- Synthesis and Stereochemical Revision of the C31–C67 Fragment of Amphidinol 3
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Amphidinol 3 (AM3) is a marine natural product produced by the dinoflagellate Amphidinium klebsii. Although the absolute configuration of AM3 was determined in 1999 by extensive NMR analysis and degradation of the natural product, it was a daunting task because of the presence of numerous stereogenic centers on the acyclic carbon chain and the limited availability from natural sources. Thereafter, revisions of the absolute configurations at C2 and C51 were reported in 2008 and 2013, respectively. Reported herein is the revised absolute configuration of AM3: 32S, 33R, 34S, 35S, 36S, and 38S based on the chemical synthesis of partial structures corresponding to the C31–C67 fragment of AM3 in combination with degradation of the natural product. The revised structure is unique in that both antipodal tetrahydropyran counterparts exist on a single carbon chain. The structural revision of AM3 may affect proposed structures of congeners related to the amphidinols.
- Wakamiya, Yuma,Ebine, Makoto,Murayama, Mariko,Omizu, Hiroyuki,Matsumori, Nobuaki,Murata, Michio,Oishi, Tohru
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- A Stimuli-Responsive Macromolecular Gear: Interlocking Dynamic Helical Polymers with Foldamers
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Herein, macromolecular gears composed of helical poly(phenylacetylenes) (PPAs) bearing short oligopeptides as pendant groups are described, in which the two structural motifs (framework and substituents) are combined. These gears are obtained by polymerization of the acetylene groups introduced at the C-terminus of short oligopeptides formed by achiral (Aib)n units (n=1–3) derivatized at the N-terminus by a single enantiomer (R or S) of α-methoxy-α-trifluoromethylphenylacetic acid (MTPA, Mosher's reagent). The chiral information of the MTPA is transmitted to the achiral Aib fragments and, through either chiral tele-induction and/or chiral harvesting mechanisms, is further transferred to the polyene backbones, which adopt preferentially P or M helical senses. Moreover, these materials also show dynamic behavior and respond to the action of external stimuli by either inverting the P/M sense and/or modifying the elongation in fully reversible processes.
- Freire, Félix,Qui?oá, Emilio,Riguera, Ricardo,Rodríguez, Rafael,Suárez-Picado, Esteban
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- Structure and natural occurrence of stereoisomers of the fumonisin B series mycotoxins
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1H and 13C NMR spectroscopy of both fumonisin B 3 and B4, as well as high-performance liquid chromatography (HPLC) analysis of samples of fumonisin B3 used as standards, showed in each case the presence of two stereoisomers, which could not be separated by preparative chromatography. The 2,3-anti relative configuration for the two minor stereoisomers of fumonisin B3 and B4 was deduced from the NMR data, and their 2S,3R absolute configurations were established by application of Mosher's method using the fumonisin B3 sample. Samples of fumonisin B3 and B 4 can contain between 10 and 40% of fumonisin B compounds of the 3-epi series. The 3-epi-FB3, determined by HPLC with fluorescence detection of the o-phthaldialdehyde derivative and confirmed by liquid chromatography-tandem mass spectrometry, was found to occur naturally in a range of maize samples at levels much lower than FB3 (20%). The identification of members of the 3-epi-fumonisin B series provides insight into the order and selectivity of steps in fumonisin biosynthesis.
- Gelderblom, Wentzel C. A.,Sewram, Vikash,Shephard, Gordon S.,Snijman, Petra W.,Tenza, Kenny,Van Der Westhuizen, Liana,Vleggaar, Robert
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- Stereoselective addition of Grignard reagents to (2-methyl-5-tert-butyl)phenyl 1-thio-β-D-ribopentodialdo-1,4-furanoside derivative
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Addition of a wide range of Grignard reagents to acetone protected (2-methyl-5-tert-butyl)phenyl 1-thio-β-D-ribopentodialdo-1,4-furanoside 3b produced useful 5(R)[sbnd]C-substituted products with moderate to good yields, and moderate to perfect stereoselectivities, with no need of additives. n.O.e. Analysis of 3b showed that 1-S-aryl group could contribute to the stereoselectivity of addition reaction. The stereochemistry of 4 representative 5-C-substituted ribofuranoside products was further confirmed by NMR study of corresponding Mosher esters, by chemical derivatization, or by single crystal study.
- Ren, Huanming,Xie, Wuchen,Xiong, Bing,Shen, Jingkang,Chen, Guohua,Chen, Yue-Lei
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- Synthesis and duplex-stabilizing properties of fluorinated N-methanocarbathymidine analogues locked in the C3'-endo conformation
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The efficient synthesis, antiviral activity, and duplex-stabilizing properties of both isomers of the 2'-fluoro analogue of Northern methanocarbathymidine (N-MCT), 2 and 3, are reported. We show that 2'-F incorporation on the N-MCT scaffold has a strong stabilizing effect on duplex thermal stability.
- Jung, Michael E.,Dwight, Timothy A.,Vigant, Frederic,stergaard, Michael E.,Swayze, Eric E.,Seth, Punit P.
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- NADH Mimics on Diacetone-D-glucose: Stereoselective Biomimetic Reduction of Benzoylformate and Interpretation of Chirality Transfer Deduced by Molecular Orbital Approach
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We have prepared novel NADH mimics, in which the 1,4-dihydronicotinamide structure is connected to the diacetone-D-glucose molecule via its C-1 nitrogen, e.g. compound 1a, and 1b, and through the amide bond, e.g. compound 2-6, and analyzed their ability to stereoselective reduction of methyl benzoylformate.Although NADH mimics 1-3 and 6 turned out to be less effective in chirality transfer toward methyl benzoylformate, much higher chirality transfer was observed in the reactions with the compounds (4 and 5) possesing free hydroxyl groups at 5',6'-position of furanose.Importance of an additional intramolecular coordinating substitutent to bivalent metal ion has been demonstrated in enhancing the stereoselectivity in the reduction of benzoylformate with such NADH mimics.To materialize these observation, transition-states of the hydride transfer from 1-methyl-1,4-dihydronicotinamide to methyl benzoylformate in the presence of magnesium (II) ion were calculated by semi-empirical molecular orbital method, MNDO-PM3.Also discussed in this paper is a general chirality transfer mechanism deduced from the theoretical transition-state modeling.
- Toyooka Yumiko,Matsuzawa, Toshihiro,Eguchi, Tadashi,Kakinuma, Katsumi
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- Hispidospermidin, a novel phospholipase C inhibitor produced by Chaetosphaeronema hispidulum (Cda) Moesz NR 7127: II - Isolation, characterization and structural elucidation
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Hispidospermidin (1) is a novel phospholipase C inhibitor produced by Chaetosphaeronema hispidulum (Cda) Moesz NR 7127. Its structure (C25H47N3O) has been elucidated as a cage compound with a trimethylspermidine side chain based on various NMR studies, including 1H-1H COSY, 13C-1H COSY, HOHAHA, HMBC, COLOC and long range J C-H resolved 2D spectroscopy. The absolute configuration of 1 has been elucidated by modified MOSHER's method on the (R)- and (S)-MTPA amides of a derivative of 1.
