Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol–carbene ligands

• Shohei Mimura,
• Sho Mizushima,
• Yohei Shimizu and
• Masaya Sawamura

Beilstein J. Org. Chem. 2020, 16, 537–543, doi:10.3762/bjoc.16.50

• % yield, with slightly lower enantioselectivity (Table 2, entry 2, 82% ee (S) vs 90% ee (R) in entry 1). The inversion of the absolute configuration of the product depended on the E/Z geometry of the substrates, and this was analogous to the reported results obtained with the chiral bisphosphine ligand

• UV detector, retention time = 9.1 min for the (R)-isomer and 13.3 min for the (S)-isomer). The absolute configuration of 2a was assigned by the comparison of the optical rotation with the same compound prepared by a reported method [4]. Proposed catalytic cycle. Optimization of the copper-catalyzed

Absolute configurations of talaromycones A and B, α-diversonolic ester, and aspergillusone B from endophytic Talaromyces sp. ECN211

• Ken-ichi Nakashima,
• Junko Tomida,
• Takao Hirai,
• Yoshiaki Kawamura and
• Makoto Inoue

Beilstein J. Org. Chem. 2020, 16, 290–296, doi:10.3762/bjoc.16.28

• first time in over 50 years. Keywords: absolute configuration; endophytic fungus; glauconic acid; Talaromyces; tetrahydroxanthone; xanthenedione; Introduction The xanthones, which are a class of phenolic compounds produced by many different organisms, including plants, lichens, fungi, and bacteria

• were presented. Furthermore, Nicolaou and Li introduced a means by which the absolute configuration can be determined from the total synthesis of α-diversonolic ester (3) [5]. However, to the best of our knowledge, data that enabled the determination of the absolute configuration has not been published

• . Nevertheless, the absolute configuration of aspergillusone B (4), which is a compound similar to α-diversonolic ester (3), had been determined by comparing the sign of its optical rotation with that of α-diversonolic ester (3) [6]. Therefore, the reported absolute configurations of 3 and aspergillusone B (4

Pigmentosins from Gibellula sp. as antibiofilm agents and a new glycosylated asperfuran from Cordyceps javanica

• Soleiman E. Helaly,
• Wilawan Kuephadungphan,
• Patima Phainuphong,
• Mahmoud A. A. Ibrahim,
• Kanoksri Tasanathai,
• Suchada Mongkolsamrit,
• Janet Jennifer Luangsa-ard,
• Souwalak Phongpaichit,
• Vatcharin Rukachaisirikul and
• Marc Stadler

Beilstein J. Org. Chem. 2019, 15, 2968–2981, doi:10.3762/bjoc.15.293

• -forming S. aureus. The structure elucidation and determination of the absolute configuration were accomplished using a combination of spectroscopy, including 1D and 2D NMR, HRMS, Mosher ester analysis, and comparison of calculated/experimental ECD spectra. A chemotaxonomic investigation of the secondary

• . Thus, the atropisomerism at the 6-6′ axis of pigmentosin A (1) was determined to be aR, while the absolute configuration of the stereogenic centers C-3/C-3′ remains unsolved. Compound 2 was obtained as pale green powder. The molecular formula of 2 was determined as C32H30O11 based on HRMS data. The 13C

• absolute configuration at C-12′of pigmentosin B (2), Mosher esters of 2 were prepared. The analysis of the ΔδSR values of the α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) esters were revealed to be negative (−0.07 for H-12′and −0.08/−0.05 for H2-11′), while positive ΔδSR values were observed for H3

Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

• Sara Tejera,
• Giada Caniglia,
• Rosa L. Dorta,
• Andrea Favero,
• Javier González-Platas and
• Jesús T. Vázquez

Beilstein J. Org. Chem. 2019, 15, 2881–2888, doi:10.3762/bjoc.15.282

• characterization process of glucosyl mono- and ditriazole derivatives, which we carried out in order to analyze the use of aryltriazoles for the determination of absolute configuration [15], we serendipitously discovered that these glucosyl ditriazoles led to gels. Therefore, we carried out the corresponding

Emission and biosynthesis of volatile terpenoids from the plasmodial slime mold Physarum polycephalum

• Xinlu Chen,
• Tobias G. Köllner,
• Wangdan Xiong,
• Guo Wei and
• Feng Chen

Beilstein J. Org. Chem. 2019, 15, 2872–2880, doi:10.3762/bjoc.15.281

• )-β-caryophyllene. However, since we have not performed chiral analysis, the absolute configuration of (E)-β-caryophyllene emitted from P. polycephalum plasmodia is still unknown. C) Mass spectra of unidentified terpenoids. P. polycephalum contains four terpene synthase genes. A) Multiple sequence

