Bifunctional thiourea-catalyzed asymmetric [3 + 2] annulation reactions of 2-isothiocyanato-1-indanones with barbiturate-based olefins

• Jiang-Song Zhai and
• Da-Ming Du

Beilstein J. Org. Chem. 2022, 18, 25–36, doi:10.3762/bjoc.18.3

• solubility of this substrate. The absolute configuration of the chiral product 3ae was unambiguously identified on the basis of single-crystal X-ray diffraction analysis as (2S,3'S) (Figure 4) [33]. The configurations of the other products were assigned by analogy to 3ae. In order to further prove the

The enzyme mechanism of patchoulol synthase

• Houchao Xu,
• Bernd Goldfuss,
• Gregor Schnakenburg and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2022, 18, 13–24, doi:10.3762/bjoc.18.2

• no. 1491695) [17], but these data did not allow to conclude on the absolute configuration of compound 3. We now obtained 3 as a crystalline material and performed an X-ray structural analysis through anomalous dispersion using Cu Kα irradiation (Table S2 in Supporting Information File 1), resulting

• in the structure of 3 with the absolute configuration as shown in Figure 2. The absolute configuration of 3 was furthermore independently confirmed through a stereoselective deuteration strategy (Scheme 4; all labelling experiments of this study are summarised in Supporting Information File 1, Table

• deuterated carbons. The NOESY-based assignment of the diastereotopic hydrogens at these carbons for the unlabelled compound then allows to conclude on the absolute configuration of alcohol 3. A second set of experiments made use of (R)- and (S)-(1-13C,1-2H)IPP [20] that were enzymatically converted with

Unsaturated fatty acids and a prenylated tryptophan derivative from a rare actinomycete of the genus Couchioplanes

• Shun Saito,
• Kanji Indo,
• Naoya Oku,
• Hisayuki Komaki,
• Masashi Kawasaki and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2939–2949, doi:10.3762/bjoc.17.203

• hydroxylation on the same carbon. This was supported by COSY correlations establishing the connectivity from H-5 to H-8, and completely the same HMBC and NOESY correlations for the remaining part to those observed for 1 and 2 (Figure 2). To address the absolute configuration, 4 was esterified with TMS

• -7 to C-1' and from H-1' to C-6. The absolute configuration was determined by chiral anisotropy analysis after derivatization with each of the phenylglycine methyl ester (PGME) enantiomers [27], which gave positive ΔδH(S-R) values for NH-1, H-2, H-4, H-5 and H-8 and negative values for H-9, NH-11 and

Solvent-free synthesis of enantioenriched β-silyl nitroalkanes under organocatalytic conditions

• Akhil K. Dubey and
• Raghunath Chowdhury

Beilstein J. Org. Chem. 2021, 17, 2642–2649, doi:10.3762/bjoc.17.177

• dictated by the absolute configuration of the products. To our delight, catalyst VIII, the pseudoenantiomeric catalyst of VII, allowed to synthesize the enantiomeric products ent-3 (Scheme 3) in high yields and enantioselectivities comparable to the corresponding enantiomers 3 under the optimized reaction

Targeting active site residues and structural anchoring positions in terpene synthases

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 2441–2449, doi:10.3762/bjoc.17.161

• . Table S3 and Figure S8. Determination of the absolute configuration of compounds 8 and 9. Partial HSQC spectra of A) unlabelled 8, B) unlabelled 9, C) the mixture of labelled 8 and 9 obtained from (R)-(1-13C,1-2H)GGPP, and D) the mixture of labelled 8 and 9 obtained from (S)-(1-13C,1-2H)GGPP. The colour

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

• Martin Kamlar,
• Robert Reiberger,
• Martin Nigríni,
• Ivana Císařová and
• Jan Veselý

Beilstein J. Org. Chem. 2021, 17, 2433–2440, doi:10.3762/bjoc.17.160

• time. To determine the absolute configuration of aminals 3a–t, derivative 3l was subjected to X-ray crystallographic analysis. The absolute configuration of the stereogenic center (C1) was assigned as R (Figure 2, for details see Supporting Information File 1) [36], which is in agreement with the

