New variochelins from soil-isolated Variovorax sp. H002

• Jabal Rahmat Haedar,
• Aya Yoshimura and
• Toshiyuki Wakimoto

Beilstein J. Org. Chem. 2024, 20, 692–700, doi:10.3762/bjoc.20.63

• standards (CD3OD: δH 3.31, δC 49.0). LC–MS experiments and ESI–TOF MS/MS analyses were performed with an amaZon SL-NPC (Bruker Daltonics) or LCMS-2020 (Shimadzu) spectrometer coupled with a Shimadzu HPLC system equipped with an LC-20AD intelligent pump. GC–MS experiments were performed with a Shimadzu

Controlling the reactivity of La@C₈₂ by reduction: reaction of the La@C₈₂ anion with alkyl halide with high regioselectivity

• Yutaka Maeda,
• Saeka Akita,
• Mitsuaki Suzuki,
• Michio Yamada,
• Takeshi Akasaka,
• Kaoru Kobayashi and
• Shigeru Nagase

Beilstein J. Org. Chem. 2023, 19, 1858–1866, doi:10.3762/bjoc.19.138

• were calculated using the Gaussian 03 program with DFT at the B3LYP/3-21G for C and H [33], and the LanL2DZ basis set and effective core potential (ECP) for La [29][32]. La@C2v-C82(CH2C6H4CH3) (2a): vis–NIR (CS2): λmax = 572, 741, 1304 nm; MALDI–TOF MS (m/z): [MH]+ calcd for LaC90H9, 1228.98; found

• , 1229.04. La@C2v-C82(CH2C6H4CH3) (3a): vis–NIR (CS2): λmax = 560, 851, 991, 1271 nm; MALDI–TOF MS (m/z): [MH]+ calcd for LaC90H9, 1228.98; found, 1228.99. La@C2v-C82(CH2C6H4CH3) (4a): vis–NIR (CS2): λmax = 525, 986, 1410 nm; MALDI–TOF MS (m/z): [MH]+ calcd for LaC90H9, 1228.98; found, 1229.15. La@C2v-C82

• (CH2C6H4CH3) (5a): vis–NIR (CS2): λmax = 809, 997, 1454 nm; MALDI–TOF MS (m/z): [MH]+ calcd for LaC90H9, 1228.98; found, 1229.04. La@C2v-C82(CH2C6H4CCSi(CH3)3) (2b): vis–NIR (CS2): λmax = 568, 762, 1307 nm; MALDI–TOF MS (m/z): [MH]+ calcd for LaC94H16Si, 1311.01; found, 1311.25. La@C2v-C82(CH2C6H4CCSi(CH3)3

A deep-red fluorophore based on naphthothiadiazole as emitter with hybridized local and charge transfer and ambipolar transporting properties for electroluminescent devices

• Suangsiri Arunlimsawat,
• Patteera Funchien,
• Pongsakorn Chasing,
• Atthapon Saenubol,
• Taweesak Sudyoadsuk and
• Vinich Promarak

Beilstein J. Org. Chem. 2023, 19, 1664–1676, doi:10.3762/bjoc.19.122

• MALDI-TOF-MS techniques. To examine the electronic properties of D–A TPECNz, density functional theory (DFT) calculations at the B3LYP level of theory with the 6-31G(d,p) basis set were performed. It has been previously reported that the twist angle of the D–A segment has a significant role in

Cassane diterpenoids with α-glucosidase inhibitory activity from the fruits of Pterolobium macropterum

• Sarot Cheenpracha,
• Ratchanaporn Chokchaisiri,
• Lucksagoon Ganranoo,
• Sareeya Bureekaew,
• Thunwadee Limtharakul and
• Surat Laphookhieo

Beilstein J. Org. Chem. 2023, 19, 658–665, doi:10.3762/bjoc.19.47

• )-en-12,16-olide (2) [18]. Compound 1 was isolated as an amorphous white powder. The molecular formula was determined as C20H28O3 from the HRESI–TOF–MS analysis with a [M + H]+ ion peak at m/z 317.2107 (calcd C20H29O3, 317.2111) and was considered to have 7 degrees of unsaturation. Its IR absorptions

