Fabclavine diversity in Xenorhabdus bacteria

• Sebastian L. Wenski,
• Harun Cimen,
• Natalie Berghaus,
• Sebastian W. Fuchs,
• Selcuk Hazir and
• Helge B. Bode

Beilstein J. Org. Chem. 2020, 16, 956–965, doi:10.3762/bjoc.16.84

• reductase, Nit: nitrilase, A: adenylation, C: condensation, E: epimerization, TP: transport. Comparison of the fcl BGCs in Xenorhabdus and Photorhabdus strains responsible for the fabclavine biosynthesis. a: X. szentirmaii, b: X. budapestensis, c: X. cabanillasii, d: X. indica, e: X. hominickii, f: X

• , A: adenylation, C: condensation, E: epimerization, TP: transport. Compound list of the fabclavine derivatives identified in this work. The structures are based on MALDI–HRMS and MALDI–MS2 analyses using the known structure of 1 as a reference [20]. The derivatives 1–4 and 17–22 were described

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• . Systematic kinetic studies using NMR experiments suggested that protonation of the intermediate 252 occurs from the sterically favored side, leading to the kinetically stable cis product (Scheme 42). Nonetheless, some epimerization under the reaction conditions took place leading to the thermodynamically

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

• Lukáš Kerner and
• Paul Kosma

Beilstein J. Org. Chem. 2020, 16, 9–14, doi:10.3762/bjoc.16.2

• -benzyl-protected gluco and galacto derivatives [20][27][30][31]. In addition to exocyclic glycals mimicking putative planar transition states of substrates involved in enzymatic reactions, such as glycosyl transfer, mutase, and epimerization, endo-glycals are also of interest [21][22][32][33][34][35

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

• -phenylethyl group]. As the closest analogues of Garner’s aldehyde (3a) and other chiral α-aminoaldehydes, e.g., 4, or aziridine aldehydes 6 do not undergo epimerization during preparation as well as in further transformations conducted in the presence of basic reagents because of the high barrier to inversion

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• relationship between the starting oxirane and the enyne product was always obtained, whatever the group transferred from boron to the oxirane carbon. These results revealed the stereospecificity of the reaction and suggested that no epimerization of the oxiranyllithium intermediate occurred. The present

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

• bioinformatics as well as spectroscopy. First, we analyzed whether the isolated natural product possesses a D- or L-configured thiazoline ring. Previous studies had revealed that the D-thiazoline ring in pyochelin is due to an unusual methyltransferase-like epimerization domain in the biosynthesis protein PchE

• , fatty acyl-AMP ligase; ACP, acyl carrier protein; KS, β-ketoacyl synthase; AT, acyltransferase; KR, ketoreductase; C, condensation; A, adenylation; MT, methyltransferase; PCP, peptidyl carrier protein; TE, thioesterase. The asterisk indicates a methyltransferase-like epimerization domain. C) UV

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

• , and, on the other hand, the ratio of diastereomers in the presence of the same catalyst strongly depends on the solvent used. This suggests that the dr is determined by the rates ratio of the catalytic reaction (which can occur with high or low diastereoselectivity) and the epimerization of products

• (8a:9a) reached 6.3:1, while the conversion is 82%. After 50 hours, the dr reached 3:1, while the reaction practically stopped. Further, we carried out a control experiment to evaluate the epimerization rate of product 8a in solution under the same conditions. For this purpose the individual

• diastereomer 8a was dissolved in chloroform-d and the formation of the second diastereomer 9a was monitored by 1H NMR. Surprisingly, we found that, along with the epimerization of (2R,3S)-8a to (2S,3S)-9a, retro-Michael reaction occurred (Figure 4). It is noteworthy that firstly the formation of sulfone 5a was

Synthesis of (macro)heterocycles by consecutive/repetitive isocyanide-based multicomponent reactions

• Angélica de Fátima S. Barreto and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2019, 15, 906–930, doi:10.3762/bjoc.15.88

• obtained as a diastereomeric mixture via an Ugi–Nenajdenko reaction using the 4-methyl-2,6,7-trioxabicyclo[2,2,2]octyl (OBO) ester 46 to avoid epimerization of the isocyanide, followed by a reductive amination and chromatographic separation of the isomers; a Passerini–Dömling IMCR led to the heterocyclic

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• tert-butyl ester 13a to the alcohol by portionwise addition of DIBAL and careful temperature control (slow warm-up from −78 to −30 °C) afforded the alcohol without α-epimerization, which was oxidized to aldehyde 15 (IBX, Scheme 3). Adamantyl ester 14 resisted reduction under the same conditions and was

Synthesis and biological investigation of (+)-3-hydroxymethylartemisinin

• Toni Smeilus,
• Farnoush Mousavizadeh,
• Johannes Krieger,
• Xingzhao Tu,
• Marcel Kaiser and
• Athanassios Giannis

Beilstein J. Org. Chem. 2019, 15, 567–570, doi:10.3762/bjoc.15.51

• , whereas the desired (+)-3-hydroxymethylartemisinin (2) was produced from 17 in two steps including epimerization and cleavage of the TES group in excellent yield (Scheme 3). Finally, we evaluated the antimalarial activity of (+)-3-hydroxymethylartemisinin (2) as well as of the derivatives 16 and 18