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• compounds, 1–6, were given the trivial names of brevipolides A–F, respectively, and the absolute configuration was determined by analysis of data obtained from their CD spectra and by Mosher’s ester formation, as C6R, C1’S, C2’S, and C4’S. The C6’ stereocenter at that time could not be established due to a

• comprehensive combination of quantum mechanical calculations and experimental spectroscopic analysis of their NMR and ECD data, to have a unique tetrahydrofuran ring instead of the cyclopropane functionality. The absolute configuration of these five compounds were evaluated and all conserved as C6R, C1’S, C2’R

Isolation and characterization of new phenolic siderophores with antimicrobial properties from Pseudomonas sp. UIAU-6B

• Emmanuel T. Oluwabusola,
• Olusoji O. Adebisi,
• Fernando Reyes,
• Kojo S. Acquah,
• Mercedes De La Cruz,
• Larry L. Mweetwa,
• Joy E. Rajakulendran,
• Digby F. Warner,
• Deng Hai,
• Rainer Ebel and
• Marcel Jaspars

Beilstein J. Org. Chem. 2021, 17, 2390–2398, doi:10.3762/bjoc.17.156

• analyses. The absolute configuration of the threonine residue in compounds 1–5 was determined by Marfey analysis. The antimicrobial evaluation of compound 4 exhibited the most potent activity against vancomycin-sensitive Enterococcus faecium VS144754, followed by 3 and 5, with MIC values ranging from 8 to

• carboxamide C-10 (δC 172.9) and the quaternary carbon C-16 (δC 140.2), between H2-15 and H-18/20 to the quaternary carbon C-16, and a strong correlation from H-15 and H-19 to C-17/20 (δC 129.9). The new oxazoline derivative 5 was named pseudomonbactin B. The absolute configuration of the threonine residue in

Phenolic constituents from twigs of Aleurites fordii and their biological activities

• Kyoung Jin Park,
• Won Se Suh,
• Da Hye Yoon,
• Chung Sub Kim,
• Sun Yeou Kim and
• Kang Ro Lee

Beilstein J. Org. Chem. 2021, 17, 2329–2339, doi:10.3762/bjoc.17.151

• [15]. The relative configuration at C-7/C-8 of 1 was established as trans through the relatively small coupling constant (6.1 Hz) [10][16]. The analysis of the ECD spectrum of 1 determined the absolute configuration of 1 to be 7S and 8R (positive Cotton effects (CEs) at 292 and 248 nm, and a negative

• spectrum of 2 showed negative CEs at 276 nm and 229 nm and a positive CE at 248 nm, indicating the absolute configuration of C-7 and C-8 as R (Figure S15 in Supporting Information File 1) [19]. Therefore, the structure of compound 2 was determined to be (7R,8R)-dihydrodehydrodiconiferyl alcohol 4-O-α-ʟ

• absolute configuration. The planar structure of 3 was further confirmed by analysis of 2D NMR data, including COSY, HSQC, and HMBC (Figure 2). The determination of the stereochemistry for the sugar unit of 3 was conducted following the same method as for compound 2. The structure of the aglycone 3a

Nomimicins B–D, new tetronate-class polyketides from a marine-derived actinomycete of the genus Actinomadura

• Zhiwei Zhang,
• Tao Zhou,
• Taehui Yang,
• Keisuke Fukaya,
• Enjuro Harunari,
• Shun Saito,
• Katsuhisa Yamada,
• Chiaki Imada,
• Daisuke Urabe and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2194–2202, doi:10.3762/bjoc.17.141

• absolute configuration was determined by combination of NOESY/ROESY and ECD analyses. Nomimicins B, C, and D showed antimicrobial activity against Gram-positive bacteria, Kocuria rhizophila and Bacillus subtilis, with MIC values in the range of 6.5 to 12.5 μg/mL. Nomimicins B and C also displayed