Nanangenines: drimane sesquiterpenoids as the dominant metabolite cohort of a novel Australian fungus, Aspergillus nanangensis

• Heather J. Lacey,
• Cameron L. M. Gilchrist,
• Andrew Crombie,
• John A. Kalaitzis,
• Daniel Vuong,
• Peter J. Rutledge,
• Peter Turner,
• John I. Pitt,
• Ernest Lacey,
• Yit-Heng Chooi and
• Andrew M. Piggott

Beilstein J. Org. Chem. 2019, 15, 2631–2643, doi:10.3762/bjoc.15.256

• strobilactone B, previously reported from A. ustus [29], with the only difference being hydroxylation at C-1 in 1, instead of at C-2. Therefore, the structure of 1 was assigned as shown in Figure 1. The absolute configuration of 1 was confirmed to be 1R,5S,6R,9R,13R by single crystal X-ray diffraction analysis

• reported in 2014 as an unnamed metabolite from Aspergillus sp. IBWF002-96 [5], and we have assigned the trivial name nanangenine B for consistency. The absolute configuration of 2 was assigned based on single crystal X-ray diffraction analysis of a 9-O-(4-bromobenzoyl) derivative (2b; Table S2 and Figure

• an unnamed metabolite (code number SF002-96-1) from Aspergillus sp. IBWF002-96 [4], and we have assigned the trivial name isonanangenine B for consistency. The absolute configuration of 3 was assigned based on single crystal X-ray diffraction analysis of a 1-O-(4-bromobenzoyl) derivative (3b; Table

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• of diarylprolinol silyl ethers is highly diastereoselective and that the configuration of a newly created stereocenter at the α-position depends predominantly on the catalyst structure. The absolute configuration of chiral 1,2-diols has been unambiguously established based on electronic circular

• preexisting stereochemical elements influence the stereoselectivity of this reaction. To this end we investigated α-photooxygenation of chiral aldehydes with a stereocenter at the β-position (Scheme 1). In such a case, the outcome should depend on the relationships between the absolute configuration of the

• stereoselectivity was enforced by bulkier and electron-withdrawing groups as diarylprolinol silyl ether 18 (Table 1, entries 4 and 5). The absolute configuration of diastereoisomers formed was assigned using chiroptical spectroscopic methods (see section ‘Determination of the absolute configuration of the product

Bipolenins K–N: New sesquiterpenoids from the fungal plant pathogen Bipolaris sorokiniana

• Chin-Soon Phan,
• Hang Li,
• Simon Kessler,
• Peter S. Solomon,
• Andrew M. Piggott and
• Yit-Heng Chooi

Beilstein J. Org. Chem. 2019, 15, 2020–2028, doi:10.3762/bjoc.15.198

• -13 were α-oriented. The absolute configuration of 1 was determined to be 1R,3R,6S,7R,13S by comparison of the experimental electronic circular dichroism (ECD) spectrum with time-dependent density functional theory (TDDFT)-calculated ECD spectra of the two possible enantiomers of 1 (Figure 4

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS)

• Philipp P. Könen and
• Matthias Wüst

Beilstein J. Org. Chem. 2019, 15, 1945–1961, doi:10.3762/bjoc.15.190

• cyclization takes place only from (S)-(−)-germacrene D, from which the absolute configuration of these substances can be derived. While the detected labeling patterns in our feeding experiments are in full agreement with the 1,3-hydride shift pathway, the cloning and functional characterization of the

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• both pairs of ethyl esters [26]. When a mixture of tert-butyl esters (2R,1'S)-5d and (2S,1'S)-5d was subjected to kinetic resolution in the presence of potassium tert-butoxide in tetrahydrofuran (2R,1'S)-5d was produced with low 40% de [27]. The absolute configuration at C2 in esters 5 was established

• nucleophiles to provide 9 or even by catalytic hydrogenation to form 10. Thus, biologically important fragments like vicinal amino alcohols 11 or 2-amino-1,3-propanediols 12a [Nu = OH] can be obtained in highly enantioselective procedures preserving the absolute configuration at C2. The latter compounds are

• ,1′R,1''S)-28 prepared from the aziridine aldehyde (2R,1′S)-6 which provided the 2R absolute configuration of the final product while the configuration at C1' was created by a stereoselective addition of phenylmagnesium bromide (Scheme 20) [29]. The aziridine ring opening in (2R,1′R,1''S)-28 with

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• due to the bulky chromophore introduced, and the resolution of the enantiomers was achieved due to the bulky size of the fluorophores. The absolute configuration of the enantiomers was determined by circular dichroism (CD) spectra. The solvent-induced aggregation behavior was investigated with the

