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

• -triazol-1-yl)cyclohexanes 12 and 14, having the same configuration as compounds 7f and 8f, respectively, were analyzed. Both compounds formed gels, but the trans stereoisomer 12 did so only at a low temperature (8 °C) in DMSO (G = 1.1, w/w), similar to the β-anomer 7f, which possessed the same trans

• configuration. On the other hand, the cis stereoisomer 14 formed an opaque gel at room temperature in DMSO/H2O, 9:1, v/v (G = 0.8, w/w), showing a higher potency for gelation, similar to 8f. As such, this relationship mirrors the behavior observed for the 7f/8f pair. Table 2 also contains the different Tgs

• thin and short fibers. The xerogel of compound 12 showed long, thin, and relatively straight fibers, with lack of torsion, as well as regularity of the network. Its cis stereoisomer 14 showed a fibrous network, but of much shorter length. However, the gel of compound 10 showed a different morphology

Multiple threading of a triple-calix[6]arene host

• Veronica Iuliano,
• Roberta Ciao,
• Emanuele Vignola,
• Carmen Talotta,
• Patrizia Iannece,
• Margherita De Rosa,
• Annunziata Soriente,
• Carmine Gaeta and
• Placido Neri

Beilstein J. Org. Chem. 2019, 15, 2092–2104, doi:10.3762/bjoc.15.207

• ) [31][32][33][34][35][36][37]. Our group previously reported [17][18] some examples of directional threading of calix[6]-wheels [38] in which the endo-alkyl stereoisomer in Figure 9 is preferentially formed over the endo-benzyl one [17][18]. On the basis of these empirical observations, we have

• indicated by the presence in the 1H NMR spectrum of shielded alkyl resonances at negative value of chemical shift between −0.73 to −0.82 ppm. No evidence of the (endo-benzyl)-8+6 pseudo[2]rotaxane stereoisomer was detected in the 1H NMR spectrum of the 1:1 mixture of 8+ and 6. An ESI-FT-ICR mass spectrum

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• respect to the orthogonal plane of the axle, only one stereoisomer of the [6]rotaxane was obtained. Keywords: cucurbit[6]uril; cyclodextrin; macrocycles; mechanostereoisomer; rotaxane; Introduction Cyclodextrins (CDs) are macrocycles composed of glucoses linked via α-1,4-glycosidic bonds. CDs of six (α

• orientation, possibly due to inter-ring interactions with the CB[6], to give the [6]rotaxane as one single stereoisomer. Considering the ability of γ-CD to form stable 1:2 inclusion complexes, these singly threaded [n]rotaxanes could serve as an entry point to other high order interlocked structures by

• could be four possible orientations of the three interlocked γ-CD to give four different triazole environments (Figure 3b). Yet, only one of the four (isomer I or II) possible isomers has been observed in the 1H NMR, suggesting that 6R was obtained as a single stereoisomer. In fact, cooperative binding

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• of cis-indolylvinyl isonitrile, but also on the C-2, which is supressed in the presence of Mg2+ ions. AmbP3 transfers the dimethylallyl group on C-2 of hapalindole U in the reverse manner, but on C-2 of its C-10 stereoisomer in the normal manner. This review highlights the molecular bases of the

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

• Anthony Choi,
• Rebecca M. Morley and
• Iain Coldham

Beilstein J. Org. Chem. 2019, 15, 1480–1484, doi:10.3762/bjoc.15.149

• triethylamine and were pleased to obtain good yields of the adducts 7a–c and 8a,b (Scheme 2). In each case, the products 7a–c and 8a,b were formed as a single regioisomer and stereoisomer. The selectivity in favour of the isomer drawn in Scheme 2 was verified by single crystal X-ray analysis of the adduct 7c

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

• . Isolation of the product was then possible through repeated column chromatography. Similarly, the same group was also able to isolate the saddle stereoisomer of a chiral nonamethoxy-substituted CTV in which every arene unit carries three additional substituents through HPLC on a chiral stationary phase [27

• necessary to collect enough material to record sufficient 1H and 13C NMR spectra. The spectra were very similar to those published by Luz [26], thus verifying our assumption. Please note, that the saddle stereoisomer of a CTV undergoes very fast intramolecular pseudorotational motions to change between its

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• . The configuration of C-5 in each stereoisomer was established using NOESY experiments and theoretical models. The main limitation of this approach was the impossibility to incorporate both aromatic and sterically hindered amines (e.g., tert-butylamine). Besides the reports of Rivera’s and Ramírez’s

• components, keeping formaldehyde as oxo component to obtain a single stereoisomer. The library was also integrated by the Ugi-4CR products derived from the 6β-ecdystereoidal amine (also used as precursor of isocyanide 28), while all compounds were evaluated as antiproliferative agents against T-leukemia cell

Synthesis of a novel category of pseudo-peptides using an Ugi three-component reaction of levulinic acid as bifunctional substrate, amines, and amino acid-based isocyanides

