Nonenzymatic synthesis of anomerically pure, mannosyl-based molecular probes for scramblase identification studies

• Giovanni Picca,
• Markus Probst,
• Simon M. Langenegger,
• Oleg Khorev,
• Peter Bütikofer,
• Anant K. Menon and
• Robert Häner

Beilstein J. Org. Chem. 2020, 16, 1732–1739, doi:10.3762/bjoc.16.145

• pure MPC-2 (see Supporting Information File 1). As shown in Figure 3, the acetylated mannose phosphoramidite β-4Ac-Man-CEP was coupled to the free hydroxy group of the citronellol derivatives containing the functional tags (Cit-BZP-yne or Cit-Dod-NBD). The reactions were performed in dichloromethane

Synthesis of the tetrasaccharide repeating unit of the O-specific polysaccharide of Azospirillum doebereinerae type strain GSF71^T using linear and one-pot iterative glycosylations

• Arin Gucchait,
• Pradip Shit and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2020, 16, 1700–1705, doi:10.3762/bjoc.16.141

• elongation C-3 hydroxy group in the ʟ-rhamnosyl thioglycoside donor 3 allowed carrying out the stereoselective glycosylation steps followed by the removal of the PMB group [25] in one pot. This was achieved by using a combination [26][27][28][29][30] of N-iodosuccinimide (NIS) and perchloric acid supported

• treatment with HClO4-SiO2 [34]; (c) selective acetylation of the primary hydroxy group, and (d) removal of the benzyl groups by catalytic transfer hydrogenation [35] using triethylsilane in the presence of Pearlman’s catalyst [36] to furnish the desired tetrasaccharide 1 in 50% overall yield with the two O

Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens

• Sharavathi G. Parameswarappa,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140

• was modified into compound 6 via benzylidene ring opening followed by benzoylation of the free C-4 secondary hydroxy group in 27. The disaccharide imidate 29 was synthesized from 6 by anomeric desilylation to afford 28 that was converted to the corresponding imidate in an excellent yield. The final [2

Antibacterial scalarane from Doriprismatica stellata nudibranchs (Gastropoda, Nudibranchia), egg ribbons, and their dietary sponge Spongia cf. agaricina (Demospongiae, Dictyoceratida)

• Cora Hertzer,
• Stefan Kehraus,
• Nils Böhringer,
• Fontje Kaligis,
• Robert Bara,
• Dirk Erpenbeck,
• Gert Wörheide,
• Till F. Schäberle,
• Heike Wägele and
• Gabriele M. König

Beilstein J. Org. Chem. 2020, 16, 1596–1605, doi:10.3762/bjoc.16.132

• together with the 13C NMR data, giving evidence for one C–C and two C–O double bonds, thus suggested a structure with six rings. The presence of a hydroxy group and ester functionalities was deduced from characteristic IR absorptions at 3416, 1732 and 1234 cm−1 (Supporting Information File 1) [39][40][53

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts

• Soundararajan Karthikeyan,
• Radha Krishnan Shobana,
• Kamarajapurathu Raju Subimol,
• J. Helen Ratna Monica and
• Ayyanoth Karthik Krishna Kumar

Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130

• protection and elimination of the allylic hydroxy group. We believe that this crucial strategy could be primarily resolved by a quaternary phosphonium salt. After the initial screening of various quaternary phosphonium salts, the azidophosphonium salt [Ph3P+CBr3]N3−, reported by Blanco and co-workers, was

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• alcohol by the thiyl radical produces thiophenol and an allylic radical. Next, the single-electron transfer (SET) from the allylic radical to another thiyl radical generates the allylic cation. Subsequently, the proton abstraction from the hydroxy group by the SET-generated thiolate gives the final

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• -unsubstituted 2,3-dihydroisoxazoles in moderate to very good yields, starting from readily available 5-acetoxy- and 5-hydroxyisoxazolidines [7][8]. Their reactivity in electrophilic addition reactions allows for a straightforward introduction of a hydroxy group at the C-4 position of the resulting

• hydroborations proceeded with the exclusive formation of isoxazolidines with a hydroxy group in the C-4 position. We assume that the excellent regioselectivity is unambiguously caused by electronic effects since the endocyclic oxygen atom donates electrons to the C=C double bond, developing a negative partial

• 8b resulted only in a reductive cleavage of the N–O bond. A successful debenzylation was achieved in a two-step procedure using 2,2,2-trichloroethyl chloroformate (TrocCl). However, the protection of the hydroxy group was required first (for the reaction of 8b with benzoyl chloride, see Supporting