- Ohtsuka,Itezono,Nakayama,Sakai,Shimma,Yokose,Seto
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- Antiprotozoal activities of heterocyclic-substituted xanthones from the marine-derived fungus Chaetomium sp.
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Investigations of the marine-derived fungus Chaetomium sp. led to the isolation of the new natural products chaetoxanthones A, B, and C (1-3). Compounds 1 and 2 are substituted with a dioxane/tetrahydropyran moiety rarely found in natural products. Compound 3 was identified as a chlorinated xanthone substituted with a tetrahydropyran ring. The configurational analysis of these compounds employed CD spectroscopy, modified Mosher's method, and selective NOE gradient measurements. Compound 2 showed selective activity against Plasmodium falciparum with an IC50 value of 0.5 μg/mL without being cytotoxic toward cultured eukaryotic cells. Compound 3 displayed a moderate activity against Trypanosoma cruzi with an IC50 value of 1.5 μg/mL.
- Pontius, Alexander,Krick, Anja,Kehraus, Stefan,Brun, Reto,Koenig, Gabriele M.
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- On the specificity of reactions catalysed by the antibody H11
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The substrate specificity and the stereochemical course of the reactions catalysed by the antibody H11 (which was raised to a protein conjugated derivative of the adduct of 1-acetoxy-buta-1,3-diene 1) have been investigated. The antibody shows high selectivity for acetoxybutadiene which it hydrolyses to the corresponding dienol, the major diene component of the cycloaddition reactions observed. However, it tolerates a range of N- alkylmaleimides. The stereochemical course of cycloaddition is shown to produce a significant enantiomeric excess of the 3aR, 4S, 7aR-endo- diastereoisomer by analysis with Mosher's ester derivatives. This study also revealed that H11 is capable of slowly catalysing the hydrolysis of N- alkylmaleimide substrates. The implications for the mechanism of action of H11 are discussed. (C) 2000 Elsevier Science Ltd.
- Khalaf, Abedawn I.,Linaza, Sabin,Pitt, Andrew R.,Stimson, William H.,Suckling, Colin J.
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- Novel synthesis of purine acyclonucleosides possessing a chiral 9-hydroxyalkyl group by sugar modification of 9-D-ribitylpurines
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A novel approach to the synthesis of purine acyclonucleosides having chiral carbons in the N9-hydroxyalkyl chain was achieved by using 9-(2,3-O-isopropylidene-D-ribityl)purines 1, which are readily prepared from commercially available purine nucleosides. 9-[(2S,3.R)-2,3,4-Trihydroxybutyl]purines 4a and 4b, 9-[(2S,3S)-2,3,4-trihydroxybutyl]purines 6a and 6b, L-eritadenine 8, and its analogue 11 are conveniently synthesized via key intermediates, (2S,3S)-2,3-isopropylidenedioxy-4-(purin-9-yl)butanals 2 prepared by NaIO4 oxidation of diols 1.
- Hirota, Kosaku,Monguchi, Yasunari,Sajiki, Hironao,Sako, Magoichi,Kitade, Yukio
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- Pinguisane and dimeric pinguisane-type sesquiterpenoids from the Japanese liverwort Porella acutifolia subsp. tosana
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Two new pinguisane-type, three new Diels-Alder reaction-type dimeric pinguisane sesquiterpenoids and known sesqui and diterpenoids were isolated from the ether extract of the Japanese liverwort Porella acutifolia subsp. tosana. Their absolute stereostructures were established by a combination of extensive 2D-NMR, CD spectra, X-ray crystallographic analysis, modified Mosher's method and chemical correlation. (C) 2000 Elsevier Science Ltd.
- Hashimoto, Toshihiro,Irita, Hiroshi,Tanaka, Masami,Takaoka, Shigeru,Asakawa, Yoshinori
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- Chemical Synthesis of the (1R,2S) and (1S,2R) Arene Oxide Metabolites of Acridine
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Enantiopure samples of (+)-(1R,2S) and (-)-(1S,2R)-1,2-epoxy-1,2-dihydroacridine 4 have been obtained from the corresponding trans-2-bromo-1,2,3,4-tetrahydroacridin-1-ol MTPA esters 7a and b.Absolute configurations were deduced by stereochemical correlation to (+)-(1R,2R)-trans-2-bromo-1-(2-methoxy-2-phenyl-2-trifluoroacetoxy)-1,2,3,4-acridine 7a which was unequivocally assigned by X-ray crystal structure analysis. (-)-(1R,2R)-trans-1,2-Dihydroacridine-1,2-diol 2 was obtained by alkaline hydrolysis of (+)-(1R,2S)-acridine 1,2-oxide 4.
- Boyd, Derek R.,Dorrity, Michael R. J.,Hamilton, Lynne,Malone, John F.,Smith, Allison
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- Enzymatic resolution of the 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane (1,8-cineole) system
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Regioselective oxidation of 1,8-cineole 1 with chromyl acetate according to a literature procedure gave the bicyclic 2-ketocineole 8 as the major product along with the symmetrical diketocineole 9. The bicyclic monoketone was reduced with lithium aluminum hydride followed by exposure to acetyl chloride/DMAP to afford the exo-acetate (±)-4b. Pig liver esterase (PLE)-mediated hydrolysis of the racemic acetate provided the alcohol (-)-2b (45%) together with its antipodal acetate (+)-4b (43%) in greater than 99% enantiomeric purity, as determined by analysis of the Mosher's ester derivatives. Iodination of the alcohol exo-(+)-2b, obtained by hydrolysis of the resolved actetate with iodine/triphenylphosphine/imidazole, provided the corresponding endo iodide (-)-12a, which was easily dehydrohalogenated with DBU under solvent-free conditions to provide the corresponding cineolene (-)-6 in an overall yield of 6 and 99% e.e.
- Luzzio, Frederick A.,Duveau, Damien Y.
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- Diterpenoids and Bisnorditerpenoids from Blumea aromatica
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Three new labdane-type diterpenoids, 6α-O-isovalerylnidorellol (1), (12S)-blumdane (2), and (12R)-epiblumdane (3), and three new bisnorditerpenoids, 6α-O-(3-methyl-2-butenoyl)sterebin A (5), 6α-O-angeloylsterebin A (6), and 6α-O-isovalerylsterebin A (7), plus 17 known compounds were isolated from Blumea aromatica. Their structures of the new compounds were proposed by detailed spectroscopic analysis. The absolute configuration at C-12 of blumdane (2) was determined by the modified Mosher's method. The anti-inflammatory and anti-immunosuppressive effects of these isolated compounds were assessed. Compounds 9, 16, and 23 (at 40 μM) showed a slight suppression of TNF-α production, but no or little effect on the expression of PD-L1 in granulocytic myeloid-derived suppressor cells was observed for all test compounds.