• Sp configured isomer, based on calculations as well as single-crystal X-ray diffraction published recently [20]. Thus, the absolute configuration of the first fraction was assigned to be Sp and the second fraction was assigned to the Rp isomer. Unexpectedly, no induced CD signals of DPA units at 360

Efficient resolution of racemic crown-shaped cyclotriveratrylene derivatives and isolation and characterization of the intermediate saddle isomer

• Sven Götz,
• Andreas Schneider and
• Arne Lützen

Beilstein J. Org. Chem. 2019, 15, 1339–1346, doi:10.3762/bjoc.15.133

• they bear a chiral cavity that can be used for molecular recognition [19]. Probably the most famous example for this behavior is the chiral discrimination and determination of the absolute configuration of the two enantiomers of CHFClBr using an enantioenriched cryptophane-C [20][21]. Other examples

• also recorded and are shown in Figure 1. When we then started to examine the racemization behavior of 1 by heating solutions of (+)-(M)-1 and (−)-(P)-1 (assignment of the absolute configuration of the enantiomer according to the assignment of Collet and Gottarelli [62]) in EtOH to 78 °C and determining

• of (+)-(M)-1 and (−)-(P)-1 measured in CH3CN; black: first eluted enantiomer (+)-(M)-1 (c = 1.06 × 10−4 M), red: second eluted enantiomer (−)-(P)-1 (c = 1.03 × 10−4 M) (assignment of the absolute configuration of the enantiomer according to the assignment of Collet and Gottarelli [62]). a

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• sulfonylhydrazine 6 (1.2 equiv) in CH2Cl2 led to the desired N-tosylhydrazone 7 in 83% yield and with 82% ee (Scheme 3b). The absolute configuration was assigned on the basis of the structure of 7, which was confirmed unambiguously by an X-ray crystallographic study [39]. Tentative transition states to account for

Genomics-inspired discovery of massiliachelin, an agrochelin epimer from Massilia sp. NR 4-1

• Jan Diettrich,
• Hirokazu Kage and
• Markus Nett

Beilstein J. Org. Chem. 2019, 15, 1298–1303, doi:10.3762/bjoc.15.128

• yersiniabactin biosynthesis (Table S2, Supporting Information File 1), which led us to infer that the absolute configuration at C-19 is S. It was hence possible to predict the configuration of all stereocenters in 1 except C-15 by bioinformatics. To conclude the stereochemical analysis, we resorted to the NOESY

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• -ketosulfone 5a was carried out with moderate to high enantioselectivity but low diastereoselectivity and led to the formation of two diastereomers (2R,3S)-8a and (2S,3S)-9a. Since we did not succeed in growing a crystal that was suitable for X-ray determination of the absolute configuration of 8а, we defined

• the absolute configuration as compared to the analogous adamantyl derivative, which will be discussed below. It should be noted that low diastereoselectivity was previously observed in the asymmetric addition of various Michael donors to nitroalkenes in the presence of both metal complexes [47] and

• suitable for X-ray analysis were obtained for compound 8d (which is formed as an individual diastereomer). This made it possible to determine its absolute (2R,3S)-configuration, as well as to assign the absolute configuration for the other compounds obtained. The molecular structure of compound 8d is shown

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• significantly (>90:10, 17:18) if the reaction was maintained at −78 °C for several hours before quenching at that temperature, giving isolated yields of 30–50% for 17. The absolute configuration of 17 was based on the chemical correlation studies of Seebach [17][18][19] and of Pan [26] for benzylations, and

Phylogenomic analyses and distribution of terpene synthases among Streptomyces

• Lara Martín-Sánchez,
• Kumar Saurabh Singh,
• Mariana Avalos,
• Gilles P. van Wezel,
• Jeroen S. Dickschat and
• Paolina Garbeva

Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115

• culture headspace extracts by GC–MS [31]. Compound 4 was also isolated from in vitro incubations of FPP with the recombinant enzyme and its optical rotation was shown to be opposite to the material from Eucalyptus [32], but the absolute configuration remains unknown. Production of this sesquiterpene by S

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99

• , Supporting Information File 1). The absolute configuration of 1 was determined as the (+)-enantiomer, unanimously by optical rotary power measurement and an isotopic labelling strategy, which involved conversion of stereoselectively deuterated and at the same position 13C-labelled FPPs by the TS to yield

• most products. However, in the side product 7 C-1 remains untouched after 1,11-cyclisation, which allows to investigate the stereochemical course of the first cyclisation step for this compound. First, the absolute configuration of 7 was assigned as shown in Figure 2 from the incubation experiments

