New azodyrecins identified by a genome mining-directed reactivity-based screening

• Atina Rizkiya Choirunnisa,
• Kuga Arima,
• Yo Abe,
• Noritaka Kagaya,
• Kei Kudo,
• Hikaru Suenaga,
• Junko Hashimoto,
• Manabu Fujie,
• Noriyuki Satoh,
• Kazuo Shin-ya,
• Kenichi Matsuda and
• Toshiyuki Wakimoto

Beilstein J. Org. Chem. 2022, 18, 1017–1025, doi:10.3762/bjoc.18.102

• N2H4, which could be generated upon the acid hydrolysis of azoxy natural products. In the assay, N2H4 is captured by two equivalents of p-dimethylaminobenzaldehyde (DAB) to generate p-dimethylaminobenzaldazine, which can be sensitively detected by HPLC by monitoring the UV absorption at 485 nm (Scheme

• Streptomyces sp. RM72 were first partitioned by water and ethyl acetate, and then the organic layer was further fractionated by silica gel column chromatography. Fractionation by reversed-phase HPLC yielded ten compounds (1–10) that generate N2H4 upon acid hydrolysis. The combination of 1H and 13C NMR with a

Isolation and biosynthesis of daturamycins from Streptomyces sp. KIB-H1544

• Yin Chen,
• Jinqiu Ren,
• Ruimin Yang,
• Jie Li,
• Sheng-Xiong Huang and
• Yijun Yan

Beilstein J. Org. Chem. 2022, 18, 1009–1016, doi:10.3762/bjoc.18.101

• gel (75–150 µm, Mitsubishi Chemical Corporation, Tokyo, Japan). Semipreparative HPLC was conducted on a HITACHI Chromaster system equipped with a DAD detector, a YMC-Triart C18 column (250 × 10 mm, i.d. 5 μm), and a flow rate of 3.0 mL/min. LC–MS was performed using an Agilent 1200 series HPLC system

• , the extract was purified by silica gel chromatography and semipreparative HPLC to yield daturamycin A (1) (4.5 mg), daturamycin B (2) (1.8 mg), daturamycin C (3) (8.7 mg), terferol (4) (2.4 mg), BTH-II0204-207: D (5) (2.1 mg), betulinan A (6) (6.2 mg). Identification of new compounds Daturamycin A (1

• . The supernatant was analyzed by HPLC. Structures of compounds 1–6, atromentin, and echoside C. (A) Key 2D NMR correlations of compounds 1 and 2. (B) X-ray crystal structure of compounds 1 and 3. (A) The biosynthetic gene cluster of daturamycins. (B) Proposed biosynthetic pathway of daturamycins. (A

Anti-inflammatory aromadendrane- and cadinane-type sesquiterpenoids from the South China Sea sponge Acanthella cavernosa

• Shou-Mao Shen,
• Qing Yang,
• Yi Zang,
• Jia Li,
• Xueting Liu and
• Yue-Wei Guo

Beilstein J. Org. Chem. 2022, 18, 916–925, doi:10.3762/bjoc.18.91

• enantiomers [(+)-4/(−)-4 and (+)-5/(−)-5], respectively, by using chiral-phase HPLC. The structures of new compounds were elucidated by extensive spectroscopic analysis and comparison with the reported data. In addition, the absolute configuration of optically pure (+)-1 and 2 were determined by time

• difference between them was obvious at C-10 and its neighboring carbons (e.g., C-1 and C-14). Considering the insignificant distinction between these chemical shift values (∆δ ≤ 2.4), compounds 4 and 5 were further analyzed using the same RP-HPLC conditions to examine whether they were the same compound (see

• determine the stereochemistry at C-7 and C-10 of compounds 4 and 5. Since both 4 and 5, as mentioned above, are respective racemic mixtures, chiral-phase HPLC was then applied to separate each of them (see Figures S2 and S5 in Supporting Information File 1). As expected, new (+)-maninsigin D [(+)-4, 0.8 mg

Efficient production of clerodane and ent-kaurane diterpenes through truncated artificial pathways in Escherichia coli