- Shen, Chien-Chang,Wei, Wen-Chi,Lin, Lie-Chwen
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- Photochemical Electrocyclization of Poly(phenylacetylene)s: Unwinding Helices to Elucidate their 3D Structure in Solution
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Photochemical electrocyclization of poly(phenylacetylene)s (PPAs) is used for the structural elucidation of a polyene backbone. This method not only allows classification of PPAs in cis-cisoidal (ω11>90°), but also approximating ω1. A PPA solution is illuminated with visible light and monitoring the photochemical electrocyclization of the PPA helix by measuring the ECD spectra at different times. PPAs with a cis-cisoidal structure show a reduction of the ECD signal of at least 50 % before 30 min of irradiation, while cis-transoidal helices need much longer time because the transoidal bond must be isomerized. The different cis-cisoidal and cis-transoidal helices require different times to decrease their ECD signal by 50 % (t1/2), depending on the degree of compression or stretching of the helix, establishing a relationship between the secondary structure adopted by PPA (ω1) and the time required to lose the ECD vinylic signal by light irradiation.
- Rey-Tarrío, Francisco,Rodríguez, Rafael,Qui?oá, Emilio,Riguera, Ricardo,Freire, Félix
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- Computer-aided design of chiral ligands. Part III. A novel ligand for asymmetric allylation designed using computational techniques.
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[reaction: see text] Computer-aided design protocols to identify new chiral ligands for reactions proceeding through well-defined transition states are outlined. Ligand families are discovered via computational screening of large structural databases such as the Cambridge Structural Database. Using this method, a novel cis-decalin ligand has been identified as a chiral auxiliary for the allylboration of aldehydes. Synthesis, resolution, and evaluation revealed that this new auxiliary provided the aldehyde facial approach upon which the design was predicated.
- Kozlowski, Marisa C,Waters, Stephen P,Skudlarek, Jason W,Evans, Catherine A
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- Total Syntheses of (+)- and (-)-Tetrapetalones A and C
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Described herein are syntheses of the naturally occurring polyketides (-)-tetrapetalones A and C and their respective enantiomers. The employed strategy involves initial assembly of a masked N-aryl tetramic acid which is advanced via a highly selective conjugate addition/intramolecular Friedel-Crafts acylation sequence to deliver a key azepine intermediate. Application of recently developed C-H activation chemistry and subsequent Heck cyclization delivers the aglycone framework in an overall 12 steps. Resolution of the aglycone via stereospecific glycosylation with an enantiopure glycosyl donor followed by separation of the derived diastereomers enables further advancement to either (+)- or (-)-tetrapetalones A and C.
- Dhanjee, Heemal H.,Kobayashi, Yutaka,Buergler, Jonas F.,McMahon, Travis C.,Haley, Matthew W.,Howell, Jennifer M.,Fujiwara, Koichi,Wood, John L.
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- STEREOCHEMISTRY OF THE SPIROBIFLAVONOID GENKWANOL B FROM DAPHNE GENKWA
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The absolute configuration of genkwanol B isolated from Daphne genkwa was studied and assigned as C-2(R), C-3(S), C-8(S), C-2"(S) and C-3"(R) by modified Mosher's method and the X-ray analysis of a pentamethyl ether acetate.Key Word Index - Daphne genkwa; Thymelaeaceae; spirobiflavonoid; genkwanol B; stereochemistry; X-ray analysis; modified Mosher's method.
- Baba, Kimiye,Taniguchi, Masahiko,Ohishi, Hirofumi,Kozawa, Mitsugi
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- Cross-metathesis approach for stereocontrolled synthesis of the C1-C15 fragment of rhizopodin
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The C1-C15 fragment of rhizopodin was synthesized through either Suzuki coupling reaction of vinyl iodide and vinyl boronate or cross-metathesis of a terminal olefin and a diene adduct in the presence of Hoveyda-Grubbs II catalyst. Georg Thieme Verlag Stuttgart · New York.
- Gui, Honggang,Liu, Junyang,Song, Liankai,Hui, Chunngai,Feng, Junmin,Xu, Zhengshuang,Ye, Tao
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- Absolute configuration of myrobotinol, new fused-hexacyclic alkaloid skeleton from Myrioneuron nutans
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(Chemical Equation Presented) Myrobotinol (1) was isolated from the leaves of Myrioneuron nutans (Rubiaceae) and its structure determined from spectral data, including mass spectrometry and 2D NMR. This compound presents a new hexacyclic alkaloid skeleton including a 1,3-oxazine and aminal functionality. The absolute configuration of myrobotinol was established by using Mosher's method. A plausible biosynthetic pathway starting from L-lysine via Δ-piperideine was proposed for this hexacyclic alkaloid.
- Van, Cuong Pham,Jossang, Akino,Sevenet, Thierry,Van, Hung Nguyen,Bodo, Bernard
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- Studies toward the Synthesis of Iriomoteolide-2a: Construction of the C(6)-C(28) Fragment
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The synthesis of an appropriately functionalized advanced C(6-28) fragment (3) of the marine macrolide iriomoteolide-2a (1) has been achieved in a highly efficient manner. The C(6)-C(18) fragment of 1 is prepared via a radical cyclization of a vinyl ether intermediate and palladium-promoted hydrostannylation/iodination. Paterson aldol reaction and Peterson olefination are used to construct the C(19)-C(28) fragment. The union of the C(6)-C(18) and C(19)-C(28) fragments is accomplished via a Suzuki-Miyaura coupling reaction.
- Wang, Lushun,Wu, Fusong,Jia, Xuelei,Xu, Zhengshuang,Guo, Yian,Ye, Tao
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- Synthesis, Absolute Configurations, and Biological Activities of Floral Scent Compounds from Night-Blooming Araceae
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The uncommon jasmone derivatives dehydrojasmone, isojasmol, and isojasmyl acetate, floral scent compounds from night-blooming Araceae, were synthesized in a scalable synthesis employing conjugate addition with a selenoacetal as the key step. The stereoselective strategy with subsequent enzymatic kinetic resolution allowed determining the absolute configuration of the natural compounds by GC on a chiral phase. The homoterpene (E)-4,8-dimethyl-1,3,7-nonatrien-5-yl acetate, another uncommon scent compound, was obtained by α-regioselective aldehyde prenylation. The biological activities of dehydrojasmone and isojasmol were investigated in field assays, showing that these unique volatiles are able to selectively attract specific cyclocephaline scarab beetle pollinators.
- Stamm, Patrick,Etl, Florian,Maia, Artur Campos D.,D?tterl, Stefan,Schulz, Stefan
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p. 5245 - 5254
(2021/04/12)
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- Multigram Preparation of BRD4780 Enantiomers and Assignment of Absolute Stereochemistry
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The development of a multigram synthesis of 3-exo-isopropylbicyclo[2.2.1]heptan-2-endo-amine hydrochloride (1) (also known as BRD4780 and AGN-192403) is described. The process involves protection of the amine as 4-nitrobenzyl carbamate, pNZ, which enables chiral SFC chromatography. The absolute configuration (AC) of the individual enantiomers has been determined by Mosher's amide method, VCD spectroscopy, and X-ray crystallography. We highlight the VCD approach as a rapid and effective means of AC determination that can be deployed directly on the target compounds.