• HcS (Figure 7). The selective incorporation of deuterium into the diastereotopic positions of 7 is explainable by a 1Si,11Re-cyclisation of (R)-NPP. Given the absolute configuration of NPP and its formation via a 1,3-syn-allylic rearrangement from FPP, this ring closure represents an example of a

New terpenoids from the fermentation broth of the edible mushroom Cyclocybe aegerita

• Frank Surup,
• Florian Hennicke,
• Nadine Sella,
• Maria Stroot,
• Steffen Bernecker,
• Sebastian Pfütze,
• Marc Stadler and
• Martin Rühl

Beilstein J. Org. Chem. 2019, 15, 1000–1007, doi:10.3762/bjoc.15.98

• synthesis, we tentatively conclude a 2S,3R,8S,9R absolute configuration for pasteurestin C (4). The systematic name for 4 is (4S,4aR,7aS,7bR)-4-hydroxy-6,6,7b-trimethyl-2,4,4a,5,6,7,7a,7b-octahydro-1H-cyclobuta[e]indene-3-carboxylic acid. Bovistol A (1) showed weak cytotoxic effects (IC50 for L929 = 15 µg

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• can be partly separated. Their diastereoselectivities can be further enhanced by slow evaporation of the corresponding diastereomers from acetonitrile and the absolute configuration of one diastereomer was confirmed with X-ray crystal structure (Supporting Information File 1, Figure S2). After

• with TBAF. This racemate then underwent chiral resolution by reacting with (1S)-(−)-camphanic chloride to give a diastereomeric mixture of (R)-h or (S)-h. After separating these diastereomers by column chromatography, the absolute configuration of (S)-h was checked with its X-ray crystal structure

An efficient synthesis of the guaiane sesquiterpene (−)-isoguaiene by domino metathesis

• Yuzhou Wang,
• Ahmed F. Darweesh,
• Patrick Zimdars and
• Peter Metz

Beilstein J. Org. Chem. 2019, 15, 858–862, doi:10.3762/bjoc.15.83

• roots of Parthenium hysterophorus [5]. A recent enantioselective synthesis of (−)-isoguaiene (1) from (+)-dihydrocarvone [6] enabled an unambiguous assignment of its absolute configuration as depicted in Figure 1. Due to the structural similarity of 1 and the trisnorsesquiterpene clavukerin A (2), we

Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 789–794, doi:10.3762/bjoc.15.75

• stereochemical imprint of a TS on achiral products is not directly visible, there still can be a chiral cyclisation cascade behind these terpenes. This is true as well for examples featuring a mirror plane like the monoterpene 1,8-cineol (eucalyptol, 3), for which the absolute configuration of the intermediary

• cyclisation mechanism [27]. The absolute configuration of the intermediates nerolidyl diphosphate and the bisabolyl cation To address this question experimentally, (R)- and (S)-NPP were synthesised following a known route for enantioselective preparation of nerolidol [28] by Sharpless epoxidation of farnesol

• , the biosynthesis of 5 proceeds via two chiral intermediates, NPP and the bisabolyl cation (A), whereas the absolute configuration of the first was addressed experimentally by the synthesis and in vitro incubation of both enantiomers of NPP. These experiments clearly showed the involvement of (R)-NPP

Reusable and highly enantioselective water-soluble Ru(II)-Amm-Pheox catalyst for intramolecular cyclopropanation of diazo compounds

• Hamada S. A. Mandour,
• Yoko Nakagawa,
• Masaya Tone,
• Hayato Inoue,
• Nansalmaa Otog,
• Ikuhide Fujisawa,
• Soda Chanthamath and
• Seiji Iwasa

Beilstein J. Org. Chem. 2019, 15, 357–363, doi:10.3762/bjoc.15.31

• product in high yield with moderate enantioselectivity (Scheme 1, 2q). Similar results were obtained with trans-allylic diazo Weinreb amide derivatives bearing aliphatic substituents (Scheme 1, 2r and 2s). As shown in Figure S1 (Supporting Information File 1), the absolute configuration of product 2g was

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• found to possess optical purities identical to that of the parent substrate (S)-1f (ee = 99%) thereby confirming that complete chirality transfer occurred (from C4 to C2) during the [2,3]-sigmatropic rearrangement [33][34]. It is also worth mentioning that the absolute configuration of (Z)-3f and (E)-3f

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• a few steps into (2S,5'S)-tricholomic acid [47]. The absolute configuration of (R)-(−)-carnitine was established by enzymatic decarboxylation of (2S,3R)-3-hydroxyglutamic acid followed by exhaustive methylation [121]. Fluoroglutamic acids are of special interest for PET imaging [122] and among other