• (Table S1, Supporting Information File 1) and 3JHH coupling constants [15]. The absolute configuration of 1 was deduced to be the same as 4 in consideration of the overall similarity of the electronic circular dichroism (ECD) spectra of 1 and 4 (Figure 4). This proposition was evidenced by the density

• functional theory (DFT) calculation of the ECD spectrum for 4, for which the absolute configuration was established by the modified Mosher’s method in our previous work [15]. Since the acyltetronic acid exists as a mixture of keto–enol tautomers, the calculation was carried out using the four possible

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• substitution reaction between the coumarin and the activated MBH substrate, it is possible to obtain functionalized coumarins 41 (Scheme 13). Furthermore, the absolute configuration of the stereogenic center was determined by X-ray crystallography. The enantioselective synthesis of cyclopropa[c]coumarins 45

• half-thioesters 67 to coumarins 66 using a sulphonamide organocatalyst 69 was reported by Nakamura et al. [55]. The hydrogen bond between the secondary amine and the coumarin carboxyl provides a nucleophilic addition on the Re face, and therefore resulting in products 68 with R absolute configuration

• with high ee in the two first cycles, although the yield of the product in the first cycle was lower (Scheme 28b). Finally, the absolute configuration of the products was determined by ECD analysis. Zheng et al. described an asymmetric organocatalyzed domino reaction between 4-hydroxycoumarins 1 and

Total synthesis of ent-pavettamine

• Memory Zimuwandeyi,
• Manuel A. Fernandes,
• Amanda L. Rousseau and
• Moira L. Bode

Beilstein J. Org. Chem. 2021, 17, 1440–1446, doi:10.3762/bjoc.17.99

• 1995, was previously identified as a polyamine with C2 symmetry and a 1,3-syn-diol moiety on a C10 carbon backbone – one of very few substituted polyamines to be isolated from nature. Its absolute configuration was later established by our first reported total synthesis in 2010. Herein we report the

Analogs of the carotane antibiotic fulvoferruginin from submerged cultures of a Thai Marasmius sp.

• Birthe Sandargo,
• Leon Kaysan,
• Rémy B. Teponno,
• Christian Richter,
• Benjarong Thongbai,
• Frank Surup and
• Marc Stadler

Beilstein J. Org. Chem. 2021, 17, 1385–1391, doi:10.3762/bjoc.17.97

• of potential pharmaceutical interest. Klein et al. obtained a crystal structure of fulvoferruginin (1) [8], as did Huneck et al. for hercynolactone [9], verifying their relative configuration. Huo et al. have further confirmed the absolute configuration of compound 1 by utilizing the CD exciton

• biosynthetic genes as the parent compound, and postulate that the congeners should also have the same absolute configuration as compound 1 [10]. For a long time, fulvoferruginin was only known to be produced by a strain of M. fulvoferrugineus found in Northern America, but there is a recent report on the

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• diastereoselectivities were observed with less bulky methyl 2-bromo-2-butenoate (R2 = CH3CH=), leading to an almost complete loss of cis/trans selectivity by the reaction with aliphatic aldimines 14. The absolute configuration of the reaction products was unambiguously determined after X-ray crystallographic analysis of

• reaction of N-tert-butanesulfinyl trifluoromethyl ketimines (SS)-37 with dimethylsulfoxonium methylide 38 gave trifluoromethylated aziridines 39 in moderate to excellent yields (45–93%), and good diastereoselectivities (86:14 to >99:1 dr). The absolute configuration of compounds 39 was determined by X-ray

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

• Ákos Bajtel,
• Mounir Raji,
• Matti Haukka,
• Ferenc Fülöp and
• Zsolt Szakonyi

Beilstein J. Org. Chem. 2021, 17, 983–990, doi:10.3762/bjoc.17.80

• 9 ring system (Scheme 1). The absolute configuration of compound 9 was determined by 2D NMR spectroscopic techniques. Clear NOE signals were observed between the H-7a and Me-10 as well as the Ha-9 and Me-10 protons. Beside NOESY experiments, the structure was also elucidated by X-ray crystallography