- Chamberlain, Brian T.,Vincent, Mathilde,Nafie, Jordan,Müller, Peter,Greka, Anna,Wagner, Florence F.
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p. 4281 - 4289
(2021/03/09)
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- Studies toward norzoanthamine: Ireland–Claisen rearrangements of α,β-unsaturated esters in a stereocontrolled synthesis of trans-fused 2-cyclohexen-1-ones
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The enantiocontrolled preparation of the trans-fused ABC ring system of norzoanthamine is described. The synthesis strategy has incorporated studies of Ireland–Claisen rearrangements of esters derived from 3,3-dimethylacrylic acid. Stereocontrol results from competing chair- and boat-like transition states. Introduction of a nitroalkene by application of a modified Henry reaction facilitates an intramolecular Diels–Alder cycloaddition for an effective and simple transformation to the desired conjugated decalone. A fully functionalized AB ring system leads to the cyclization of the trans-fused cyclohexenone to complete the ABC system via ring-closing metathesis.
- Gladen, Paul T.,Patnaik, Samarjit,Williams, David R.
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- Chiral 2-phenyl-3-hydroxypropyl esters as PKC-alpha modulators: HPLC enantioseparation, NMR absolute configuration assignment, and molecular docking studies
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Protein kinase C (PKC) isoforms play a pivotal role in the regulation of numerous cellular functions, making them extensively studied and highly attractive drug targets. In our previous work, we identified in racemate 1–2, based on the 2-benzyl-3-hydroxypropyl ester scaffold, two new potent and promising PKCα and PKCδ ligands, targeting the C1 domain of these two kinases. Herein, we report the resolution of the racemates by enantioselective semi-preparative HPLC. The attribution of the absolute configuration (AC) of homochirals 1 was performed by NMR, via methoxy-α-trifluoromethyl-α-phenylacetic acid derivatization (MTPA or Mosher's acid). Moreover, the match between the experimental and predicted electronic circular dichroism (ECD) spectra confirmed the assigned AC. These results proved that Mosher's esters can be properly exploited for the determination of the AC also for chiral primary alcohols. Lastly, homochiral 1 and 2 were assessed for binding affinity and functional activity against PKCα. No significative differences in the Ki of the enantiopure compounds was observed, thus suggesting that chirality does not seem to play a significant role in targeting PKC C1 domain. These results are in accordance with the molecular docking studies performed using a new homology model for the human PKCαC1B domain.
- Amadio, Marialaura,Ann, Jihyae,Blumberg, Peter M.,Collina, Simona,Lee, Jeewoo,Linciano, Pasquale,Listro, Roberta,Minneci, Marco,Mitchell, Gary A.,Nasti, Rita,Pascale, Alessia,Potenza, Donatella,Rossi, Daniela,Vasile, Francesca,Zhou, Xiaoling
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- N-Ammonium Ylide Mediators for Electrochemical C-H Oxidation
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The site-specific oxidation of strong C(sp3)-H bonds is of uncontested utility in organic synthesis. From simplifying access to metabolites and late-stage diversification of lead compounds to truncating retrosynthetic plans, there is a growing need for new reagents and methods for achieving such a transformation in both academic and industrial circles. One main drawback of current chemical reagents is the lack of diversity with regard to structure and reactivity that prevents a combinatorial approach for rapid screening to be employed. In that regard, directed evolution still holds the greatest promise for achieving complex C-H oxidations in a variety of complex settings. Herein we present a rationally designed platform that provides a step toward this challenge using N-ammonium ylides as electrochemically driven oxidants for site-specific, chemoselective C(sp3)-H oxidation. By taking a first-principles approach guided by computation, these new mediators were identified and rapidly expanded into a library using ubiquitous building blocks and trivial synthesis techniques. The ylide-based approach to C-H oxidation exhibits tunable selectivity that is often exclusive to this class of oxidants and can be applied to real-world problems in the agricultural and pharmaceutical sectors.
- Saito, Masato,Kawamata, Yu,Meanwell, Michael,Navratil, Rafael,Chiodi, Debora,Carlson, Ethan,Hu, Pengfei,Chen, Longrui,Udyavara, Sagar,Kingston, Cian,Tanwar, Mayank,Tyagi, Sameer,McKillican, Bruce P.,Gichinga, Moses G.,Schmidt, Michael A.,Eastgate, Martin D.,Lamberto, Massimiliano,He, Chi,Tang, Tianhua,Malapit, Christian A.,Sigman, Matthew S.,Minteer, Shelley D.,Neurock, Matthew,Baran, Phil S.
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supporting information
p. 7859 - 7867
(2021/05/26)
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- Synthetic Studies toward Tubiferal A: Asymmetric Synthesis of a Model ABC-Ring Compound
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Synthetic studies on an ABC-ring model of tubiferal A, a triterpenoid isolated from the fruit bodies of the Tubifera dimorphotheca myxomycete, are described. The stereogenic centers at the angular positions were constructed through the stereoselective addition of a Cring allylborane followed by an Eschenmoser-Claisen rearrangement reaction prior to the formation of the AB-ring system by a double intramolecular alkylation reaction of a dichloro nitrile intermediate.
- Hiramatsu, Takahiro,Ikeuchi, Kazutada,Itoh, Ryusei,Suzuki, Takahiro,Tanino, Keiji,Yukutake, Yuki
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- Constituents of Bupleurum praealtum and Bupleurum veronense with Potential Immunomodulatory Activity
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In this investigation, chromatographic separations of the diethyl ether extracts of two European annual Bupleurum taxa, B. praealtum and B. veronense, yielded nine new natural products, namely, a series of esters of stereoisomeric tetradeca-5,7,9,11-tetraen-1-ols (1-4 and 8), a tetra-unsaturated γ-tetradecalactone (5), a dibenzylbutyrolactone lignan (7-oxoarcitin, 6), a falcarinol-related 17-membered macrolide (7) possessing a conjugated diyne-system, and an acylphloroglucinol derivative (9). All these new compounds were fully characterized by NMR, IR, UV, MS, and optical rotation measurement, including 1H NMR full spin spectral simulation, whereas the absolute configurations of 1, 5, and 9 were determined via chemical correlations and NMR analysis of Mosher esters. The in vitro potential immunomodulatory activities of 1, 4, 5, and (+)-arcitin were assessed by determining their effects on the functional properties of isolated rat splenocytes and peritoneal macrophages. The results obtained support the known immunomodulatory ethnomedicinal usage of Bupleurum species.