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• the esters 83 with boronic acids 84a,b afforded the substituted phenylalanine derivatives 85a,b, respectively [58]. Deprotection of the hydroxy group was achieved by treatment with TBAF in THF to give 86a,b. Finally, fluorination of the alcohols 86a,b with DAST followed by deprotection gave the

• the primary hydroxy group (Alloc) gave alcohol 117 in good yield. The fluorination of 117 was achieved by treatment with DAST to form 118. Then, selective removal of the Alloc protecting group using Pd(PPh3)4, was followed by oxidation of the resulting Boc-protected amino alcohol 119 to give the N-Boc

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

• Dong Cai,
• ZhiHua Zhang,
• Yufan Meng,
• KaiLi Zhu,
• LiYi Chen,
• ChangXiang Yu,
• ChangWei Yu,
• ZiYi Fu,
• DianShen Yang and
• YiXia Gong

Beilstein J. Org. Chem. 2020, 16, 798–808, doi:10.3762/bjoc.16.73

• instance, the hydroxy group can be converted into an oxime, acyloxyimino, alkoxyimino, alkoxy and 3-oxo group [9]. As a proteasome inhibitor, compound a suppresses the chymotrypsin-like activity of the proteasome in MT4 cells with an IC50 of 0.22 μM, nearly 100-fold more potent than 18β-glycyrrhetinic acid

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

• -additions of cuprates derived from a silyllithium [47] to α,β-unsaturated ketones [48]. There was no effort made at that time to convert these reactions to the corresponding catalytic processes, rather, the accent was more towards using the silyl group introduced as a hydroxy group equivalent [49][50][51

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

• diethoxymethylsilane (4 equiv) as a reductant and t-AmOH (1 equiv) as a protonation reagent in DMA as the solvent at 25 °C for 15 h, the product 2a was produced in 98% yield (1H NMR analysis) with a promising enantioselectivity of 69% ee (Table 1, entry 1). When the phenolic hydroxy group of L1 was changed to a

• ). Thus, the hydroxy group of L1 was essential for the enantioselectivity by the catalyst. When the mesityl group of L1 was changed to a bulkier 2-Me-4,6-Cy2-C6H2 group in L4, the enantioselectivity was markedly improved to 90% ee, with a high yield (97%, Table 1, entry 4). A naphthol substituent on the

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• and the carbohelicene moieties (Scheme 1) [16]. The approach focused on the regioselective one-pot synthesis of a 7-hydroxybenzo[b]phosphole derivative from an 3-alkoxyphenylzinc reagent, an alkyne, and dichlorophenylphosphine [17]. The hydroxy group of this key intermediate served as a handle for the

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

• Anna R. Bockman and
• Jeffrey M. Pruet

Beilstein J. Org. Chem. 2020, 16, 509–514, doi:10.3762/bjoc.16.46

• compared to a benzyl substituent [18]. The deleterious effect of a substituent α to the amine was most pronounced in the case of alanine (product 13), as compared to glycine (product 2). However, this steric constraint could be largely overcome by the presence of a β-hydroxy group, as seen with serine

• (product 5). For β-hydroxyamines it is expected the hydroxy group expedites the amidation via hydrogen bonding to the 7-CMP carbonyl group, to assist in bringing the amine nucleophile into place (Figure 2). Quite unsurprisingly, secondary amines were less reactive, with N-methylbenzylamine (for 16) being

• entirely unreactive under the typical reaction conditions. In this case the reaction required 3 h at 130 °C before product formation was observed. Interestingly, much like the improved results for serine, a β-hydroxy group dramatically overcame this issue for secondary amines, as 2-(methylamino)ethanol

Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Brønsted acidic ionic liquid

• Fei You,
• Xing He,
• Song Gao,
• Hong-Ru Li and
• Liang-Nian He

Beilstein J. Org. Chem. 2020, 16, 351–361, doi:10.3762/bjoc.16.34

• attached to the hydroxy group while in the corresponding ester product (l2–10, Figure 1), C12 is linked to the ester bond, thereby resulting in a change in the chemical shift of H connected with C12. As the chemical shift of H in methyl at 0.87 ppm does not change before and after the reaction, it is used

• reaction mechanism with catalyst [HSO3-BDBU]H2PO4 is depicted in Scheme 3. Firstly, the Brønsted acidic IL [HSO3-BDBU]H2PO4 activates the carbonyl group of ricinoleic acid, leading to the generation of intermediate A. Concurrently, the hydroxy group in another ricinoleic acid molecule may be activated by