• Fang-Ru Li,
• Xiaoxu Lin,
• Qian Yang,
• Ning-Hua Tan and
• Liao-Bin Dong

Beilstein J. Org. Chem. 2022, 18, 881–888, doi:10.3762/bjoc.18.89

• produced new peaks in the HPLC profiles after a 3-day fermentation. Larger scale (3 L) fermentations of DL10004 and DL10006 led to the isolation of 45 mg and 90 mg of terpentetriene and ent-kaurene, respectively, whose 1H and 13C NMR spectra supported their chemical structures (Figures S4–S7 in Supporting

First series of N-alkylamino peptoid homooligomers: solution phase synthesis and conformational investigation

• Maxime Pypec,
• Laurent Jouffret,
• Claude Taillefumier and
• Olivier Roy

Beilstein J. Org. Chem. 2022, 18, 845–854, doi:10.3762/bjoc.18.85

• Information Supporting Information File 67: Experimental procedures, HPLC analytical data, NMR spectra and variable concentration study, infrared spectra, full X-ray data for 2, computation data, and additional TEM images for compound 2. Supporting Information File 68: Crystallographic information file (CIF

The stereochemical course of 2-methylisoborneol biosynthesis

• Binbin Gu,
• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2022, 18, 818–824, doi:10.3762/bjoc.18.82

• Sharpless epoxidation as a key step and purification of enantiomerically enriched intermediates through HPLC separation on a chiral stationary phase. Their enzymatic conversion with 2-methylisoborneol synthase (2MIBS) demonstrates that (R)-2-Me-LPP is the on-pathway intermediate, while a minor formation of

• decide, if only one enantiomer of LPP serves as the precursor to 1. Purification of the enantiomers of 2-Me-LPP In order to obtain the enantiomers of 2-Me-LPP with high purity, the synthetically obtained enantiomerically enriched compounds 6a and 6b were purified by HPLC using a chiral stationary phase

• comparison in these analyses. Conclusion Both enantiomers of 2-Me-LPP can be selectively prepared using a Sharpless epoxidation strategy in high enantiomeric purity of >75% ee. HPLC purification of the synthetic precursor 2-methyllinalool using a chiral stationary phase can make the pure enantiomers

Continuous flow synthesis of azobenzenes via Baeyer–Mills reaction

• Jan H. Griwatz,
• Anne Kunz and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2022, 18, 781–787, doi:10.3762/bjoc.18.78

• acetonitrile, and subsequently examined by HPLC analysis (for details, see Supporting Information File 1). At lower temperature, AB (1a) could be detected, but only a low conversion of the starting materials was observed (Figure 2). At higher temperature, the product/starting material ratio was improved but

• residence time can be individually varied (Figure 2). Optimization of the Baeyer–Mills reaction of nitrosobenzene (3) with aniline (2a) to AB (1a). The numbers in the figure result from the ratio of the integral of the HPLC peak of AB (1a) to the integral of AB (1a), nitrosobenzene (3), and aniline (2a) at

Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• biphasic mixture is separated using a membrane reactor with a PTFE membrane. While the aqueous layer is directly quenched with an aqueous solution of sodium sulfite, the organic layer containing triperoxide 55 in dodecane is collected in a flask and directly pumped using an HPLC pump in an inductively

Identification of the new prenyltransferase Ubi-297 from marine bacteria and elucidation of its substrate specificity

• Jamshid Amiri Moghaddam,
• Huijuan Guo,
• Karsten Willing,
• Thomas Wichard and
• Christine Beemelmanns

Beilstein J. Org. Chem. 2022, 18, 722–731, doi:10.3762/bjoc.18.72

• appropriate fraction was collected, evaporated, and purified by preparative HPLC (Shimadzu) over a phenyl-hexyl column (Luna, 5 µm, 250 × 21.2 mm, 100 Å) (eluent: H2O/MeCN + 0.1% formic acid 80:20 to 50:50). The appropriate fraction was collected and evaporated to afford farnesylated 8-HQA. HRMS/MS analysis

Shift of the reaction equilibrium at high pressure in the continuous synthesis of neuraminic acid