- Ne?i?, Milan,Radulovi?, Niko,Ran?elovi?, Pavle,Ran?elovi?, Vladimir,Stevanovi?, Milica,Stojanovi?, Nikola
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p. 2902 - 2914
(2020/11/03)
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- Controlled Reduction of Carboxamides to Alcohols or Amines by Zinc Hydrides
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New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX2). Use of a different halide on ZnX2 dictates the selectivity, wherein the NaH-ZnI2 system delivers alcohols and NaH-ZnCl2 gives amines. Extensive mechanistic studies by experimental and theoretical approaches imply that polymeric zinc hydride (ZnH2)∞ is responsible for alcohol formation, whereas dimeric zinc chloride hydride (H?Zn?Cl)2 is the key species for the production of amines.
- Ong, Derek Yiren,Yen, Zhihao,Yoshii, Asami,Revillo Imbernon, Julia,Takita, Ryo,Chiba, Shunsuke
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supporting information
p. 4992 - 4997
(2019/03/13)
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- Asymmetric synthesis of (S)-dihydrokavain from l-malic acid
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A practical and efficient asymmetric synthesis of (S)-dihydrokavain from known ethyl (S)-2-hydroxy-4-phenylbutanoate which is, in turn, readily available from l-malic acid as a cheap chiral pool material is described using regioselective ring-opening of the 1,2-cyclic sulfate with lithium-3,3,3-triethoxypropiolate and subsequent HgO/H2SO4-mediated lactonization as the key steps. Its opposite enantiomer (R)-dihydrokavain was also synthesized from d-malic acid using the same sequences of reactions for the purpose of optical purity determination.
- Eskici, Mustafa,Karanfil, Abdullah,?zer, M. Sabih,Kabak, Yal??n,Durucasu, ?nci
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supporting information
p. 2382 - 2390
(2018/10/20)
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- Enantioselective Synthesis of (+)-Mitomycin K by a Palladium-Catalyzed Oxidative Tandem Cyclization
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The mitomycins, a family of bioactive natural products, feature a compact 6/5/5-fused polycyclic ring structure densely decorated with highly reactive and/or fragile quinone, amino ketal, and aziridine as well as carbamate moieties. It is this striking feature that has defeated numerous synthetic attempts towards these apparently small molecules, rendering them one of the most formidable targets for total synthesis. We herein report the first enantioselective synthesis of (+)-mitomycin K, a representative of G series mitomycins. The key step of this synthesis is an enantioselective oxidative cyclization catalyzed by a palladium/(+)-sparteine system that had previously been developed by our group. The robustness of this method bodes well for further applications in the asymmetric total synthesis of natural products, particularly those with characteristic 6/5/5-fused pyrroloindole skeletons.
- Gu, Qiang-Shuai,Yang, Dan
-
supporting information
p. 5886 - 5889
(2017/05/12)
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- Chiral phosphoric acid catalyzed enantioselective annulation of acyclic enecarbamates to: In situ -generated ortho -quinone methides
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The first organocatalytic asymmetric reaction of acyclic enecarbamates with o-quinone methides is disclosed. BINOL-based phosphoric acid catalysts were found to be suitable for the annulation reaction. With 10 mol% of the TRIP catalyst, high yields as well as excellent diastereo- and enantioselectivities are achieved for a variety of 2,3,4-trisubstituted chroman products.
- Gharui, Chandan,Singh, Shreya,Pan, Subhas Chandra
-
supporting information
p. 7272 - 7276
(2017/09/25)
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- Highly stereoselective kinetic resolution of α-allenic alcohols: An enzymatic approach
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A highly efficient lipase AK-catalyzed direct kinetic resolution of a variety of α-allenic alcohols was developed. With the complementary to previous studies, the current reaction system is effective on a broad range of substituents (R1) at C(1), such as alkyl, aryl, alkenyl, and alkynyl groups. The Jones-Burgess empirical model was modified to interpret the reversed selectivity during the acetylation of secondary alcohol. The methyl group at C(2) of allenic alcohols implied a small structural adjustment in the catalytic triad of lipase AK, representing a potential direction for future site-directed mutagenesis.
- Li, Wenhua,Lin, Zuming,Chen, Long,Tian, Xuechao,Wang, Yan,Huang, Sha-Hua,Hong, Ran
-
supporting information
p. 603 - 606
(2016/01/20)
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- Enantioselective Rhodium-Catalyzed Atom-Economical Macrolactonization
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A highly attractive route toward macrolactones, which form the cyclic scaffold of a multitude of diverse natural compounds, is described. Although many chemical approaches to this structural motif have been explored, an asymmetric variant of the cyclization is unprecedented. Herein we present an enantioselective macrolactonization through an intramolecular atom-economical rhodium-catalyzed coupling of ω-allenyl-substituted carboxylic acids. The use of a modified diop ligand, chiral DTBM-diop, led to high enantioselectivity (up to 93 % ee). The reaction tolerated a large variety of functionalities, including α,β-unsaturated carboxylic acids and depsipeptides, and provided the desired macrocycles with very high enantio- and diastereoselectivity.
- Ganss, Stephanie,Breit, Bernhard
-
supporting information
p. 9738 - 9742
(2016/08/10)
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- Laboratory scale-up synthesis of chiral carbinols using Rhizopus arrhizus
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Rhizopus arrhizus mediated bioreduction was optimized using acetophenone as a model substrate. Various parameters such as bio-processing conditions, reaction time, substrate concentration, temperature, and solvent carrier were studied. This optimized protocol was further exploited for scaled up bioreductions of various prochiral ketones. This study demonstrates the versatility of the fungus Rhizopus arrhizus as a biocatalyst to obtain chiral carbinols in good to excellent yields and selectivities.
- Salvi, Neeta A.,Chattopadhyay, Subrata
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p. 188 - 192
(2018/10/09)
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- BICYCLIC CARBOCYCLIC NUCLEOSIDES AND OLIGOMERIC COMPOUNDS PREPARED THEREFROM
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The present invention provides novel bicyclic carbocyclic nucleosides and oligomeric compounds prepared therefrom. Incorporation of one or more of the bicyclic carbocyclic nucleosides into an oligomeric compound is expected to enhance one or more properties of the oligomeric compound. In certain embodiments, the oligomeric compounds provided herein hybridize to a portion of a target RNA resulting in modulation of normal function of the target RNA. In certain embodiments, bicyclic carbocyclic nucleosides are provided as monomers for use as antivirals.
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-
Page/Page column 89; 90
(2015/11/10)
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- Enantioselective cross-coupling of meso -epoxides with aryl halides
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The first enantioselective cross-electrophile coupling of aryl bromides with meso-epoxides to form trans-β-arylcycloalkanols is presented. The reaction is catalyzed by a combination of (bpy)NiCl2 and a chiral titanocene under reducing conditions. Yields range from 57 to 99% with 78-95% enantiomeric excess. The 30 examples include a variety of functional groups (ether, ester, ketone, nitrile, ketal, trifluoromethyl, sulfonamide, sulfonate ester), both aryl and vinyl halides, and five- to seven-membered rings. The intermediacy of a carbon radical is strongly suggested by the conversion of cyclooctene monoxide to an aryl [3.3.0]bicyclooctanol.
- Zhao, Yang,Weix, Daniel J.
