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

Asymmetric synthesis of a high added value chiral amine using immobilized ω-transaminases

• Antonella Petri,
• Valeria Colonna and
• Oreste Piccolo

Beilstein J. Org. Chem. 2019, 15, 60–66, doi:10.3762/bjoc.15.6

• substrate in aqueous media [25]. However, (R)-2 was obtained in 70% isolated yield and >99% ee. Finally, the product was converted into the corresponding dihydrochloride and compared with an authentic commercial sample in order to confirm the enantiomeric excess and absolute configuration. Conclusion

• racemic compound was used as reference. The absolute configuration was assigned by comparison of elution order of an authentic standard. General procedure for the transamination reaction with immobilized enzymes In a similar manner as previously described in [14], to 5 mL of a triethanolamine buffer (100

• boiling point byproduct acetone [2][3][4][5][6]. Since (R)- and (S)-selective TAs are available on the market, both enantiomers of the amine product are accessible. This point is particularly relevant since in most cases the pharmacological activity of a chiral drug is closely related to its absolute

N-Acylated amino acid methyl esters from marine Roseobacter group bacteria

• Hilke Bruns,
• Lisa Ziesche,
• Nargis Khakin Taniwal,
• Laura Wolter,
• Thorsten Brinkhoff,
• Jennifer Herrmann,
• Rolf Müller and
• Stefan Schulz

Beilstein J. Org. Chem. 2018, 14, 2964–2973, doi:10.3762/bjoc.14.276

• 7 and 8 (Scheme 2) that proved to be identical with the natural products. The absolute configuration of the amino acid could not be determined due to the low amount of material present. Nevertheless, because NAMEs showed the common -configuration [23], this configuration also seems likely for the

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• depending on the absolute configuration of the chiral auxiliary used. The aldehyde 5 was first prepared according to a described procedure in two steps from methyl L-lactate (Scheme 1) [31]. The reaction with (R)- or (S)-oxazolidinones 6 led to the formation of 2,3-syn aldol products 7 in good yields with a

Copolymerization of epoxides with cyclic anhydrides catalyzed by dinuclear cobalt complexes

• Yo Hiranoi and
• Koji Nakano

Beilstein J. Org. Chem. 2018, 14, 2779–2788, doi:10.3762/bjoc.14.255

• effect of linking two cobalt–salen complexes on the catalytic activity. The heterochiral complex (R,R,S,S)-1 demonstrated a much lower TOF of 237 h−1 than the homochiral one (R,R,R,R)-1 (Table 1, entry 6). Thereby, a combination of the same absolute configuration of two salen moieties was found to be

• favorable for a high catalytic activity. Such dependence of the catalytic activity on the absolute configuration contrasts with our previous observation in the epoxide/CO2 copolymerization where the heterochiral (R,R,S,S)-1 showed a much higher catalytic activity than the corresponding homochiral complex (R

• demonstrating dependence of the catalytic activity on the absolute configuration (Table 1, entries 10 and 12). However, the TOFs unexpectedly are much lower than those obtained by using (R,R,R,R)-1 and (R,R,S,S)-1. This trend was also observed for mononuclear complexes: the mononuclear complex rac-4 with fluoro

Stereoselective total synthesis and structural revision of the diacetylenic diol natural products strongylodiols H and I

• Pamarthi Gangadhar,
• Sayini Ramakrishna,
• Ponneri Venkateswarlu and
• Pabbaraja Srihari

Beilstein J. Org. Chem. 2018, 14, 2313–2320, doi:10.3762/bjoc.14.206

•  3) [32]. After derivatization and determination through Mosher’s ester analysis [33][34][35], the absolute configuration of the newly generated secondary hydroxy group-bearing carbon center (C6) was determined as R configuration (see Supporting Information File 1). The NMR analysis of the Mosher’s

• furnishing the chiral propargylic alcohol 25a with 92% ee (Scheme 5). After securing the absolute configuration at C6 in compound 25a by employing the Mosher’s ester analysis indicating S-configuration (see Supporting Information File 1), compound 25a was subjected to TBDPS protection followed by TBS

• propargyl alcohol involving 13 linear steps, respectively. Investigations towards exploring the current strategy for accessing other natural products and their analogues are currently underway. Proposed structures of a selection of diacetylenic polyol natural products. Absolute configuration analysis of

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases

• Maroš Bella,
• Sergej Šesták,
• Ján Moncoľ,
• Miroslav Koóš and
• Monika Poláková

Beilstein J. Org. Chem. 2018, 14, 2156–2162, doi:10.3762/bjoc.14.189

• absolute configuration of carbamate 20 was confirmed by single-crystal X-ray analysis (Figure 2) [36]. Basic hydrolysis of carbamate 20 with 10% NaOH in refluxing EtOH provided aminoalcohol 21 which was subsequently N-benzylated with the corresponding benzyl bromides to yield pyrrolidines 22. Final

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• ). Furthermore, the absolute configuration of 88 was assigned by its single crystal X-ray analysis. 3.3. Application of spirolactams in natural product synthesis In 2001, Ciufolini and co-workers [103] employed PIDA (15) as an electrophile during the synthesis of naturally occurring tricyclic azaspirane

• overall synthesis. The absolute configuration of the synthesised compound was determined by comparing the optical rotary values with that of natural compound (−)-aculeatin (146a) and (+)-aculeatin (146b). In the continuation to previous work, the same research group [136] reported the synthesis of