• Jannis A. Reich,
• Miriam Aßmann,
• Kristin Hölting,
• Paul Bubenheim,
• Jürgen Kuballa and
• Andreas Liese

Beilstein J. Org. Chem. 2022, 18, 567–579, doi:10.3762/bjoc.18.59

• -continuously already exist in the food industry, continuous reactors containing a high-performance liquid chromatography (HPLC) pump and a fixed-bed reactor at high pressure are still a relatively new concept. The use of a back pressure regulator up to 10 MPa (100 bar) was already demonstrated by Ötvös et al

• initial activity was analyzed using a standard activity assay. High-performance liquid chromatography (HPLC) For quantification of the product N-acetylneuraminic acid, an Agilent HPLC system connected with a variable wavelength detector at 210 nm was used. Separation was realized with a Nucleogel Sugar

• mM ManNAc, 2 mM NAD, and 0.05 mL ManDH solution with 3 kU/mL. After starting the reaction, the mixture was incubated at room temperature for 30 minutes. The resulting NADH concentration was measured with an Eppendorf spectrophotometer at 340 nm. High-pressure set-up An HPLC pump (Nexera X2 LC-30AD

Terpenoids from Glechoma hederacea var. longituba and their biological activities

• Dong Hyun Kim,
• Song Lim Ham,
• Zahra Khan,
• Sun Yeou Kim,
• Sang Un Choi,
• Chung Sub Kim and
• Kang Ro Lee

Beilstein J. Org. Chem. 2022, 18, 555–566, doi:10.3762/bjoc.18.58

• spectrometer at 700 MHz (1H) and 175 MHz (13C) with solvent resonance as the internal standard (1H NMR: CD3OD at 3.31 ppm; 13C NMR: CD3OD at 49.00 ppm). To practice LC–MS analysis, an Agilent 1200 Series high-performance liquid chromatography (HPLC) system furnished with a diode array detector and a 6130

• Series ESIMS spectrometer connected to an analytical Kinetex C18 column (250 mm × 4.6 mm, 5 µm; Phenomenex, Torrance, CA, USA) was utilized. The Agilent 7820A GC system equipped with a 5977B mass selective detector system was controlled by qualitative navigator version B.08.00 software. Preparative HPLC

• to a silica gel column (CHCl3/MeOH, 20:1 → 1:1) to give five fractions (C1–C5). Fraction C2 (3.0 g) was applied to an RP-C18 silica gel column (50% MeOH) to give 12 subfractions (C2a–C2l). Compound 6 (4 mg, tR = 25.9 min) was yielded by purifying subfraction C2h (32 mg) using a semipreparative HPLC

Tosylhydrazine-promoted self-conjugate reduction–Michael/aldol reaction of 3-phenacylideneoxindoles towards dispirocyclopentanebisoxindole derivatives

• Sayan Pramanik and
• Chhanda Mukhopadhyay

Beilstein J. Org. Chem. 2022, 18, 469–478, doi:10.3762/bjoc.18.49

• formed by multistep reaction progression where, to overcome severe steric hindrance, two oxindole moieties are in trans orientation. HPLC data of compound 3o ensures >95:5 dr (Supporting Information File 1). The structure was further confirmed by NOESY spectra of compounds 3e (Figure 3) and 3j

• (multiplet). HRMS with an ESI resource were acquired using a Waters XEVO-G2S Q TOF mass spectrometer. HPLC were recorded using an Agilent 1200 Series auto sampler HPLC system. Melting points were recorded with an open capillary on an electrical melting point apparatus and the single crystal structure of the

The asymmetric Henry reaction as synthetic tool for the preparation of the drugs linezolid and rivaroxaban

• Martin Vrbický,
• Karel Macek,
• Jaroslav Pochobradský,
• Jan Svoboda,
• Miloš Sedlák and
• Pavel Drabina

Beilstein J. Org. Chem. 2022, 18, 438–445, doi:10.3762/bjoc.18.46

• de were observed and the presence of the major S-enantiomer in the products 1 and 2 was confirmed by chiral HPLC analysis. Moreover, an enhancement of the abundance of the major epimer in the nitroaldols 22, 24, and 26 as well as the amides 27 and 28 was examined. Generally, epimers represent pairs

• HPLC chromatograms.