• colorless oil. The molecular formula was assigned to be C44H60O9 based on the HRESI–TOF–MS analysis with a [M + H]+ ion peak at m/z 733.4305 (calcd for C44H61O9, 733.4310) and NMR data, implying 15 degrees of unsaturation. The IR absorption band at 1724 cm−1 suggested the presence of α,β-unsaturated γ

• ) in the deuterated solvents (CDCl3) using TMS as an internal standard. An Agilent 1290 infinity II/Q-TOFMS mass spectrometer was employed to acquire HRESI–TOF–MS spectra. Column chromatography (CC) was carried out on silica gel 60 (70–230 mesh, Merck, Darmstadt, Germany), and Sephadex LH-20 (GE

Investigation of cationic ring-opening polymerization of 2-oxazolines in the “green” solvent dihydrolevoglucosenone

• Solomiia Borova and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2023, 19, 217–230, doi:10.3762/bjoc.19.21

• ). Obtained data were processed with Win-GPC software. Matrix-assisted laser desorption/ionization time-of-flight mass spectra (MALDI-TOF MS) were recorded on an Autoflex II (Bruker Daltonics, Bremen, Germany) using an N2 laser (λ = 337 nm). All spectra were recorded in positive reflector mode. Detection was

• distributions (ε) and (δ) of low intensity can be attributed to a methyl-initiated and proton-initiated PEtOx formed after termination at position C2 with the final fragmentation of the formed ester group during the MALDI-TOF MS assay carrying Na+ and H+ ions, respectively. It is well known that water and

• obtained via a chain-transfer reaction containing an NHCH=CH2 end group with Na+ (δ). The Mn of the resulting polymers remains lower than expected from the [M]0/[I]0 ratio. As observed in MALDI-TOF MS, the primary molar mass distribution of the resulting polymer after BnBr initiation can be attributed to

A study of the DIBAL-promoted selective debenzylation of α-cyclodextrin protected with two different benzyl groups

• Naser-Abdul Yousefi,
• Morten L. Zimmermann and
• Mikael Bols

Beilstein J. Org. Chem. 2022, 18, 1553–1559, doi:10.3762/bjoc.18.165

• in Table 1. Firstly, reaction with DIBAL in toluene at 0.3 M concentration and at 50 °C gave after 24 h almost complete conversion of the starting material to a symmetrical compound 8 that according to MALDI–TOF MS has lost two DCB groups and not any benzyl group. The compound was analyzed with 1H

Synthesis of protected precursors of chitin oligosaccharides by electrochemical polyglycosylation of thioglycosides

• Md Azadur Rahman,
• Kana Kuroda,
• Hirofumi Endo,
• Norihiko Sasaki,
• Tomoaki Hamada,
• Hiraku Sakai and
• Toshiki Nokami

Beilstein J. Org. Chem. 2022, 18, 1133–1139, doi:10.3762/bjoc.18.117

• obtained at T1 = −60 °C and T2 = −30 °C, although heptasaccharide 7a was not produced. MALDI–TOF MS spectra indicated the formation of byproducts derived from longer oligosaccharides at T1 = −30 °C and T2 = −30 °C (Figure 5). The relative intensity of the molecular ion peaks of hydroxy-substituted sugars

• (T2) on the yield of oligosaccharides. Influence of temperatures of anodic oxidation (T1) and glycosylation (T2). MALDI–TOF MS spectra of oligosaccharides. Proposed structures of byproducts of electrochemical polyglycosylation. Proposed mechanisms of electrochemical polyglycosylation. Oxidative

Synthesis of a new water-soluble hexacarboxylated tribenzotriquinacene derivative and its competitive host–guest interaction for drug delivery

• Man-Ping Li,
• Nan Yang and
• Wen-Rong Xu

Beilstein J. Org. Chem. 2022, 18, 539–548, doi:10.3762/bjoc.18.56

• , 3H); 13C NMR (100 MHz, DMSO-d6, 25 °C) δ 168.55, 148.01, 143.23, 137.64, 126.25, 110.44, 62.71, 62.63, 62.26, 50.89, 27.58; MALDI-TOF MS (m/z) [M + H]+ calcd for C53H49N18O18, 1225.3467; found, 1225.3449 (Δ = −1.5 ppm). Synthesis of compound TBTQ-CB6. Compound 3 (0.27 g, 0.22 mmol) was dissolved in a