-
supporting information
p. 3327 - 3340
(2015/03/30)
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- Enantioselective synthesis of allenylenol silyl ethers via chiral lithium amide mediated reduction of ynenoyl silanes and their Diels-Alder reactions
-
An enantioselective Meerwein-Ponndorf-Verley-type reduction of ynenoylsilanes by a chiral lithium amide followed by a Brook rearrangement and anti-mode protonation across conjugated 1,3-enynes provides allene derivatives bearing a 2-siloxyvinyl moiety in high enantioselectivity. The E/Z geometry of enol silyl ethers is controlled by the geometry of the starting enyne moiety. Thus, (E)- and (Z)-enol silyl ethers are obtained from (Z)- and (E)-ynenoylsilans, respectively. The 2-siloxyvinylallene products can participate in Diels-Alder reactions with reactive dienophiles such as PTAD, which can be achieved in a one-pot operation from ynenoylsilanes.
- Sasaki, Michiko,Kondo, Yasuhiro,Moto-Ishi, Ta-Ichi,Kawahata, Masatoshi,Yamaguchi, Kentaro,Takeda, Kei
-
supporting information
p. 1280 - 1283
(2015/03/14)
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- Anaerobic nitroxide-catalyzed oxidation of alcohols using the NO +/NO· redox pair
-
A new method for alcohol oxidation using TEMPO or AZADO in conjunction with BF3·OEt2 or LiBF4 as precatalysts and tert-butyl nitrite as a stoichiometric oxidant has been developed. The system is based on a NO+/NO· pair for nitroxide reoxidation under anaerobic conditions. This allows the simple, high-yielding conversion of various achiral and chiral alcohols to carbonyl compounds without epimerization and no formation of nonvolatile byproducts.
- Holan, Martin,Jahn, Ullrich
-
supporting information
p. 58 - 61
(2014/01/23)
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- Mosher's amide-based assignment of the absolute configuration of phantasmidine
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The absolute configuration of phantasmidine was assigned by analysis of the two conformers of the two Mosher amides. The expected shielding of the protons adjacent to the nitrogen and large long range shielding (～1 ppm) of the cyclobutane methylene protons in 16major and the pyridine protons of 16minor by the phenyl group of the Mosher amide allows the assignment of absolute configuration as shown in Schemes 4 and 5.
- Zhou, Quan,Snider, Barry B.
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p. 779 - 787
(2016/10/30)
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- Unexpected diels-Alder/carbonyl-ene cascade toward the biomimetic synthesis of chloropupukeananin
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The biomimetic synthesis of the advanced model compound of chloropupukeananin has been achieved. The present synthesis features an unexpected enantiomer-differentiating Diels-Alder/carbonyl-ene cascade under high-pressure conditions and a base-promoted migration of the salicyl group.
- Suzuki, Takahiro,Miyajima, Yuria,Suzuki, Kaname,Iwakiri, Kanako,Koshimizu, Masaki,Hirai, Go,Sodeoka, Mikiko,Kobayashi, Susumu
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supporting information
p. 1748 - 1751
(2013/07/05)
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- Explorations into the potential of chiral sulfonium reagents to effect asymmetric halonium additions to isolated alkenes
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While methods for the racemic dihalogenation and halohydroxylation of alkenes have been known for decades, enantioselective variants of these processes remain elusive. Initial attempts were made to overcome this long-standing challenge by exploring the potential of chiral, crystalline, sulfur-derived halonium reagents to accomplish the asymmetric dichlorination and iodohydroxylation of 1,2-dihydronaphthalene. Asymmetric dichlorination of this substrate was achieved in 57% yield and 14% enantiomeric excess (ee), but asymmetric iodohydroxylation was much more successful, giving 67% yield and 63% ee. Thorough studies were made of these processes, including investigation of various chiral sulfide derivatives, their substrate scopes, and the reaction conditions. Georg Thieme Verlag Stuttgart · New York.
- Brucks, Alexandria P.,Treitler, Daniel S.,Liu, Shu-An,Snyder, Scott A.
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p. 1886 - 1898
(2013/07/26)
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- Enantioselective synthesis of (-)-stemoamide
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An enantioselective synthesis of (-)-stemoamide is presented. Noyoris ruthenium complex catalyzed asymmetric transfer hydrogenation of an alkynone delivered the (S)-C8 stereogenic center in 97.7% ee. An iron(III) chloride promoted and bioinspired N-iminium ion cyclization afforded a 3:1 ratio of two diastereomers in favor of the cis-isomer. The diastereomeric ratio was enriched to 50:1 by a silver-catalyzed cycloisomerization. The subsequent dynamic ruthenium-catalyzed CO-insertion reaction secured an enantioselective total synthesis of (-)-stemoamide in 18% overall yield with high optical purity.
- Mi, Xianwei,Wang, Yan,Zhu, Lili,Hong, Ran,Wang, Renxiao
-
supporting information
p. 3432 - 3440,9
(2012/12/12)
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- Enantioselective synthesis of (-)-stemoamide
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An enantioselective synthesis of (-)-stemoamide is presented. Noyoris ruthenium complex catalyzed asymmetric transfer hydrogenation of an alkynone delivered the (S)-C8 stereogenic center in 97.7% ee. An iron(III) chloride promoted and bioinspired N-iminium ion cyclization afforded a 3:1 ratio of two diastereomers in favor of the cis-isomer. The diastereomeric ratio was enriched to 50:1 by a silver-catalyzed cycloisomerization. The subsequent dynamic ruthenium-catalyzed CO-insertion reaction secured an enantioselective total synthesis of (-)-stemoamide in 18% overall yield with high optical purity. Georg Thieme Verlag KG - Stuttgart - New York.
- Mi, Xianwei,Wang, Yan,Zhu, Lili,Wang, Renxiao,Hong, Ran
-
supporting information
p. 3432 - 3440
(2013/01/15)
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- Pd(II)/Bronsted acid catalyzed enantioselective allylic C-H activation for the synthesis of spirocyclic rings
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A Pd(II)/Bronsted acid catalyzed migratory ring expansion for the synthesis of indene derivatives possessing a stereogenic spirocyclic carbon center was developed. This transformation is believed to mechanistically proceed via enantioselective allylic C-H activation with concomitant semipinacol ring expansion to the nascent π-allylpalladium species. Enantioselectivities as high as 98% ee were attainable.
- Chai, Zhuo,Rainey, Trevor J.
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supporting information; experimental part
p. 3615 - 3618
(2012/04/23)
-
- Heteroatom-directed Wacker oxidations. A protection-free synthesis of (-)-heliophenanthrone
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The first enantioselective six-step synthesis of (-)-heliophenanthrone has been achieved without any protection-deprotection protocol at an overall yield of 28%. Key features of this synthesis comprise a heteroatom-directed Wacker oxidation of an internal cyclic olefin in addition to asymmetric Brown allylation and ring closing metathesis (RCM). The Royal Society of Chemistry 2012.
- Mukherjee, Parag,Sarkar, Tarun K.