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• ] were not able to reproduce the deprotection of the benzoylated derivative 8b as described in the work of Mikhailopulo et al. [26]. Instead, they observed a substantial epimerization leading to a ca. 2:1 mixture of the β/α anomers of NR+Br− and recommended the use of 1,2,3,5-tetra-O-acetyl-β-D

Green synthesis of new chiral 1-(arylamino)imidazo[2,1-a]isoindole-2,5-diones from the corresponding α-amino acid arylhydrazides in aqueous medium

• Nadia Bouzayani,
• Jamil Kraїem,
• Sylvain Marque,
• Yakdhane Kacem,
• Abel Carlin-Sinclair,
• Jérôme Marrot and
• Béchir Ben Hassine

Beilstein J. Org. Chem. 2018, 14, 2923–2930, doi:10.3762/bjoc.14.271

• state becomes unlikely and then the selectivity is important. Our model is in agreement with the diasteroisomeric ratio results. In fact, a total diastereoselectivity was observed, including 5d (R = Ph) since an epimerization of the initial asymmetric center was observed, therefore racemic trans-isomers

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• McMurry coupling to the diol, followed by two-step epimerization at C2. Assembly of the envisaged cyclization precursor 27. Structure analysis of diastereomeric cyanohydrins 29 and 30. Formation of allenes 32 and 34 from sterically crowded propargylic alcohol 31. Supporting Information Supporting

Heterogeneous acidic catalysts for the tetrahydropyranylation of alcohols and phenols in green ethereal solvents

• Ugo Azzena,
• Massimo Carraro,
• Gloria Modugno,
• Luisa Pisano and
• Luigi Urtis

Beilstein J. Org. Chem. 2018, 14, 1655–1659, doi:10.3762/bjoc.14.141

• -isopropyl-5-methylcyclohexanol ((−)-menthol, 1i). The reaction afforded an almost 1:1 mixture of only two diastereoisomers as determined by 1H and 13C NMR analysis of the crude reaction mixture, thus suggesting that it occurs with no epimerization at C1. This result was confirmed by submitting compound 3i

Lanyamycin, a macrolide antibiotic from Sorangium cellulosum, strain Soce 481 (Myxobacteria)

• Lucky S. Mulwa,
• Rolf Jansen,
• Dimas F. Praditya,
• Kathrin I. Mohr,
• Patrick W. Okanya,
• Joachim Wink,
• Eike Steinmann and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 1554–1562, doi:10.3762/bjoc.14.132

• lanyamycin epimers 1 and 2 mainly were observed in the side chains of the 16 membered macrolactone. As consequence of the epimerization, the conformation of the amide part of the side chain was adjusted. Particularly, the methyl group C-43 next to the epimeric centre was shifted from 0.87 ppm to higher field

Synthesis of a sucrose-based macrocycle with unsymmetrical monosaccharides "arms"

• Karolina Tiara,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2018, 14, 634–641, doi:10.3762/bjoc.14.50

• to Vasellas' procedure [31][32] – with benzylamine under the reductive amination conditions afforded an inseparable mixture of two products differing in the configuration at the C2 center (12a and 12b; Scheme 2); such a phenomenon – epimerization under these conditions – is known [33]. The

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• several research groups to focus their attention on the development of biotransformations with non-pathogenic, easy-to-manage microorganisms, and their enzymes. In particular, the enzymatic reactions involved are selective hydrolysis, epimerization of the hydroxy functions (by oxidation and subsequent

• in this review. C12 Dehydroxylation Chemical dehydroxylation UDCA can be obtained by a multistep chemical synthesis starting from CA. Two main steps are involved: the dehydroxylation at C12 and the epimerization of the 7-OH group. In order to achieve chemical dehydroxylation, firstly CA has to be

• ]. Biocatalytic C12 dehydroxylation In contrast to the reports on the epimerization of CA and CDCA with enzymes (see below ”Enzymes for the production of UDCA from CDCA”), the dehydroxylation of CA remains an undiscovered field for microbiologists and biochemists. To our knowledge, the only evidence of a

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• material to confirm that the process did not induce any epimerization. This methodology was then extended to the synthesis Gly-ψ[(E)-CF=CH]-Gly (not shown). Finally, Dory and co-workers reported the synthesis of Fmoc-Gly-ψ[(Z)-CF=CH]-Phe (Scheme 9) [36].Their work was inspired by the methodology reported

• -Ser-Phe-Arg-Phe-NH2 and Gly-ψ[(E)-CF=CH]-Gly-Phe-Ser-Phe-Arg-Phe-NH2 (see Scheme 7), representing the seven last amino acids of the neuropeptide 26Fra [34]. For the analogue containing the Gly-ψ[(Z)-CF=CH]-Phe isostere, epimerization was observed during last stages of the synthesis. The two

• isomerization or epimerization, cyclic pseudopeptides using Fmoc SPPS [48][50]. Biological studies were conducted on monofluoroalkene-containing analogues of FC131, which is a known antagonist of the chemokine receptor CXCR4. The latter has implications in cancer metastasis and HIV 1 infection. Anti-HIV 1