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

• )), two aromatic methine protons (δH 6.64 (1H, br s, H-2) and 6.72 (1H, br s, H-4)), and a hydrogen-bonded hydroxy group (δH 11.82 (1H, br s, 4-OH)). The 13C NMR (Table 1) and DEPT data showed 16 carbon signals comprising two sp3 methyl groups (δC 22.5, 54.0), two sp3 methylene units (δC 28.0, 34.4), two

• benzene ring with a methyl group at its C-3 position. The hydrogen-bonded hydroxy group was attached to the C-1 position, as evidenced by HMBC correlations from 4-OH to C-1 (δC 160.3), C-2 (δC 112.7), and C-4a (δC 155.9), which also implied that C-9a was hydrogen-bonded to a carbonyl group. Furthermore

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• reduced gauche interactions [55]. Subsequent epoxidation at the double bond directed by the hydroxy group and using m-chloroperbenzoic acid allowed to install two additional stereocenters with complete control of the relative stereochemistry in 68% yield. Such two-step synthesis proved to proceed also in

Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: experimental and computational evidence for intramolecular and intermolecular C–F···H–C bonds

• Vuyisa Mzozoyana,
• Fanie R. van Heerden and
• Craig Grimmer

Beilstein J. Org. Chem. 2020, 16, 190–199, doi:10.3762/bjoc.16.22

• hydroxy group of coumarin 5 with dimethyl sulfate, to form 4-(2-fluorophenyl)-7-methoxycoumarin (6). Discussion During the synthesis of coumarin 6, solution-state NMR spectroscopy was used to characterize compounds 3, 5, and 6 (1H and 13C spectra are available in Supporting Information File 1). The 1H

• methoxy group while 5 has a hydroxy group, a similar study was carried out for coumarin 5 (Figure S10b, Supporting Information File 1). The question posed at this point was “is this a through-bond (TB) or through-space (TS) effect”? To answer this question, we analysed a 13C-{1H} spectrum of coumarin 6

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• unit of indanocine (which is attached in ortho-position to the key south ring methoxy group) by a hydroxy function, giving HITub-1 (Figure 2). When HITub-1 later proved less bioactive than we had wished, we explored steric and polarity changes to this south ring hydroxy group by methylation (HITub-2

• deprotonation of the hydroxy group, and that the lack of observable photoswitchability arose due to fast free rotation around the C–C single bond connecting the thioindigo and hemistilbene motifs. Interestingly, in neutral or acidic aqueous media where the quinoidal structure is not present (λmax ca. 370, 480

• (in ortho-position to the key south ring methoxy group) has been replaced by a synthetically more accessible hydroxy group (delivered via demethylation of a trimethoxy precursor through BBr3). The hydroxy and amino groups have similar size and polarity, and can both act as H-bond donors or acceptors

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• being hydroxy group removal followed by intramolecular formation of a sulfur–carbon bond. The second step seemed to be slow, and the intermediate carbocation could be trapped in the form of an alkenylphosphine sulfide. The comparison of the reactivity of the same substrate under two different reaction

The interaction between cucurbit[8]uril and baicalein and the effect on baicalein properties

• Xiaodong Zhang,
• Jun Xie,
• Zhiling Xu,
• Zhu Tao and
• Qianjun Zhang

Beilstein J. Org. Chem. 2020, 16, 71–77, doi:10.3762/bjoc.16.9

• [8] fare forming hydrogen bonds, the cycle B and and a part of cycle C of baicalin inserted into the cavity of the Q[8]. This may be attributed to chrysin containing one hydroxy group less than baicalein, which reduced the hydrophilicity of cycle A, making it enter into the hydrophobic cavity of Q[8

• ] easily. Because the hydroxy group on the carboxylic acid of the baicalin formed a hydrogen bond with the oxygen atoms of Q[8] at the portal, cycle C of baicalin was pushed into the cavity of Q[8]. Therefore, the inclusion model of cucurbit[8] with flavonoid compounds was determined by the structure of

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

• orientation of the anomeric hydroxy group was proven by NOESY correlations between the H-2 proton and both geminal protons of the CH2P unit. A strong NOE was also observed for the upfield-shifted doublet of doublets at 1.71 ppm of the methylene group, which had an additional NOE correlation with the broad

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• with more than one free hydroxy group allows reducing the usage of protecting groups, and thus developing simpler reaction sequences for the synthesis of oligosaccharides and glycoconjugates. A current alternative is the use of biocatalysts [4][5], although limited specific enzymes are available

• , whose relative reactivity is still rather poorly understood [6]. Regioselective approaches for the glycosylation of acceptors with more than one free hydroxy group have been developed, and in some of the cases they were successfully rationalized [7][8][9]. In other cases, the results could not be