• Maryam Khalesi,
• Azim Ziyaei Halimehjani and
• Jürgen Martens

Beilstein J. Org. Chem. 2019, 15, 852–857, doi:10.3762/bjoc.15.82

• . cIsolated yield of one of the diastereomers as pure stereoisomer after several recrystallization steps. ORTEP representation of compound (R*,S*)-4a with thermal ellipsoids at 50% probability. Opposite enantiomer is omitted for clarity. The atom numbering does not follow IUPAC nomenclature. Synthesis of

Synthesis of the aglycon of scorzodihydrostilbenes B and D

• Katja Weimann and
• Manfred Braun

Beilstein J. Org. Chem. 2019, 15, 610–616, doi:10.3762/bjoc.15.56

• exclusively, so that, after cleavage of the ester groups, epi-scorzodihydrostilbene D (13) was obtained as single stereoisomer (Scheme 4). Obviously, the conditions required in the glycosylation reaction – excess of the Lewis acid and elongated reaction time – resulted in the formation of the

A chemoenzymatic synthesis of ceramide trafficking inhibitor HPA-12

• Seema V. Kanojia,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2019, 15, 490–496, doi:10.3762/bjoc.15.42

• (HPA-12, 1, Figure 1) as the first inhibitor of CERT-mediated ceramide transport [11]. However, the initially determined (1R,3R) configuration of the most active HPA-12 stereoisomer (compound 1, Figure 1) was later revised to (1R,3S) configuration (compound 2, Figure 1) by Berkeš et al. in 2011 [12

• . However, after the structural revision of the most active stereoisomer, Kobayashi et al. synthesized (1R,3S)-HPA-12 (2, Figure 1) using a Zn-catalyzed asymmetric Mannich-type reaction in water, and unambiguously ascertained the revised configuration by X-ray crystallography [14]. The other syntheses of

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

• decomposition of this stereoisomer including racemization at Cα. From pentose via 2,3-aziridino-γ-lactone In the so called “2,3-aziridino-γ-lactone methodology” [18][99][100] ribose (or lyxose) is used as a starting material [101][102] which is transformed into the lactone 95 in several steps [99]. Boron

Synthesis of pyrrolidine-based hamamelitannin analogues as quorum sensing inhibitors in Staphylococcus aureus

• Jakob Bouton,
• Kristof Van Hecke,
• Reuven Rasooly and
• Serge Van Calenbergh

Beilstein J. Org. Chem. 2018, 14, 2822–2828, doi:10.3762/bjoc.14.260

• -closing metathesis of 24 now smoothly afforded 25 in high yield. Dihydroxylation selectively yielded the desired stereoisomer of diol 26, which was subsequently protected as isopropylidene acetal. In the next step, after removal of the TBS group and mesylation, attempted substitution with NaN3 resulted

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• catalysts, bicyclic lactone (±)-4 a stereoisomer of (±)-3 furnished olefinated γ-lactone (±)-6 similar to (±)-5 (Scheme 3, Table 2). Unfortunately, ROM reactions, however, took place with total conversions, they were always accompanied by the formation of a significant amount of polymeric materials (ROMP

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• H3B·P(n-C8H17)3 (1%), H3B·P((CH2)13CH2)(n-C8H17) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H3B·P((CH2)13CH2)((CH2)14)P((CH2)13CH2)·BH3 (6·2BH3, 10%), in,out-H3B·P((CH2)14)3P·BH3 (in,out-2·2BH3, 4%) and the stereoisomer

• upon independent syntheses from the dibridgehead diphosphines 2 obtained in Scheme 1 [6], they were assigned as in,out-2·2BH3 (4%) and the stereoisomer (in,in/out,out)-2·2BH3 (2%), as shown in Scheme 2. The depiction of the latter as an out,out (vs in,in) isomer in Scheme 2 is arbitrary, but represents

• rather tedious column chromatography: the dibridgehead diphosphine diborane in,out-2·2BH3, its constitutional isomer 6·2BH3, and its stereoisomer (in,in/out,out)-2·2BH3. It can be inferred from the top spectrum that the three products were the major components and moreover present in approximately equal

The enzymes of microbial nicotine metabolism

• Paul F. Fitzpatrick

Beilstein J. Org. Chem. 2018, 14, 2295–2307, doi:10.3762/bjoc.14.204

• the enzyme. While the dominant form of nicotine found in tobacco is (S)-nicotine, the (R)-stereoisomer is also found at detectable levels [22]. Nicotine dehydrogenase is reported not to be stereospecific, in that it can catalyze the hydroxylation of (R)-nicotine to (R)-6-hydroxynicotine; thus, this