Four bioactive new steroids from the soft coral Lobophytum pauciflorum collected in South China Sea

• Di Zhang,
• Zhe Wang,
• Xiao Han,
• Xiao-Lei Li,
• Zhong-Yu Lu,
• Bei-Bei Dou,
• Wen-Ze Zhang,
• Xu-Li Tang,
• Ping-Lin Li and
• Guo-Qiang Li

Beilstein J. Org. Chem. 2022, 18, 374–380, doi:10.3762/bjoc.18.42

• J-815 CD spectropolarimeter. Optical rotations were measured with a Jasco P-1020 polarimeter. Semi-preparative HPLC (Agilent Technologies 1260 Infinity II) equipped with a reversed-phase column ((YMC-packed C18, 5 µm, 250 × 10 mm, 2.0 mL/min) was used to purify samples. Silica gel (300–400 mesh

• subfractions (F41–F43). Subfraction F41 (2.1 g) was chromatographed over silica gel column (PE/acetone, 50:1 to 2:1) to give seven subfractions (F411–F417), F411 (330 mg) was purified by semi-preparative HPLC (ODS, 5 µm, 250 × 10 mm; methanol/water, 95:5, v/v; 2.0 mL/min) to afford compound 4 (2.3 mg), 5 (4.7

• mg), 6 (15.5 mg) and 7 (10.2 mg). Fr.412 (210 mg) was chromatographed on semi-preparative HPLC (ODS, 5 µm, 250 × 10 mm; methanol/water, 85:15, v/v; 2.0 mL/min) to give compound 1 (2.5 mg), 2 (5.8 mg) and 3 (13.3 mg). Identification of new compounds Compound 1: colorless crystals; [α]D25 −19.28 (c

Amamistatins isolated from Nocardia altamirensis

• Till Steinmetz,
• Wolf Hiller and
• Markus Nett

Beilstein J. Org. Chem. 2022, 18, 360–367, doi:10.3762/bjoc.18.40

• as eluent. Fractions that showed a color change in the CAS assay were pooled and subjected to semipreparative reversed-phase HPLC. This led to the isolation of six CAS active compounds (1–6; Figure 1). The major metabolite 1 (12 mg) was obtained as a slight reddish oil. High resolution (HR) ESIMS

• over Polygoprep 60-50 C18 (Macherey-Nagel) using an increasing concentration of methanol in water. Fractions that gave a color change in the CAS assay were prepurified by reversed-phase HPLC using a Nucleodur C18 ec column (125 × 21 mm, 5 μm, Macherey-Nagel) and a gradient of methanol in water

Synthesis of piperidine and pyrrolidine derivatives by electroreductive cyclization of imine with terminal dihaloalkanes in a flow microreactor

• Yuki Naito,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 350–359, doi:10.3762/bjoc.18.39

• s. The yield of 3a was determined by HPLC. After mixing the five fraction samples, we attempted to isolate 3a from the mixture, and obtained 78.4 mg (55% isolated yield) of 3a (entry 1 of Table 9). The desired piperidine derivative could be obtained on a scale of several tens of milligrams in

• introduced to the microreactor by a syringe pump (KDS100, KdScientific Muromachi Kikai) during the electrosynthesis. Electroreductive cyclization was conducted using a potentiogalvanostat (HABF-501A, Hokuto Denko). High-performance liquid chromatography (HPLC) analysis for 3a and 4 was performed with a

• with the terminal dihaloalkane to produce the corresponding heterocyclic compounds. The THF solvent is oxidized at the anode to generate protons. After electrolysis, 1 mL of the reaction solution was collected from the outlet of the reactor, diluted 5 times with THF, and analyzed using HPLC. Procedure

Organocatalytic asymmetric nitroso aldol reaction of α-substituted malonamates

• Ekta Gupta,
• Narendra Kumar Vaishanv,
• Sandeep Kumar,
• Raja Krishnan Purshottam,
• Ruchir Kant and
• Kishor Mohanan