Copper-catalyzed asymmetric methylation of fluoroalkylated pyruvates with dimethylzinc

• Kohsuke Aikawa,
• Kohei Yabuuchi,
• Kota Torii and
• Koichi Mikami

Beilstein J. Org. Chem. 2018, 14, 576–582, doi:10.3762/bjoc.14.44

• methyl trifluoropyruvate (1b) instead of 1a resulted in a lower enantioselectivity (Table 1, entry 17). The absolute configuration of 2b was determined to be S by comparison with the optical rotation of reported data [32]. The absolute configurations of other alcohol products 2a and 2c–k were tentatively

Recent developments in the asymmetric Reformatsky-type reaction

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 325–344, doi:10.3762/bjoc.14.21

• actually 30-epiapratoxin E, thus correcting the originally proposed absolute configuration. Both diastereomers were tested for their antiproliferative activities in HCT116 cells, showing that natural (30R)-apratoxin E exhibited a higher activity than its (30S)-epimer. Due to their lower basicity, samarium

Volatiles from the tropical ascomycete Daldinia clavata (Hypoxylaceae, Xylariales)

• Tao Wang,
• Kathrin I. Mohr,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 135–147, doi:10.3762/bjoc.14.9

• compounds a synthesis of references was required. For one of the main compounds, 5-hydroxy-4,6-dimethyloctan-3-one, the relative and absolute configuration was determined by synthesis of all eight stereoisomers and gas chromatographic analysis using a homochiral stationary phase. Another identified new

• Pogostemon cablin (patchouli) [30], but is also known from fungal sources [31][32]. We show here the corrected structure as reported by Amand et al. [31], while for the compound from patchouli oil the opposite absolute configuration has been assigned [33]. The absolute configuration of 16 from Daldinia

• 11 were separable by GC on a homochiral stationary phase, one of which matched the natural product in terms of same retention times and mass spectra (Figure 3). To clarify the relative and absolute configuration of the natural stereoisomer of 11 an enantioselective synthesis was performed (Scheme 5

Polarization spectroscopy methods in the determination of interactions of small molecules with nucleic acids – tutorial

• Tamara Šmidlehner,
• Ivo Piantanida and
• Gennaro Pescitelli

Beilstein J. Org. Chem. 2018, 14, 84–105, doi:10.3762/bjoc.14.5

• spectrum, where molecular vibrational transitions occur (between 4000 and 750 cm−1) [3][36]. Recently, VCD has developed as a reliable spectroscopic method for the determination of the absolute configuration and conformational distribution of chiral molecules in solution [1][4][36]. The main drawback of

• richer in bands than a typical ECD spectrum (just like IR spectra vs UV–vis spectra) [1][4][36]. Nowadays, density functional theory (DFT) allows a calculation of the VCD spectrum of a chiral molecule, which then can be compared with the measured VCD spectrum and by this the absolute configuration (AC

Binding abilities of a chiral calix[4]resorcinarene: a polarimetric investigation on a complex case of study

• Marco Russo and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2017, 13, 2698–2709, doi:10.3762/bjoc.13.268

• absolute configuration assumed by the protonated N atom and the conformation of the arene–CH2–proline double free-rotating system, determine in turn the relative position of the negatively charged and bulky carboxylate group with respect to the macrocycle cavity (i.e., inwards or outwards). This provides a

Peptide synthesis: ball-milling, in solution, or on solid support, what is the best strategy?

• Ophélie Maurin,
• Pascal Verdié,
• Gilles Subra,
• Frédéric Lamaty,
• Jean Martinez and
• Thomas-Xavier Métro

Beilstein J. Org. Chem. 2017, 13, 2087–2093, doi:10.3762/bjoc.13.206

• (BM, solution and solid support) to the production of the VVIA peptide sequence, protected or not, depending on the strategy (all amino acids bearing L absolute configuration, Figure 1). The sequence has been chosen as it corresponds to the Aβ (39–42) tetrapeptide, a promising small therapeutic

18-Hydroxydolabella-3,7-diene synthase – a diterpene synthase from Chitinophaga pinensis

• Jeroen S. Dickschat,
• Jan Rinkel,
• Patrick Rabe,
• Arman Beyraghdar Kashkooli and
• Harro J. Bouwmeester

Beilstein J. Org. Chem. 2017, 13, 1770–1780, doi:10.3762/bjoc.13.171

• previously reported to have germacrene A synthase activity during heterologous expression in Escherichia coli, was identified by extensive NMR-spectroscopic methods as 18-hydroxydolabella-3,7-diene. The absolute configuration of this diterpene alcohol and the stereochemical course of the terpene synthase

• conversion of stereoselectively deuterated terpene precursors, because the problem of determining the absolute configuration of the terpene under investigation is simplified to a problem of delineating the relative orientation of its stereocentres to the known absolute configuration at the deuterated carbon

• [12][13]. This approach was used to determine the absolute configuration of 3 using both enantiomers of (R)- and (S)-(1-13C,1-2H)GGPP [14], (R)- and (S)-(1-13C,1-2H)FPP, and (R)- and (S)-(1-13C,1-2H)GPP [12] in which the additional 13C labels were introduced to increase sensitivity in the HSQC