• configuration depicted in Scheme 2. Beside 2D NMR spectroscopic studies, the absolute configuration of compound 12 was determined by its transformation into the corresponding aminodiols 13 and 14, comparing the products with those obtained from the regioisomer 9 (discussed in Scheme 3). Synthesis and

The synthesis of chiral β-naphthyl-β-sulfanyl ketones via enantioselective sulfa-Michael reaction in the presence of a bifunctional cinchona/sulfonamide organocatalyst

• Deniz Tözendemir and
• Cihangir Tanyeli

Beilstein J. Org. Chem. 2021, 17, 494–503, doi:10.3762/bjoc.17.43

• product was ultimately obtained at room temperature (83% ee, Table 2, entry 3). The absolute configuration of the product was assigned as “S” by comparing the obtained optical rotation value with the values in the literature for the organocatalytic SMA of thiols to trans-chalcone derivatives [29][42]. A

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

Synthesis of legonmycins A and B, C(7a)-hydroxylated bacterial pyrrolizidines

• Wilfred J. M. Lewis,
• David M. Shaw and
• Jeremy Robertson

Beilstein J. Org. Chem. 2021, 17, 334–342, doi:10.3762/bjoc.17.31

• ) the jenamidines A–C, from another Streptomyces sp. strain [12], although these molecules were not recognized as pyrrolizidines until Snider’s subsequent synthetic work revised the structural assignment [13][14] and, separately, established the absolute configuration of natural (+)-NP25302 [15

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• value reported by the group of R. J. K. Taylor. Therefore, the absolute configuration assignment of (3R)-inthomycin C ((–)-3) as described by the Ryu and Hatakeyama groups contradicted with that of the R. J. K. Taylor group. Later, the groups of Hale and Hatakeyama tried hard to eliminate all the

Chemical constituents of Chaenomeles sinensis twigs and their biological activity

• Joon Min Cha,
• Dong Hyun Kim,
• Lalita Subedi,
• Zahra Khan,
• Sang Un Choi,
• Sun Yeou Kim and
• Chung Sub Kim

Beilstein J. Org. Chem. 2020, 16, 3078–3085, doi:10.3762/bjoc.16.257

• Supporting Information File 1). The strong NOESY cross-peaks of H-2 with H-6 and H-11 and H-6 with H-11 indicated that these three protons are co-facial (Figure 2B and Supporting Information File 1). The absolute configuration of C-6 was assigned as S by a well-established ECD empirical rule [22]. In brief

• and the analysis of the ΔδS-R values of all protons in 1a indicated a 2S and 9R configuration (Figure 2D). Finally, the absolute configuration of the glucopyranose was assigned as ᴅ by comparing the retention time of its chiral derivative with those of authentic samples [16][26]. Therefore, the

• , a systemic analysis of the ECD data of 13 with its diastereomers and simple derivatives showed that a positive or negative Cotton effect around 240–245 nm is indicative of the 6R or 6S configuration, respectively. From a positive Cotton effect at 245 nm of compound 1 (Figure 2C, left), the absolute

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

• Florian Mann,
• Daiane Szczerbowski,
• Lisa de Silva,
• Melanie McClure,
• Marianne Elias and
• Stefan Schulz

Beilstein J. Org. Chem. 2020, 16, 2776–2787, doi:10.3762/bjoc.16.228

• , microderivatizations, and synthesis of representative compounds. The absolute configuration of 12 was determined to be R. The two subspecies differed not only in the composition of the ester bouquet, but also in the composition of more volatile androconial constituents. While some individuals of I. s. aquinia

• -enoate (12) was performed to verify the structural proposal and to determine the absolute configuration of the natural product (Scheme 4). The commercially available epoxide (S)-22 served as chiral starting material. 1,9-Nonanediol (19) was monobrominated and oxidized with IBX to yield 9-bromononanal (20

