated by determination of the exact mass using an Orbitrap‐LC‐MS system. These experiments showed a stereoselective biotransformation of the enantiomers of 2 . Chirality, 2011. © 2010 Wiley‐Liss, Inc.     

Preparation and Studies of Chiral Stationary Phases Containing Enantiopure Acridino‐18‐Crown‐6 Ether Selectors

The enantiomeric separation ability of the newly prepared chiral stationary phases containing acridino‐18‐crown‐6 ether selectors was studied by high‐performance liquid chromatography (HPLC). The chiral stationary phases separated the enantiomers of selected protonated primary aralkylamines efficiently. The best results were found for the separation of the mixtures of enantiomers of NO₂‐PEA. Chirality 26:651–654, 2014. © 2014 Wiley Periodicals, Inc.     

Absolute Configuration Determination of Azulenyl Diols Isolated From Asymmetric Pinacol Coupling

A convenient enantioselective approach for the pinacol coupling of 1‐acetylazulene involving easily accessible (R)‐ or (S)‐BINOLs as chiral additive is reported. This supposes the preformation of the chiral titanium–BINOL complex in 1:2 ratio and subsequent reduction with zinc when, 2,3‐di(azulen‐1‐yl)butane‐2,3‐diol can be isolated in around 60% enantiomeric excess. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental and Boltzmann‐weighted calculated VCD and ECD spectra and assigned as (+)‐(2S;3S)‐di(azulen‐1‐yl)butane‐2,3‐diol. Chirality 27:826–834, 2015. © 2015 Wiley Periodicals, Inc.     

Synthesis,Chiroptical Properties and Density Functional Theory Calculations of 3,3’‐Biphenyl‐2,2’‐BiTropone

The synthesis of new bitropone derivatives, namely, 3,3'‐biphenyl‐2,2'‐bitropone and 7,7’‐biphenyl‐2,2'‐bitropone, are reported. Isolation of enantiomers arising from restricted rotation around the C‐C bond connecting the tropone moieties was attempted by means of chiral high performance liquid chromatography (HPLC). No separation was obtained for 7,7’‐biphenyl‐2,2'‐bitropone. For 3,3'‐biphenyl‐2,2'‐bitropone, difficulties were encountered because of the low separation factor of the peaks and the presence of a rapid racemization process. However, quantitative chiroptical data on the antipodes were obtained by linking a circular dichroism (CD) spectrometer and a UV–vis spectrophotometric detector in series to the HPLC instrument. The analysis of the CD and UV–vis spectra in terms of absolute conformations was done with the help of theoretical calculations performed at the Density Functional Theory (DFT) level. The most stable conformations of the 3,3'‐biphenyl‐2,2'‐bitropone in its ground state were obtained. Starting from these minimum energy conformations, it was possible to compute theoretical CD and UV absorption spectra that fit well with the experimental ones. From this comparison the absolute configuration to the antipodes was assigned. Finally, the effect of the presence of the two lateral phenyl substituents on the structure of the bitropone and hence on the CD spectrum is discussed. Chirality 25:648–655, 2013. © 2013 Wiley Periodicals, Inc.     

Axially chiral N‐(o‐aryl)‐4‐hydroxy‐2‐oxazolidinone derivatives from diastereoselective reduction of N‐(o‐aryl)‐2,4‐oxazolidinediones: Thermally interconvertible atropisomers via ring‐chain‐ring tautomerization

The reduction of the axially chiral N‐(o‐aryl)‐5,5‐dimethyl‐2,4‐oxazolidinediones by NaBH₄ yielded axially chiral N‐(o‐aryl)‐4‐hydroxy‐5,5‐dimethyl‐2‐oxazolidinone enantiomers having a chiral center at C‐4, with 100% diastereoselectivity as has been shown by their ¹H and ¹³C NMR spectra and by enantioselective HPLC analysis. The resolved enantiomeric isomers were found to interconvert thermally through an aldehyde intermediate formed upon ring cleavage via a latent ring‐chain‐ring tautomerization. It was found that the rate of enantiomerization depended on the size and the electronic effect of the ortho substituent present on the aryl ring bonded to the nitrogen of the heterocycle. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