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supporting information; experimental part
p. 3060 - 3065
(2012/05/07)
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- PREPARATION OF PHANTASMIDINE AND ANALOGUES THEREOF
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Described are methods of synthesizing phantasmidine and analogues thereof from commercially available starting materials. The compounds are useful as pharmacological probes and potential lead compounds for the development of selective nicotinic receptor therapeutics.
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-
Page/Page column 37-38
(2012/06/30)
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- 1,5-Stereocontrol in tin(IV) halide mediated reactions between N- and S-substituted pent-2-enylstannanes and aldehydes or imines
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Following transmetalation of (4S)-4-(dibenzylamino)pent-2-enyl(tributyl) stannane with tin(IV) bromide, reactions of the resulting allyltin tribromide with aldehydes gave (3Z)-1,5-syn-5-(dibenzylamino)hex-3-en-1-ols with excellent, ca. 98:2, stereocontrol. (4R)-5-Benzylthio-4-methylpent-2-enyl(tributyl) stannane similarly reacted with aldehydes to give (3Z)-1,5-anti-6-benzylthio-5- methylhex-3-en-1-ols with 87:13 stereocontrol. Although the analogous reaction of (4R)-4-benzylthiopent-2-enyl(tributyl)stannane with benzaldehyde proceeded with some stereoselectivity, 80-90:20-10, in favour of the (3Z)-1,5-syn- diastereoisomer, the yield was low due to a competing Lewis acid catalysed 1,4-elimination. N-Acylamino- and S-acylthio-pent-2-enylstannanes reacted with aldehydes with variable syn/anti-stereoselectivities. Tin(IV) chloride promoted reactions of the 4-(dibenzylamino)pent-2-enylstannane with 1- alkoxycarbonylimines gave (E)-alk-4-enoates with a modest preference for the 2,6-anti-products, 2,6-anti/2,6-syn=75:25.
- Stanway, Steven J.,Thomas, Eric J.
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experimental part
p. 5998 - 6009
(2012/09/08)
-
- A total synthesis of herboxidiene methyl ester
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The total synthesis of the methyl ester, 35, of herboxidiene (1, a.k.a. GEX1A and TAN-1609), a polyketide displaying both herbicidal and anti-tumor activity, is described. The convergent reaction sequence involves, in its closing stages, the union of the phosphine oxide 3 with the aldehyde 21 to deliver, via a Horner-Wittig reaction with accompanying epimerization at C12, compound 33 that after deprotection affords an alcohol, 34, capable of participating in a regioand diastereo-selective epoxidation reaction to give target 35. Phosphine oxide 3 was prepared via the intramolecular hetero-Michael addition of a secondary alcohol to a tethered and Z-configured acrylate while aldehyde 21 was generated, in the crucial step of the relevant reaction sequence, via an Ireland-Claisen rearrangement reaction.
- Premraj, Rajaratnam,McLeod, Malcolm D.,Simpson, Gregory W.,Banwell, Martin G.
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p. 2949 - 2976
(2013/02/21)
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- Confirmation of the absolute configuration at C45 of amphidinol 3
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Amphidinol 3 (AM3), a membrane-active agent isolated from the dinoflagellate Amphidinium klebsii, consists of a long carbon chain containing 25 stereogenic centers. Although the absolute configuration of AM3 was determined by extensive NMR analysis and degradation of the natural product, the partial structure corresponding to the tetrahydropyran ring system was found to be antipodal to that of karlotoxin 2, a structurally related compound recently isolated from the dinoflagellate Karlodinium veneficum. By extensive degradation of the natural product and conversion of the resulting alcohol to an MTPA ester, the absolute configuration at C45 of AM3 was confirmed to be R, supporting the originally proposed structure.
- Manabe, Yoshiyuki,Ebine, Makoto,Matsumori, Nobuaki,Murata, Michio,Oishi, Tohru
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p. 2003 - 2006
(2013/02/22)
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- A [3+3] cyclization strategy for asymmetric synthesis of alkyl substituted piperidine-2-ones using 1,2-cyclic sulfamidates: A formal synthesis of (S)-coniine from l-norvaline
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Regioselective ring-opening reactions of a set of representative 1,2-cyclic sulfamidates with lithium triethylorthopropiolate proceeded efficiently to deliver the corresponding δ-amino-α,β-unsaturated esters after acidic hydrolysis. Hydrogenation of the unsaturated esters and subsequent thermal cyclization afforded the related alkyl substituted piperidine-2-ones. This approach represents a novel [3+3] cyclization strategy for the asymmetric synthesis of alkyl substituted piperidin-2-ones. Efficiency of the cyclization process is illustrated by a formal asymmetric synthesis of (S)-coniine from l-norvaline.
- Karanfil, Abdullah,Balta, Berrin,Eskici, Mustafa
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p. 10218 - 10229,12
(2020/09/02)
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- Rh(I)-catalyzed formal [6 + 2] cycloaddition of 4-allenals with alkynes or alkenes in a tether
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Rh(I)-catalyzed formal [6 + 2] cycloaddition of allenal 6 having an alkyne or alkene in a tether proceeded smoothly, giving 5-8- and 6-8-fused bicyclic ketone derivatives 7 in good to excellent yields. It was also found that cyclization of enantiomerically enriched (S)-6a (94% ee) gave cyclic ketone derivative (S)-7a in high yield with reasonable chirality transfer (86% ee). This result indicates that this cyclization proceeds through stereoselective formation of rhodacycle H′ followed by insertion of a multiple bond.
- Oonishi, Yoshihiro,Hosotani, Akihito,Sato, Yoshihiro
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supporting information; experimental part
p. 10386 - 10389
(2011/08/22)
-
- Enantioselective bioreduction of 2-fluoro-2-alken-1-ols mediated by Saccharomyces cerevisiae
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Biocatalytic reduction of 2-fluoro-2-alken-1-ols mediated by Saccharomyces cerevisiae underwent smoothly and yielded (S)-2-fluorinated alkanols with high enantioselectivities. The conversion rate was markedly depending on the configuration of alkene moiety of the substrate, the chain length of alkyl group at β position of CC bond, as well as the reaction conditions.