• eluting ester is isoprenyl (Z)-3-acetoxy-13-octadecenoate, while the earlier eluting one is the 11-isomer. With optically active material in hand, the absolute configuration of 12 was determined by enantioselective gas chromatography. Because direct separation of the large esters seemed to be difficult

Nocarimidazoles C and D, antimicrobial alkanoylimidazoles from a coral-derived actinomycete Kocuria sp.: application of ¹J_C,H coupling constants for the unequivocal determination of substituted imidazoles and stereochemical diversity of anteisoalkyl chains in microbial metabolites

• Md. Rokon Ul Karim,
• Enjuro Harunari,
• Amit Raj Sharma,
• Naoya Oku,
• Kazuaki Akasaka,
• Daisuke Urabe,
• Mada Triandala Sibero and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 2719–2727, doi:10.3762/bjoc.16.222

• (Figure S31, Supporting Information File 1). Thus, the amino substitution at C-5 in 1 was unequivocally established (Figure 3). The absolute configuration at C-11 in the anteisoalkanoyl chain was determined by the Ohrui–Akasaka method [29]. The imidazole ring was degraded by oxidation using ruthenium

• (chromatographically equivalent to (R)-10-(R)-2A1P) and 184 min for (S)-10-(R)-2A1P, and nat-10-(R)-2A1P gave both peaks with the area ratio of 72.9:27.1 (Figure 4a). Therefore, 1 was confirmed as an enantiomeric mixture comprising 73% of the R- and 27% of the S-enantiomer. We also analyzed the absolute configuration

• of nocarimidazole B (4) produced by strain TK35-5. The same compound was originally isolated from marine Nocadiopsis, but the absolute configuration was not elucidated. The conversion of 4 into the derivative nat-11-(R)-2A1P, followed by HPLC analysis, revealed that 4 is an enantiomerically pure S

Asymmetric Mannich reactions of (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimines with yne nucleophiles

• Ziyi Li,
• Li Wang,
• Yunqi Huang,
• Haibo Mei,
• Hiroyuki Konno,
• Hiroki Moriwaki,
• Vadim A. Soloshonok and
• Jianlin Han

Beilstein J. Org. Chem. 2020, 16, 2671–2678, doi:10.3762/bjoc.16.217

• synthesis of chiral α-trifluoromethylated propargylamines. In order to determine the absolute configuration of the chiral addition products, we successfully performed a crystallographic analysis of the minor product 3a. The structure is shown in Figure 2, the absolute configuration of the newly generated

Computational tools for drawing, building and displaying carbohydrates: a visual guide

• Kanhaya Lal,
• Rafael Bermeo and
• Serge Perez

Beilstein J. Org. Chem. 2020, 16, 2448–2468, doi:10.3762/bjoc.16.199

• of completion, the full description of a monosaccharide should obey the following rules: absolute configuration>[]. It is thus necessary to include such information

Muyocopronones A and B: azaphilones from the endophytic fungus Muyocopron laterale

• Ken-ichi Nakashima,
• Junko Tomida,
• Tomoe Tsuboi,
• Yoshiaki Kawamura and
• Makoto Inoue

Beilstein J. Org. Chem. 2020, 16, 2100–2107, doi:10.3762/bjoc.16.177

• ′/H-3′ (J = 8.2 Hz) and H-3′/H-4′ (J = 3.2 Hz). To establish the absolute configuration of the side chain, we therefore employed the modified Mosher’s method [21]. Although we initially attempted the preparation of the α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) esters using 1.2 equivalents of

• shifts between 1a and 1b (Δδ(S)-MTPA−(R)-MTPA), the absolute configuration of the side chain was established to be the (2′R,3′R,4′S) configuration (Scheme 1B). The absolute configuration at the C-7 position of the azaphilones can be established by the positive and negative Cotton effects at the longest

• wavelength around 360 nm corresponding to 7S and 7R [22][23][24]. Therefore, positive Cotton effects at 325 and 355 nm in the electronic circular dichroism (ECD) spectrum of 1 indicated that the absolute configuration of the C-7 position was S (Figure 3). Furthermore, the coupling constant between H-10/H-11