Application of chiral technology in a pharmaceutical company. Enantiomeric separation and spectroscopic studies of key asymmetric intermediates using a combination of techniques. Phenylglycidols

Phenylglycidols substituted in the 2-, 3-, and 4- positions with fluorine, chlorine, and trifluoromethyl, and with methoxy in the 3- position, were synthesized from the corresponding E-cinnamic acids and separated into their (R,R)- and (S,S)- enantiomers using subcritical fluid chromatography with mixtures of MeOH in CO(2), on either a Chiralpak AD or AS chiral stationary phase. These compounds and commercially-available (R,R)- and (S,S)-phenylglycidol were analyzed for their vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotation (OR) properties to exemplify a strategy whereby the absolute stereochemistry of common and key chiral intermediates is established early in the structure-activity and structure-property relationship phase of a drug discovery program in a pharmaceutical company. From this study, substituents in the phenyl group of the synthesized molecules were found not to grossly alter spectroscopic features, and therefore, diagnostic absorption bands in the respective VCD spectra, and the sign and shape of the measured ECD curves could be used to determine and track the absolute stereochemistry of analogs without necessarily requiring time-consuming ab initio calculations of all low energy conformers for all compounds. VCD, OR, and ECD calculations for the determination of absolute configuration carried out at the DFT level with the hybrid B3PW91 functional and the TZVP basis set were found to be especially useful in this study.     

Chromatographic profiles of tryptophan and kynurenine enantiomers derivatized with (S)‐4‐(3‐isothiocyanatopyrrolidin‐1‐yl)‐7‐(N,N‐dimethylaminosulfonyl)‐2,1,3‐benzoxadiazole using LC–MS/MS on a triazole‐bonded column

d ‐ and l ‐Tryptophan (Trp) and d ‐ and l ‐kynurenine (KYN) were derivatized with a chiral reagent, (S )‐4‐(3‐isothiocyanatopyrrolidin‐1‐yl)‐7‐(N,N‐dimethylaminosulfonyl)‐2,1,3‐benzoxadiazole (DBD‐PyNCS), and were separated enantiomerically by high‐performance liquid chromatography (HPLC) equipped with a triazole‐bonded column (Cosmosil HILIC) using tandem mass spectrometric (MS/MS) detection. Effects of column temperature, salt (HCO₂NH₄) concentration, and pH of the mobile phase in the enantiomeric separation, followed by MS detection of (S )‐DBD‐PyNCS‐d ,l ‐Trp and ‐d ,l ‐KYN, were investigated. The mobile phase consisting of CH₃CN/10 mM ammonium formate in H₂O (pH 5.0) (90/10) with a column temperature of 50–60 °C gave satisfactory resolution (R s) and mass‐spectrometric detection. The enantiomeric separation of d ,l ‐Trp and d ,l ‐KYN produced R s values of 2.22 and 2.13, and separation factors (α) of 1.08 and 1.08, for the Trp and KYN enantiomers, respectively. The proposed LC–MS/MS method provided excellent detection sensitivity of both enantiomers of Trp and KYN (5.1–19 nM).     

Enantioselective ene‐reduction of E‐2‐cyano‐3‐(furan‐2‐yl) acrylamide by marine and terrestrial fungi and absolute configuration of (R)‐2‐cyano‐3‐(furan‐2‐yl) propanamide determined by calculations of electronic circular dichroism (ECD) spectra

