Biochemical and structural characterisation of the second oxidative crosslinking step during the biosynthesis of the glycopeptide antibiotic A47934

• Veronika Ulrich,
• Clara Brieke and
• Max J. Cryle

Beilstein J. Org. Chem. 2016, 12, 2849–2864, doi:10.3762/bjoc.12.284

• Scientific, Waltham, USA) and the calculated extinction coefficient of the protein at λ = 280 nm. Furthermore, the protein identity was confirmed by MALDI–TOF MS peptide map fingerprinting of a tryptic digest of excised protein bands from SDS-PAGE analysis. StaF was finally stored in SEC buffer in aliquots

Synthesis and characterization of fluorinated azadipyrromethene complexes as acceptors for organic photovoltaics

• Forrest S. Etheridge,
• Roshan J. Fernando,
• Sandra Pejić,
• Matthias Zeller and
• Geneviève Sauvé

Beilstein J. Org. Chem. 2016, 12, 1925–1938, doi:10.3762/bjoc.12.182

• analogs for the synthesis of L3 and L4 were synthesized according to literature procedures and used without purification [35][36]. The Stille cross coupling reactions for the synthesis of L3 and L4 were monitored by MALDI–TOF–MS and were found to not be complete after increasing the reaction time to 48 h

• spectroscopy, MALDI–TOF–MS and elemental analysis. In the case of L2, the pure BF2+ chelate could not be isolated by column chromatography, and will therefore be omitted from further analysis. The thermal stability of the zinc(II) complexes was examined by thermal gravity analysis and the results are shown in

• spectra were recorded using a 500 MHz Bruker Ascend Avance III HDTM equipped with ProdigyTM ultra-high sensitivity Multinuclear Broadband CryoProbe or a Varian 400 MHz spectrometer in parts-per-million with respect to tetramethylsilane. MALDI–TOF–MS samples were prepared from chloroform solutions in a

Effect of the π-conjugation length on the properties and photovoltaic performance of A–π–D–π–A type oligothiophenes with a 4,8-bis(thienyl)benzo[1,2-b:4,5-b′]dithiophene core

• Ni Yin,
• Lilei Wang,
• Yi Lin,
• Jinduo Yi,
• Lingpeng Yan,
• Junyan Dou,
• Hai-Bo Yang,
• Xin Zhao and
• Chang-Qi Ma

Beilstein J. Org. Chem. 2016, 12, 1788–1797, doi:10.3762/bjoc.12.169

• solar cells based on COOP-nHT-TBDT at different blend ratios, a J–V comparison of devices based on 4:PC61BM and 4:PC71BM, UV–vis absorption spectra of COOP-nHT-TBDT:PC61BM blended films, as well as the NMR and MALDI–TOF MS spectra of COOP-nHT-TBDT. Supporting Information File 274: Additional

Automated glycan assembly of a S. pneumoniae serotype 3 CPS antigen

• Markus W. Weishaupt,
• Stefan Matthies,
• Mattan Hurevich,
• Claney L. Pereira,
• Heung Sik Hahm and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2016, 12, 1440–1446, doi:10.3762/bjoc.12.139

• of the glycosylation solutions exiting the reaction chamber was tested and found to be strongly acidic. After cleavage from the solid support, HPLC analysis of the crude product showed one major product (Figure 4). However, MALDI–TOF MS analysis indicated that this fraction corresponded to a

3,6-Carbazole vs 2,7-carbazole: A comparative study of hole-transporting polymeric materials for inorganic–organic hybrid perovskite solar cells

• Wei Li,
• Munechika Otsuka,
• Takehito Kato,
• Yang Wang,
• Takehiko Mori and
• Tsuyoshi Michinobu

Beilstein J. Org. Chem. 2016, 12, 1401–1409, doi:10.3762/bjoc.12.134

• , 28.74, 27.71, 27.32, 26.96, 26.73, 24.27, 22.96, 17.37, 13.94, 13.58, 13.48, 10.75, 9.59 ppm; FTIR (neat) ν: 2955, 2923, 2852, 2361, 1798, 1652, 1614, 1581, 1462, 1419, 1376, 1342, 1276, 1258, 1218, 1143, 1063, 1014, 961, 867, 794, 749, 698, 679, 654, 624, 607 cm−1; MALDI–TOF MS (Mw = 859.4): m/z

• , 14.00, 11.21, 10.08, 7.84 ppm; FTIR (neat) v: 2955, 2923, 2870, 2852, 1485, 1458, 1441, 1415, 1376, 1339, 1319, 1250, 1200, 1146, 1071, 996, 962, 911, 860, 826, 814, 794, 741, 723, 710, 695, 653, 633, 616 cm−1; MALDI–TOF MS (Mw = 859.4): m/z = 860.5 ([M + H]+). Synthesis of 3,6-Cbz-EDOT Analogously to