• solid (0.28 g, 97%). Mp 198.2–199.4 °C; 1H NMR (400 MHz, D2O, 25 °C) δ 7.89 (s, 6H), 7.21 (s, 6H), 5.25 (s, 12H), 4.97, 4.91 (ABq, J = 17.2 Hz, 12H), 4.31 (s, 3H), 1.57 (s, 3H); 13C NMR (100 MHz, D2O, 25 °C) δ 172.58, 147.37, 143.07, 138.51, 126.22, 110.74, 63.11, 62.15, 61.82, 52.77, 24.69; MALDI-TOF

• MS (m/z) [M – 6NH4 + 6H + Na]+ calcd for C53H48N18O18Na, 1247.3286; found, 1247.3211 (Δ = −6.0 ppm); [M – 6NH4 + 7H]+ calcd for C53H49N18O18, 1225.3467; found, 1225.3252 (Δ = −17.6 ppm), and [M – 6NH4 + 5H + 2 Na]+ calcd for C53H47N18Na2O18, 1269.3106; found, 1269.3199 (Δ = + 7.3 ppm). (a) 1H NMR

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

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

• macrocyclisation product, which was confirmed by MALDI-ToF-MS of the crude reaction mixture after test cleavage (see Supporting Information File 1, Figure S1). However, deboronation and dehalogenation were observed as side reactions to some extent as well as oxidation, most likely of methionine (Met) [79]. The

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

• system (Accela PDA detector, Accela PDA autosampler, and Accela pump) or an Agilent 6540 in ESI-TOF MS coupled to an HPLC Agilent 1290 Infinity equipped with a diode array detector (DAD). Chromatographic fractionation was carried out on a Reveleris preparative flash system equipped with a reversed-phase

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

• distinct. Considering other rDNA regions currently leads to more questions than answers regarding the phylogeny and clearly shows the need for further taxonomic re-evaluation. Experimental General experimental procedures An Agilent 1200 series HPLC-UV system (Santa Clara, CA, USA) with an ESI-TOF-MS (MaXis

Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state

• Xinru Sheng,
• Errui Li and
• Feihe Huang

Beilstein J. Org. Chem. 2020, 16, 2954–2959, doi:10.3762/bjoc.16.245

• . Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF MS) was conducted to investigate the complexation properties. However, no signal related to the complex but only peaks of H were found, implying weak host–guest interactions between H and G (Figures S3 and S4

Changed reactivity of secondary hydroxy groups in C8-modified adenosine – lessons learned from silylation

• Jennifer Frommer and
• Sabine Müller

Beilstein J. Org. Chem. 2020, 16, 2854–2861, doi:10.3762/bjoc.16.234

• Supporting Information File 1). The presence of the modified ribonucleotide in the synthesized sequence was confirmed by MALDI–TOF MS (Figure S1, Supporting Information File 1). Conclusion Oligonucleotides carrying a specific modification or functional entity at a pre-defined position are in high demand for

• equiv TEA, DCM, room temperature, 1 h, 52%. Variation of reaction conditions for 2’-/3’-O silylation of adenosine derivative 7. Supporting Information Supporting Information File 434: Experimental procedures, RNA synthesis, characterization data (1H, 13C NMR, MALDI–TOF MS, PAGE), copies of 1H and 13C

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• ; doublet, d; doublet-doublet, dd; doublet-triplet, dt; triplet, t; multiplet, m. High-resolution mass spectra (HRMS) were recorded at Gazi University Faculty of Pharmacy using electron ionization (EI) mass spectrometry (Waters-LCT-Premier-XE-LTOF (TOF-MS) instruments; in m/z (rel. %). Elemental analysis

Six-fold C–H borylation of hexa-peri-hexabenzocoronene

• Mai Nagase,
• Kenta Kato,
• Akiko Yagi,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2020, 16, 391–397, doi:10.3762/bjoc.16.37