This work reports the green organic chemistry synthesis of E‐2‐cyano‐3(furan‐2‐yl) acrylamide under microwave radiation (55 W), as well as the use of filamentous marine and terrestrial‐derived fungi, in the first ene‐reduction of 2‐cyano‐3‐(furan‐2‐yl) acrylamide to (R)‐2‐cyano‐3‐(furan‐2‐yl)propanamide. The fungal strains screened included Penicillium citrinum CBMAI 1186, Trichoderma sp. CBMAI 932 and Aspergillus sydowii CBMAI 935, and the filamentous terrestrial fungi Aspergillus sp. FPZSP 146 and Aspergillus sp. FPZSP 152. A compound with an uncommon CN‐bearing stereogenic center at the α‐C position was obtained by enantioselective reactions mediated in the presence of the microorganisms yielding the (R)‐2‐cyano‐3‐(furan‐2‐yl) propanamide 3a . Its isolated yield and e.e. ranged from 86% to 98% and 39% to 99%, respectively. The absolute configuration of the biotransformation products was determined by time‐dependent density functional theory (TD‐DFT) calculations of electronic circular dichroism (ECD) spectra. Finally, the tautomerization of 2‐cyano‐3‐(furan‐2‐yl) propanamide 3a to form an achiral ketenimine was observed and investigated in presence of protic solvents.     

Phloroglucinol Derivatives from Myrtus communis ‘Variegata’ and Their Antibacterial Activities

Myrtucomvalones D–F, three new triketone‐phloroglucinol‐triketone adducts, and three known ones (myrtucommulone E, myrtucommulone D and callistenone D) were obtained from Myrtus communis ‘Variegata’. Myrtucomvalone D is a pair of enantiomers which was further resolved into (+)‐myrtucomvalone D and (?)‐myrtucomvalone D by chiral HPLC. Their structures and complete stereochemistry were established from interpretation of NMR and crystallographic data and chemical calculations. Myrtucomvalone F, myrtucommulone D and callistenone D showed significant antibacterial activities.     

Syntheses and β‐adrenergic binding affinities of (R)‐ and (S)‐fluoronaphthyloxypropanolamines

The β‐adrenergic receptors mediate several physiological processes including heart rate (β₁), bronchodilation (β₂), and lipolysis (β₃). Therefore, selectivity is important for a possible therapeutic agent acting via these receptors. Aryloxypropanolamines are β‐receptor agonists or antagonists, depending on the aryl group and its substituents. We therefore hypothesized that fluorine substitution on the aromatic ring in this class could lead to significant biological effects because of the unique chemical characteristics of fluorine. Because the target compound has a chiral center, we set out to synthesize the two enantiomers so that effects of stereochemistry on biological activity could be evaluated. Syntheses of the enantiomers were performed starting with commercially available fluoronaphthalene and subsequent use of the chiral synthon (2R)‐ or (2S)‐glycidyl 3‐nitrobenzenesulfonate, depending on the desired enantiomer. High‐pressure liquid chromatography (HPLC) methods were used to characterize %ee. Each enantiomer was synthesized. They exhibited nanomolar binding activities on β‐adrenergic receptors. The (S)‐enantiomer was found to be up to 310 times more potent than the (R). It was also found to be about five‐fold more selective for β₂‐ than for β₁‐receptors. The current report demonstrates the importance of stereochemistry for the fluoroaromatic β‐receptor ligands. Chirality 11:144–148, 1999. © 1999 Wiley‐Liss, Inc.     

Determination of the Enantiomerization Barrier of the Residual Enantiomers of C3‐Symmetric Tris[3‐(1‐Methyl‐2‐Alkyl)Indolyl]Phosphane Oxides: Case Study of a Multitasking HPLC Investigation Based on an Immobilized Polysaccharide Stationary Phase

The residual enantiomers of three tris‐(3‐indolyl)‐phosphane oxides bearing different alkyl groups (methyl, ethyl or i‐propyl) in position 2 of the indole rings constituting the blades were separated on the immobilized type Chiralpak IC column in polar organic and reversed‐phase modes. The good enantioselectivity and versatility of the IC CSP allowed easy isolation of the enantiomerically highly enriched samples suitable for configurational stability studies. The enantiomerization barriers of residual phosphane oxides were evaluated both by off‐column techniques (CD signal and enantiomeric purity decay kinetics) and by dynamic enantioselective high‐performance liquid chromatography (HPLC). Chirality 27:888–899, 2015. © 2015 Wiley Periodicals, Inc.