Artificial Diels–Alderase based on the transmembrane protein FhuA

• Hassan Osseili,
• Daniel F. Sauer,
• Klaus Beckerle,
• Marcus Arlt,
• Tomoki Himiyama,
• Tino Polen,
• Akira Onoda,
• Ulrich Schwaneberg,
• Takashi Hayashi and
• Jun Okuda

Beilstein J. Org. Chem. 2016, 12, 1314–1321, doi:10.3762/bjoc.12.124

• oxidized to Cu(II) by contamination with air. Cu(II) led to protein aggregation and precipitation. This was shown in an independent experiment. When one equiv of Cu(NO3)2·3H2O was added to a solution of FhuA ΔCVFtev, the protein precipitated rapidly and quantitatively. MALDI–TOF–MS analysis for the whole

• catalyst 17 was successful. Comparison of the MALDI–TOF– MS spectrum with FhuA ΔCVFtev (calcd (M + Na+): m/z = 5925 Da; found: m/z = 5925 Da) indicates successful coupling. The signal of m/z = 6301 Da indicates the FhuA fragment with the attached ligand framework (calcd (M): m/z = 6302 Da; found: m/z

• = 6301 Da). The signal of m/z = 6111 Da results from saponification of the ester and the maleimide moiety (calcd (M + H2O + Na+): m/z = 6111 Da, found: m/z = 6111 Da). We were unable to detect the copper ion in the MALDI–TOF–MS. The isolated biohybrid catalysts were tested in the Diels–Alder reaction of

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• up, ranging from 200 000 g/mol to over 400 000 g/mol (Mn). Importantly, in all these cases very high conversion is observed. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–ToF MS) and NMR experiments clearly show that BnOH is incorporated in the resulting PDMS (S1

Cholesterol lowering effects of mono-lactose-appended β-cyclodextrin in Niemann–Pick type C disease-like HepG2 cells

• Keiichi Motoyama,
• Yumi Hirai,
• Rena Nishiyama,
• Yuki Maeda,
• Taishi Higashi,
• Yoichi Ishitsuka,
• Yuki Kondo,
• Tetsumi Irie,
• Takumi Era and
• Hidetoshi Arima

Beilstein J. Org. Chem. 2015, 11, 2079–2086, doi:10.3762/bjoc.11.224

• , lactose was modified to NH2-β-CyD using the reducing agent cyanotrihydroborate in dimethyl sulfoxide (DMSO) at room temperature for 24 h. No unreacted free lactose was confirmed by thin-layer chromatography (TLC). The MALDI–TOF MS spectrum of Lac-β-CyD showed a peak at m/z 1483 derived from lactose mono

• for protons at 25 °C. The concentration of the sample was 1.5 mg/750 μL in deuterated oxide (D2O), and the chemical shifts were given as parts per million (ppm) downfield from that of tetramethylsilane (TMS). MALDI-TOF mass spectra (MALDI–TOF MS) were measured in a positive mode at 25 °C by a JEOL JMS

• with Scheffe's test. The level of statistical significance was set at p < 0.05. Preparation scheme of Lac-β-CyD. MALDI–TOF MS (A) and 1H NMR (B) spectra of Lac-β-CyD. Cytotoxic activity of β-CyDs in U18666A-treated HepG2 cells after treatment for 24 h. U18666A-treated HepG2 cells were incubated with

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics

• Alexander L. Kanibolotsky,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2015, 11, 1749–1766, doi:10.3762/bjoc.11.191

• ) revealed by GPC analysis (Table 2) corresponds to about 7 thienoTTF monomer units per polymer chain for 35 and 37, and about 6 units for 39. MALDI–TOF MS characterisation was only successful for polymer 39 and showed a series of peaks with a mass difference of 516 Da, corresponding to the mass of the 2

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• , 107.5 ppm; anal. calcd for C12H7NOS4: C, 46.58; H, 2.28; N, 4.53; found: C, 46.16; H, 2.22; N, 4.43; MALDI–TOF MS calcd: m/z = 309.5. found: m/z = 308.9 [M]+; HRMS (M): calcd for C12H7NOS4: 308.9410; found: 308.9413. 5-([2,2’-Bi(1,3-dithiolylidene)]-4-yl)picolinaldehyde (2): This compound was prepared

• , 131.8, 130.8, 122.6, 122.5, 120.7, 120.6, 114.2, 105.7 ppm; anal. calcd for C12H7NOS4: C, 46.58; H, 2.28; N, 4.53; found: C, 46.54; H, 2.20; N, 4.51; MALDI–TOF MS calcd: m/z = 309.5. found: m/z = 308.9 [M]+. HRMS (M): calcd for C12H7NOS4: 308.9410; found: 308.9404. 2-([2,2’-Bi(1,3-dithiolylidene)]-4-yl

• . calcd for C18H11N5O4S4: C, 44.15; H, 2.26; N, 14.30, found: C, 43.54; H, 2.22; N, 13.66; MALDI–TOF MS calcd: m/z = 489.6. found: m/z = 489.1 [M]+; HRMS (M): calcd for C18H11N5O4S4: 488.9694; found: 488.9687. 5-([2,2’-bi(1,3-dithiolylidene)]-4-yl)-2-((2,4-dinitrophenyl)hydrazono)methyl)pyridine (L2