Beilstein J. Org. Chem. 2022, 18, 217–224, doi:10.3762/bjoc.18.25

• , CDCl3) δ 171.5 (C), 167.0 (C), 147.1 (C), 136.5 (C), 132.1 (CH), 132.1(CH), 128.9 (CH), 128.9 (CH), 126.1 (CH), 122.2 (CH), 122.2 (CH), 121.6 (CH), 121.6 (CH), 117.4 (C), 76.8 (C), 53.5 (CH3), 17.9 (CH3) ppm. The enantiomeric excess was determined by HPLC on a Chiralpak IC column (hexane/ethanol 90:10 v

• silica gel column chromatography. Enantioselectivities were determined by chiral HPLC analysis. Variation of ester moiety of malonamates and nitrosoarenes. General conditions: 1 (0.20 mmol), 2a (0.24 mmol), 3a (0.04 mmol), toluene (3.0 mL). Yields refer to isolated yields after silica gel column

• chromatography. Enantioselectivities were determined by chiral HPLC analysis. aReaction run for 6 h. Synthetic transformation. Optimization of the reaction conditions.a Supporting Information Supporting Information File 202: Detailed experimental procedures, complete characterization data for all compounds

Glycosylated coumarins, flavonoids, lignans and phenylpropanoids from Wikstroemia nutans and their biological activities

• Meifang Wu,
• Xiangdong Su,
• Yichuang Wu,
• Yuanjing Luo,
• Ying Guo and
• Yongbo Xue

Beilstein J. Org. Chem. 2022, 18, 200–207, doi:10.3762/bjoc.18.23

• by a ROESY correlation between H-6'' and H-1'''. Subsequently, an acid hydrolysis of 1 afforded the products including daphnogitin, a ᴅ-glucose, and a ᴅ-xylose. The absolute configurations of glucopyranosyl and xylopyranosyl was further determined by HPLC analysis of the sugar derivatives (Supporting

• the solvent signals. Mass spectra were recorded on a VG Auto Spec-3000 instrument or an API QSTAR Pulsar 1 spectrometer. Semi-preparative HPLC was performed on an Agilent 1120 apparatus equipped with a UV detector and a Zorbax SB-C-18 (Agilent, 9.4 mm × 25 cm) column. Column chromatography was

• and EtOAc. The EtOAc extract (EE) fraction (110 g) was chromatographed over a silica gel (100–200 mesh) column (20 × 100 cm), eluted with dichloromethane/methanol (50:1 to 0:1 v/v) to afford 10 fractions (EE1-EE10). The fraction EE4 (13.3 g) was further purified by semi-preparative HPLC [phenyl column

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

• Estelle Silm,
• Ivar Järving and
• Tõnis Kanger

Beilstein J. Org. Chem. 2022, 18, 167–173, doi:10.3762/bjoc.18.18

• reaction with an electron-donating p-MeO-substituted benzylidene oxindole was very sluggish and did not reach full conversion (Scheme 2, 3m). The product 3m was obtained with only 36% yield and with undetermined enantiomeric purity, since the peaks were not separable in various HPLC methods. Similarly, the

• -protecting groups. Reaction conditions: 0.2 M solution of 1 (1 equiv), 2 (1 equiv), of catalyst D (0.1 equiv), chloroform, at room temperature; isolated yields after column chromatography; ee determined by chiral HPLC. Scope of the reaction (the relative configuration of the major diastereoisomer is depicted

• ). Reaction conditions: 0.2 M solution of 1 equiv of 1, 2 equiv of 2, 0.1 equiv of catalyst D, chloroform, at room temperature; isolated yields after column chromatography; ee determined by chiral HPLC. Comparison reactions of E- and Z-isomers (the relative configurations of the major diastereoisomers are

Synthesis and bioactivity of pyrrole-conjugated phosphopeptides

• Qiuxin Zhang,
• Weiyi Tan and
• Bing Xu

Beilstein J. Org. Chem. 2022, 18, 159–166, doi:10.3762/bjoc.18.17

• second Py unit to give a Boc-capped product, 9. We added guanidinoacetic acid to Py-GGGffpy and (Py)2-GGGffpy for making 10a and 10b, respectively. All the products were purified by HPLC. Bioactivity We examined the cytotoxicity of the synthesized compounds by incubating them with HeLa cells because HeLa