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• stereoisomeric directional pseudo[2]rotaxanes, rotaxanes, and catenanes. Also in this case [38], we were able to obtain a stereoselective threading of the cone calix[6]arene-wheel with alkylbenzylammonium axles (Figure 4b), in which the endo-alkyl pseudo[2]rotaxane stereoisomer was the favoured one [38]. The

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

• to acid-catalyzed deprotection with H2SO4@SiO2 (25 wt % [33] as depicted in Scheme 3). Alcohol 1i, was recovered as a single stereoisomer, identical to the commercially available starting material, as determined by 1H and 13C NMR analysis of the crude reaction mixture (see Supporting Information File

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• %) along with the N7 stereoisomer (10%). These results support the above-mentioned hypothesis. Finally, 4'-thioadenosine (49) was synthesized by treating 45 with TFA followed by methanolic ammonia [46] (Scheme 5). The same group attempted to apply the oxidative coupling reaction to the synthesis of

Volatiles from three genome sequenced fungi from the genus Aspergillus

• Jeroen S. Dickschat,
• Ersin Celik and
• Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

• from cantaloupe a structural revision to the Z stereoisomer is proposed. Ethyl (Z)-hept-4-enoate also occurs in Aspergillus clavatus and was identified by synthesis of an authentic standard. Keywords: Aspergillus; GC–MS; genomics; terpenes; volatiles; Introduction Ascomycete fungi are a highly

•  2 and Scheme 4). In addition, small amounts of the sesquiterpenes β-elemene (21a), germacrene D (22), β-ylangene (23) and its stereoisomer β-copaene (24) were found. All these sesquiterpenes require a 1,10-cyclisation of FPP to the (E,E)-germacradienyl cation (N). Its deprotonation leads to

• from cantaloupe (Curcumis melo) and tentatively identified as ethyl (E)-hept-4-enoate [44], but the E stereoisomer should elute significantly later than the Z isomer. Likely, the reported compound is the same as found here and the structure requires correction to ethyl (Z)-hept-4-enoate. Further ethyl

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

• 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

Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity

• Tathagata Mukherjee,
• Soumik Biswas,
• Andreas Ehnbom,
• Subrata K. Ghosh,
• Ibrahim El-Zoghbi,
• Nattamai Bhuvanesh,
• Hassan S. Bazzi and
• John A. Gladysz

Beilstein J. Org. Chem. 2017, 13, 2486–2501, doi:10.3762/bjoc.13.246

• helical chiralities (see Figure S2, Supporting Information File 1), affording a meso stereoisomer. Finally, attempts have been made to extend the preceding chemistry in several directions. In screening experiments, all of the fluorous iodine(III) dichlorides assayed, as well as PhICl2, were competent for

Fluorination of some highly functionalized cycloalkanes: chemoselectivity and substrate dependence

• Attila Márió Remete,
• Melinda Nonn,
• Santos Fustero,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2017, 13, 2364–2371, doi:10.3762/bjoc.13.233

• protocol compound (±)-3 was obtained in a modest yield (15%) that could be slightly increased to 25% by the addition of DBU to the reaction mixture (Scheme 1). In contrast to (±)-1, its stereoisomer (±)-4, afforded in the reaction with 1.5 equiv of Deoxofluor in the presence of 4 equiv of DBU, according to

• the base the yields of (±)-10 and (±)-11 decreased to 10% and 17%, respectively. Unfortunately and surprisingly, diol (±)-12 (derived from trans-2-aminocyclohex-4-ene carboxylic acid) [23][24][25][26] a stereoisomer of (±)-8, in the reaction with either 1 equiv or excess of Deoxofluor did not give any

• identifiable product. However, according to earlier observations on the effect of DBU the reaction in the presence of this base afforded keto ester (±)-13 in 41% yield. In contrast to the stereoisomer (±)-8, reaction of diol (±)-12 with Deoxofluor took place at the C-5 hydroxy group leading to intermediate T11

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

• stereoisomer. Then, if the carbon chain of 8 could be extended by one atom to give the homologated aldehyde 9, fluorination could be repeated and the cycle could continue until the desired number of fluorine atoms was installed. This hypothetical approach had several attractions, including (i) the flexibility

• of being able to generate amino acids of different backbone lengths (e.g., 5, 6, Figure 1) via a unified strategy; (ii) an ability to access any stereoisomer of the target molecules (provided that the stereoselectivity in each fluorination step was catalyst-controlled); (iii) the lower toxicity of

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• the homogeneous products are trans-configured. This assumption is supported by the results obtained with cyclopentadiene and both E- and Z-1b [32]. Whereas the reaction with E-1b led to only one stereoisomer, in the case of Z-1b, exo- and endo-isomers with preserved cis-orientation of the CN and CO2Me

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• intermediate 45, which was subjected to Wittig olefination. Subsequent aza-Sakurai cyclization of intermediate 46 provided tricyclic derivative 47 as a single stereoisomer, which was then transformed into target myrioneurinol by standard operations. Addition of organometallic reagents to conjugated