• –Ishiyama borylation step is possibly increased by further conditions screening. The thus-obtained 1 was identical to the product from the C–H borylation of HBC according to 1H NMR spectroscopy, and the 13C NMR and HRMS by MALDI–TOF MS results also supported the identification. The hexaborylated HBC 1 was

• JEOL JMS-S3000 SpiralTOF (MALDI–TOF MS). Nuclear magnetic resonance (NMR) spectra were recorded on a JEOL ECS-600 (1H 600 MHz, 13C 150 MHz) spectrometer or a JEOL ECA 600II spectrometer with UltraCoolTM probe (1H 600 MHz, 13C 150 MHz). Chemical shifts for 1H NMR are expressed in parts per million (ppm

• (1.1 mg, 0.8% yield based on 2) as an orange solid. 1H NMR (600 MHz, CDCl3) δ 9.78 (s, 1H), 1.61 (s, 6H); 13C NMR (150 MHz, CDCl3) δ 25.6, 84.4, 122.4, 127.0, 127.3, 128.8, 129.9; HRMS (MALDI–TOF MS) m/z: [M]+ calcd for C78H84B6O12, 1278.6571; found, 1278.6582. X-ray crystallography Details of the

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• ring. Finally, branching is evidenced by the discrepancy in molecular weight as calculated for a linear polymer by 1H NMR compared with that indicated by MALDI–TOF MS (Figure 2). Due to the high regioselectivity in small molecule couplings, defects to this extent were unexpected. MALDI–TOF MS was

• Scheme 1. The region from 4–4.5 ppm indicates the interior indole repeat units compared with the terminal indole units. MALDI–TOF MS of PIn, indicating octylindole repeat units with three different types of end groups. These include 2-nitrophenyl, iodine, and hydrogen. A high yielding, highly selective

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• in DMF for the synthesis of P2. However, in the case of P1 and P3, the formation of tetramethylguanidinium side products was detected by MALDI–TOF MS. This irreversible N-guanylation of the polyamide N-terminus resulted from slow carboxy activation of the building block by HBTU and the presence of an

• 2.5% TFA in dichloromethane. The free C-terminus of the polyamides was modified in solution with N,N-dimethylaminopropylamine by using PyBOP as an activating reagent to install the corresponding end group. The completeness of all reaction stages was checked by MALDI–TOF MS. Purification of the final

Skeletocutins M–Q: biologically active compounds from the fruiting bodies of the basidiomycete Skeletocutis sp. collected in Africa

• Tian Cheng,
• Clara Chepkirui,
• Cony Decock,
• Josphat C. Matasyoh and
• Marc Stadler

Beilstein J. Org. Chem. 2019, 15, 2782–2789, doi:10.3762/bjoc.15.270

• , solvent A: H2O + 0.1% formic acid, solvent B: acetonitrile + 0.1% formic acid, elution gradient: 5% solvent B for 0.5 min, increasing solvent B to 100% within 19.5 min, 100% solvent B for 5 min, flow rate: 0.6 mL/min, UV–vis detection at λ = 200–600 nm) and ESI–TOF–MS analysis (maXis™ system, Bruker, scan

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• , even at increased reaction times. Minor products with more downfield chemical shifts were also observed via 1H NMR of these crude product mixtures; these were easily separated from quaterphenyl isomers using flash column chromatography. Analysis of the crude product mixtures by MALDI–TOF–MS confirmed

• through time-of-flight matrix assisted laser desorption ionization (MALDI–TOF–MS) mass spectrometry, using sulfur as a matrix. Suzuki–Miyaura coupling to form m,p’-quaterphenyl (13) [35]: 4-Biphenylboronic acid (0.18 g, 0.91 mmol) and 1 M K2CO3 (1.5 mL) were added to a 10 mL Pyrex microwave tube. 3

• the general rearrangement procedure. The crude product was purified via CombiFlash with hexanes to yield an off-white solid (7 mg, 70% yield) consisting of 13 (81%) and 14 (19%). Minor products were eluted with ethyl acetate. MALDI–TOF–MS analysis indicated oligomerization (m/z = 344, 673). o,m