- Luo, Fan,Lu, Dengfu,Gong, Yuefa
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experimental part
p. 101 - 107
(2012/02/04)
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- Linked bis(β-diketiminato) yttrium and lanthanum complexes as catalysts in asymmetric hydroamination/cyclization of aminoalkenes (AHA)
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Linked bis(β-diketiminato) rare-earth metal complexes based on the ethylene-bridged ligand [C2H4(BDIDClP) 2]H2 [DClP = 2,6-Cl2C6H3] and the cyclohexyl-bridged ligands [Cy(BDIAr)2]H 2 [Ar = PMP (= p-MeOC6H4), Mes (= 2,4,6-Me 3C6H2), DIPP (= 2,6-iPr2C 6H3)] were prepared via amine elimination starting from [Ln{N(SiMe3)2}3] (Ln = La, Y). The three cyclohexyl-bridged complexes [{(R,R)-Cy(BDIMes)2} YN(SiMe3)2] ((R,R)-3), [{(R,R)-Cy(BDIMes) 2}LaN(SiMe3)2] ((R,R)-4), and [{(R,R)-Cy(BDIDIPP)2}LaN(SiMe3)2] ((R,R)-5) were obtained enantiomerically pure. The X-ray crystal structure analysis of the racemic variants of 3 and 4 revealed a distorted square pyramidal coordination geometry around the rare-earth metal, in which the amido ligand occupies the apical position and the two linked β-diketiminato moieties form the basis. The two aromatic substituents adopt a transoid arrangement and both β-diketiminato moieties are bound in a η5 coordination mode with close Ln?C contacts. Due to the smaller ionic radius of yttrium vs. lanthanum, the front side of the yttrium complex 3 is sterically more hindered than in the lanthanum complex 4, but there is much more empty coordination space on the rear side, which may rationalize the observed differences in selectivity of 3 in comparison to 4. The catalytic efficiency of the β-diketiminato complexes was strongly affected by steric factors such as ionic radius of the metal and the steric bulk of the aryl substituents, which is an indication for highly steric encumbered catalytic species. The complexes displayed good to moderate catalytic activity in the hydroamination/cyclization of aminoalkenes depending on the steric hindrance around the metal center. The sterically most demanding diisopropylphenyl- substituted complex (R,R)-5 displayed significantly higher enantioselectivities (up to 76% ee), but lower catalytic activity in comparison to the sterically more open mesityl-substituted complex (R,R)-4. The smaller yttrium metal center in complex (R,R)-3 led to reduced activity as well as a reversal in enantioselectivity, which may be rationalized by a change of the approach of the alkene moiety to the Ln-amido bond in the cyclization transition state.
- Vitanova, Daniela V.,Hampel, Frank,Hultzsch, Kai C.
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experimental part
p. 321 - 330
(2011/02/17)
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- Dynamic kinetic resolution during a vinylogous Payne rearrangement: A concise synthesis of the polar pharmacophoric subunit of (+)-scyphostatin
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"Chemical Equation Presented" The diastereomeric epoxycyclohexenols 3a/b (obtained via a Wharton rearrangement of a bis-epoxycyclohexanone precursor) were shown to undergo interconversion via a facile vinylogous Payne rearrangement. Mechanistic issues were probed; the doubly O-deuterated analogues underwent this equilibration more slowly than the parent dihydroxy compounds. It was possible to kinetically resolve the mixture of 3a/b under equilibrating conditions by use of Amano PS. This DKR is additionally noteworthy because it sets four stereocenters in a single event.
- Hoye, Thomas R.,Jeffrey, Christopher S.,Nelson, Dorian P.
-
supporting information; experimental part
p. 52 - 55
(2010/03/03)
-
- A biomimetic approach to the synthesis of a mycolic acid motif
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A new method for the stereoselective synthesis of the (R,R)-β-hydroxy-α-alkyl fatty acid fragment of mycolic acids, via an asymmetric anti-aldol reaction is reported. The 'mycolic acid motif' fragment was prepared in three steps and >98% ee.
- Driver, Cathryn H.S.,Balogun, Mohammed O.,Toschi, Gianna,Verschoor, Jan A.,Baird, Mark S.,Pilcher, Lynne A.
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supporting information; experimental part
p. 1185 - 1186
(2010/04/23)
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- Highly enantioselective bioreduction of 2-fluorocinnamyl alcohols mediated by Saccharomyces cerevisiae
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Biocatalytic reduction of 2-fluorocinnamyl alcohols mediated by Saccharomyces cerevisiae was investigated in phosphate buffer solutions. Product analysis clearly showed that (S)-2-fluoro-3-arylpropanols were afforded in high yields with up to 92% ee value.
- Luo, Fan,Wang, Ping,Gong, Yuefa
-
supporting information; experimental part
p. 1693 - 1695
(2010/04/29)
-
- Highly diastereoselective α-hydroxylation of fox chiral auxiliary-based amide enolates with molecular oxygen
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"Figure Presented" Using a trifluoromethylated oxazolidine (Fox) chiral auxiliary, the hydroxylation reaction of enolates was very efficiently performed under smooth and friendly conditions with molecular oxygen as oxidizer. This reaction occurred with an extremely high diastereoselectivlty. After cleavage, the chlral auxiliary Is efficiently recovered and highly valuable enantlopure oxygenated carboxylic acids and alcohols are released.
- Lubin, Hodney,Tessier, Arnaud,Chaume, Gregory,Pytkowicz, Julien,Brigaud, Thierry B.
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supporting information; experimental part
p. 1496 - 1499
(2010/07/03)
-
- Salts of Mosher's thioacid: agents for determining the enantiomer excess of SN2 substrates
-
The racemic and the (S)-enantiomer of Mosher's thioacid, 2-methoxy-2-trifluoromethylphenylacetic thioacid, form air-stable salts with Proton Sponge [1,8-bis(dimethylamino)naphthalene]. These salts are powerful nucleophiles that react cleanly (SN2 inversion) in CDCl3 with optically active alkyl halides ranging in reactivities from unactivated alkyl bromides and iodides to benzylic bromides. The diastereomeric excess (de) of the thioester products indicates the enantiomeric excess (ee) of the starting alkyl halides.
- Richman, Jack E.
-
supporting information; experimental part
p. 2793 - 2796
(2010/07/06)
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- Thioacids and thioacid salts for determining the enantiomeric excess of chiral compounds containing an electrophilic carbon center
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The invention provides novel chiral compounds including 2-methoxy-2-trifluoromethylphenylacetic thioacid useful to react with and analyze other chiral compounds that have an electrophilic chiral carbon center.
- -
-
Page/Page column 8-9
(2010/07/02)
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- Studies for the synthesis of xenicane diterpenes. A stereocontrolled total synthesis of 4-hydroxydictyolactone
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The stereocontrolled total synthesis of 4-hydroxydictyolactone (4), a member of the xenicane diterpene family of natural products, is described. These studies feature the development of the B-alkyl Suzuki cross-coupling reaction for direct access to (E)-cyclononenes from acyclic precursors. The Ireland-Claisen rearrangement is effectively utilized to establish the backbone asymmetry of the contiguous C2, C3, C10 stereotriad of 4. The synthesis strategy has devised an intramolecular Nozaki-Hiyama reductive allylation of a formate ester for the stereoselective formation of five-membered lactols 22. In addition, an internally directed SE′ propargylation using allenylmagnesium bromide is described to establish the stereochemistry of the C4 alcohol in 27, and the terminal alkyne is subsequently functionalized via a regioselective syn-silylstannylation to yield 30. Finally, the stereocontrolled phenylselenylation of the ester enolate derived from 43 leads to the desired syn-oxidative elimination to yield the natural product 4.
- Williams, David R.,Walsh, Martin J.,Miller, Nathan A.
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supporting information; experimental part
p. 9038 - 9045
(2009/12/04)
-