A permutation approach to the assignment of the configuration to diastereomeric tetrads by comparison of experimental and ab initio calculated differences in NMR data

• Przemysław J. Boratyński

Beilstein J. Org. Chem. 2017, 13, 2478–2485, doi:10.3762/bjoc.13.245

• 1 and 2 were obtained by epimerization at C9. Mixtures of the isomers of 1 were formed in TBAF desilylation of Cinchona 4-TMS-triazole derivatives. Partial isomerisation of 2a into 2b was performed by transient deprotonation using in situ generated sodium methylsulfinylmethylide (Scheme 1). Both

Hydrolysis, polarity, and conformational impact of C-terminal partially fluorinated ethyl esters in peptide models

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2017, 13, 2442–2457, doi:10.3762/bjoc.13.241

• partial epimerization of the residue. Finally, ester 4 was prepared by treatment of 6 with 3 equivalents of the 2,2-difluorodiazoethane (Scheme 1C). The reaction was performed smoothly using chloroform as a solvent giving a good yield (94%). We also attempted to perform the reaction in an acetonitrile

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• amino acid analogues [22][23]. However, epimerization in the α-position frequently occurs under the alkaline reaction conditions of the Seyferth–Gilbert and the Corey–Fuchs reaction. In order to access propargylamines with modified side chains, we chose a de novo synthesis strategy, using Ellman’s

• ], it provides a versatile protective group for the amine during the conversion of the alkyne. Additionally, it’s chirality indicates epimerization and, for example in the Pauson–Khand reaction [14], allows the determination of the stereoselectivity of asymmetric conversions by simple 1H NMR experiments

Synthesis of ergostane-type brassinosteroids with modifications in ring A

• Vladimir N. Zhabinskii,
• Darya A. Osiyuk,
• Yuri V. Ermolovich,
• Natalia M. Chaschina,
• Tatsiana S. Dalidovich,
• Miroslav Strnad and
• Vladimir A. Khripach

Beilstein J. Org. Chem. 2017, 13, 2326–2331, doi:10.3762/bjoc.13.229

• the epimerization of the hydroxy group at C-2/C-3 is the inactivation process contributing to a constant level of the active phytohormone. 2β,3β-Diols 6 are available through Woodward–Prévost cis-dihydroxylation of Δ2-steroids 3 [21]. The diaxial diols 7 can be easily synthesized by an acid-catalyzed

Homologated amino acids with three vicinal fluorines positioned along the backbone: development of a stereoselective synthesis

• Raju Cheerlavancha,
• Ahmed Ahmed,
• Yun Cheuk Leung,
• Aggie Lawer,
• Qing-Quan Liu,
• Marina Cagnes,
• Hee-Chan Jang,
• Xiang-Guo Hu and
• Luke Hunter

Beilstein J. Org. Chem. 2017, 13, 2316–2325, doi:10.3762/bjoc.13.228

• next deoxyfluorination reaction (Scheme 4). Gratifyingly, the p-nitro group of 39a was found to completely shut down the neighbouring group participation pathway; the desired trifluoroalkane 40a was obtained in good yield with no evidence of rearrangement or epimerization. It was also possible to

A mechanochemical approach to access the proline–proline diketopiperazine framework

• Nicolas Pétry,
• Hafid Benakki,
• Eric Clot,
• Pascal Retailleau,
• Farhate Guenoun,
• Fatima Asserar,
• Chakib Sekkat,
• Thomas-Xavier Métro,
• Jean Martinez and
• Frédéric Lamaty

Beilstein J. Org. Chem. 2017, 13, 2169–2178, doi:10.3762/bjoc.13.217

• the presence of EDC (coupling agent), a base and a small amount [29] of EtOAc as liquid grinding assistant. The role of oxyma was mainly to suppress amino acid epimerization during the coupling, a limited problem in the case of proline. Consequently, our first experiments did not involve this reagent

• it would avoid a potential pressure build-up (release of CO2) which could occur with NaHCO3. Noteworthy, no epimerization could be detected by NMR or HPLC analyses. Both peptides 7 and 8 were then deprotected and cyclized into the corresponding diketopiperazine 9. Palladium-catalyzed hydrogenolysis

Phenylsilane as an effective desulfinylation reagent

• Wanda H. Midura,
• Aneta Rzewnicka and
• Jerzy A. Krysiak

Beilstein J. Org. Chem. 2017, 13, 1513–1517, doi:10.3762/bjoc.13.150

• 4 under conditions used by us before, i.e., by treatment with isopropylmagnesium chloride, gave a mixture of diastereomers 7a and 7b. It was probably due to epimerization on carbon C2 of the carbanion, formed after attack of the Grignard reagent on sulfur. To our satisfaction, utilization of the

• desulfinylation process leading to ester 11 [24]. Unfortunately in this case the stereogenic center at the carbon undergoes epimerization under these reaction conditions and 11 is obtained in racemic form. To study the scope and limitation of the silane reactivity and its selectivity we checked the influence of