Tenacibactins K–M, cytotoxic siderophores from a coral-associated gliding bacterium of the genus Tenacibaculum

• Yasuhiro Igarashi,
• Yiwei Ge,
• Tao Zhou,
• Amit Raj Sharma,
• Enjuro Harunari,
• Naoya Oku and
• Agus Trianto

Beilstein J. Org. Chem. 2022, 18, 110–119, doi:10.3762/bjoc.18.12

• 50275, Central Java, Indonesia 10.3762/bjoc.18.12 Abstract HPLC/DAD-based chemical investigation of a coral-associated gliding bacterium of the genus Tenacibaculum yielded three desferrioxamine-class siderophores, designated tenacibactins K (1), L (2), and M (3). Their chemical structures, comprising

• three different seawater-based media, and butanolic extracts of the fermented cultures were subjected to HPLC/DAD analysis, which detected several unknown metabolites not present in our in-house UV database, showing UV end-absorption in the culture extract of A11M seawater medium. Purification of these

• reaction monitoring (MRM) mode with the parameter setting “isCID = 0” and “Collision = 45”. An Agilent HP1200 HPLC system equipped with a diode array detector was used for analysis and purification. The absorbance of microtitre plate wells was read on a Thermo Scientific Multiskan Sky microplate reader

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• blocks was developed. Regioisomeric methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates were prepared by the reaction of β-enamino ketoesters (including azetidine, pyrrolidine or piperidine enamines) with hydroxylamine hydrochloride. Unambiguous structural assignments were based on chiral HPLC

• hydroxylamine hydrochloride in methanol (Scheme 1). Synthesized compounds 4b–g exhibited optical activity, and the corresponding (R)- or (S)-enantiomers rotated the plane of plane-polarized light in opposite directions. The enantiomeric purity of chiral compounds 4b–g was assessed via chiral HPLC analysis of

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

• an Agilent 6520 Accurate-Mass Q-TOF MS system equipped with an electrospray ionization (ESI) source. Optical rotations were measured with a Krüss P8000 polarimeter at the indicated concentration with the units of g/100 mL. Enantiomeric excesses were determined by chiral HPLC analysis using an Agilent

• excess (ee) values were determined by HPLC analysis. Substrate scope of barbiturate-based olefins. The reactions were carried out with 1a (0.12 mmol), 2 (0.10 mmol) and catalyst C4 (5 mol %) in solvent (1.0 mL) at room temperature for 12–40 h. The yields refer to isolated products after column

• chromatography. The diastereoisomeric ratios (dr values) were determined by 1H NMR spectroscopy and the enantiomeric excess (ee) values were determined by HPLC analysis. Gram-scale synthesis of 3ah. Further transformation of 3ah. One-pot three-component reaction. Proposed reaction mechanism. Optimization of 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

• . Acknowledgements We thank Andreas Schneider for HPLC purifications and the computing centre of the University of Cologne (RRZK), providing CPU time on the DFG-funded supercomputer CHEOPS. Funding This work was funded by the DFG (DI1536/7-2).

Peptide stapling by late-stage Suzuki–Miyaura cross-coupling

• Hendrik Gruß,
• Rebecca C. Feiner,
• Ridhiwan Mseya,
• David C. Schröder,
• Michał Jewgiński,
• Kristian M. Müller,
• Rafał Latajka,
• Antoine Marion and
• Norbert Sewald

Beilstein J. Org. Chem. 2022, 18, 1–12, doi:10.3762/bjoc.18.1

• peptides P2 to P4 with complete conversion (Scheme 2B). LC–MS analyses revealed broadened or two signals for peptides P1 to P4, which were inseparable by preparative RP-HPLC purification (see Supporting Information File 1). The presence of more than one isomer may be due to the co-existence of

• + 4-position with 4-(2-carboxyethyl)phenylboronic acid followed by on-resin SMC (Scheme 2B). LC–MS analysis revealed two isobaric peaks indicating two isomers, which were largely separable by preparative HPLC with the less polar isomer P5.2 being the major one. The secondary structures of both isomers