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• solvents. Mass spectra (ESI-TOF-MS) were measured by using a Bruker micrOTOFII-AGA1. All reagents were purchased from TCI, Wako Co. Ltd., Aldrich Chemical Company, Inc. and Kanto Chemical Co., Inc., and were used without further purification. The synthetic procedure of Benzil-PIC is shown in Scheme 2. The

• isomers), 7.33–7.30 (m, 4H, two structural isomers), 7.07–7.04 (m, 4H, two structural isomers), 6.73–6.69 (m, 4H, two structural isomers); ESI-TOF MS m/z: [M + H]+ calcd for C35H24N2O3: 521.1859691; found, 521.1836034. Benzil-PIC A solution of potassium ferricyanide (0.968 g, 2.94 mmol) and KOH (0.741 g

• , 1H), 7.31–7.29 (m, 2H), 7.16 (d, J = 7.7 Hz, 1H), 6.64 (d, J = 10.0 Hz, 2H), 6.36 (d, J = 10.0 Hz, 2H); ESI-TOF MS m/z: [M + H]+ calcd for C35H22N2O3, 519.1703190; found, 519.1696883. Experimental setups Steady-state measurements Steady-state absorption spectra were measured with an UV-3600 Plus

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• follows: s (singlet); d (doublet); dd (double doublet); t (triplet); q (quartet); m (multiplet) and br (broad). Chemical shifts are denoted in δ (ppm) referenced to the residual protic solvent peaks. Coupling constants J are denoted in Hz. Mass spectra were recorded on a MALDI-Spiral-TOF-MS mass

Isolation of fungi using the diffusion chamber device FIND technology

• Benjamin Libor,
• Henrik Harms,
• Stefan Kehraus,
• Ekaterina Egereva,
• Max Crüsemann and
• Gabriele M. König

Beilstein J. Org. Chem. 2019, 15, 2191–2203, doi:10.3762/bjoc.15.216

• , MeOH); UV (MeOH) λmax (log ε): 203 (4.0), 261 (3.5) nm; CD (c 4.0 × 10−3 M, MeOH) λmax (Δ ε) 203 (1.33), 207 (1.21), 213 (−0.57), 321 (−0.75); IR νmax: 3648, 2930, 1706, 1683, 1558, 1540, 1507, 1435, 1376, 1237, 634 cm−1; HRESI-TOF-MS m/z: [M + H]+ calcd for C15H21O3 249.1481; found, 249.1485. For 1H

• , 1376, 1237, 1037, 634 cm−1; HRESI-TOF-MS m/z: [M + H]+ calcd for C15H23O3 251.1641; found, 251.1642. For 1H and 13C NMR data see Supporting Information File 1, Table S5. Agar diffusion assay Culture plates (5% sheep blood Columbia agar, BD) were overlaid with 3 mL tryptic soy soft agar, inoculated with

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS)

• Philipp P. Könen and
• Matthias Wüst

Beilstein J. Org. Chem. 2019, 15, 1945–1961, doi:10.3762/bjoc.15.190

• ) coupled to a time-of-flight mass spectrometer (TOF–MS) after headspace-solid phase microextraction (HS-SPME). The identification of structurally complex natural compounds, such as sesquiterpenes from fruits and vegetables, is often reported as “tentative”, as authentic standards are not commercially

• the unlabeled and deuterated compounds, mechanisms for sesquiterpene formation in V. vinifera could be proposed and already known pathways could be confirmed or disproved. For example, the HS-SPME–GC×GC–TOF–MS measurements of fed sample material showed that the tricyclic sesquiterpene hydrocarbons α

• -copaene, β-copaene, α-cubebene, β-cubebene and the bicyclic δ-cadinene were biosynthesized via (S)-(−)-germacrene D rather than via (R)-(+)-germacrene D as intermediate. Keywords: biosynthesis; deuterium labeling; germacrene; HS-SPME; terpenes; TOF–MS; Introduction The aroma profile of grape berries at

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• ESI/APCI as an ion source and a manual pump for sampling. Matrix-assisted laser desorption ionization–time-of-flight mass spectra (MALDI–TOF MS) were measured on a MALDI–TOF MS UltrafleXtreme (Bruker Daltonics) and samples were ionized with the aid of a Nd:YAG laser (355 nm) from α-cyano-4