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

• Flavia Pop and
• Narcis Avarvari

Beilstein J. Org. Chem. 2015, 11, 1105–1111, doi:10.3762/bjoc.11.124

• TMS. The following abbreviations are used: d, doublet; t, triplet; m, multiplet. MALDI–TOF MS spectra were recorded on a Bruker Biflex-IIITM apparatus, equipped with a 337 nm N2 laser. Elemental analyses were recorded using Flash 2000 Fisher Scientific Thermo Electron analyzer. The starting compounds

• chromatography using petroleum spirit/dichloromethane 1:1 followed by dichloromethane as eluent, to afford an orange solid (0.53 g, 48%). 1H NMR (300 MHz, CDCl3) δ 3.23–3.17 (m, 2H, -CH-CH3), 3.06 (t, 2H, -CH2-), 2.71 (t, 2H, -CH2-), 1.42 (d, 6H, -CH3) ppm; MALDI–TOF MS (m/z): [M − CH2CH2CN)]+ 437.4; Anal. calcd

• , 116.56, 112.02, 111.44, 50.10, 44.04, 30.38, 27.39, 21.36 ppm; MALDI–TOF MS (m/z): 444 [M]+ (Mcalcd = 443.86); Anal. calcd for C12H12O2S8: C, 32.41; H, 2.72; O, 7.19; S, 57.68; found: C, 32.72; H, 2.55; O, 6.95; S, 57.93 (%). (R,R)-1: The same synthetic procedure was followed as for the (S,S)-enantiomer

Terminal lipophilization of a unique DNA dodecamer by various nucleolipid headgroups: Their incorporation into artificial lipid bilayers and hydrodynamic properties

• Emma Werz and
• Helmut Rosemeyer

Beilstein J. Org. Chem. 2015, 11, 913–929, doi:10.3762/bjoc.11.103

• purchased from Roth (D-Karlsruhe). All lipo-oligonucleotides 10–15 (Figure 2) were synthesized, purified and characterized by MALDI–TOF mass spectrometry by Eurogentec SA (B-Liege). In each case, the detected mass confirmed the corresponding calculated mass. MALDI–TOF–MS (m/z): 4636.8 (10, [M + H]+; calcd

Exploring monovalent and multivalent peptides for the inhibition of FBP21-tWW

• Lisa Maria Henning,
• Sumati Bhatia,
• Miriam Bertazzon,
• Michaela Marczynke,
• Oliver Seitz,
• Rudolf Volkmer,
• Rainer Haag and
• Christian Freund

Beilstein J. Org. Chem. 2015, 11, 701–706, doi:10.3762/bjoc.11.80

• according to the published procedure [19] (see Figures S2 and S3 in Supporting Information File 1 for GPC and MALDI–TOF–MS analysis of the hPG-OH core). Seventy percent of all hydroxy groups (≈120 OH groups) on hPG-OH were functionalized with amino groups in a three-step protocol as reported in the

Trifluoromethyl-substituted tetrathiafulvalenes

• Olivier Jeannin,
• Frédéric Barrière and
• Marc Fourmigué

Beilstein J. Org. Chem. 2015, 11, 647–658, doi:10.3762/bjoc.11.73

• des Substances Naturelles (ISCN), Gif/Yvette (France). MALDI-TOF MS spectra were obtained from a Bruker Biflex-IIITM equipped with a 337 nm laser. Syntheses Preparation of EDT-TTF(CONH2)(CF3) (7): EDT-TTF(CO2Me)(CF3) (2bc) [17] (0.2 g, 0.47 mmol) was added to a MeOH solution (20 mL) saturated with

Redox active dendronized polystyrenes equipped with peripheral triarylamines

• Toshiki Nokami,
• Naoki Musya,
• Tatsuya Morofuji,
• Keiji Takeda,
• Masahiro Takumi,
• Akihiro Shimizu and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2014, 10, 3097–3103, doi:10.3762/bjoc.10.326

• dendronized polystyrene 8a was characterized using MALDI–TOF MS analysis. Six peak groups were observed, as shown in Figure 4. The peak occurring at 10,573 Da [M + Ag+] is derived from 11 dendritic substituents (815 Da × 11), 14 styrene units (103 Da × 11 + 104 Da × 3), and a butyl group (58 Da), which was

• ). Preparation of dendronized polystyrenes having peripheral diarylamino groups. MALDI–TOF MS analysis of the dendronized polystyrene with peripheral bromo groups. Cyclic voltammograms of dendronized polystyrene 9 (black line), model compound 10 (blue line), and the film of dendronized polystyrene 9 (red line

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

• Diego Cortizo-Lacalle,
• Calvyn T. Howells,
• Upendra K. Pandey,
• Joseph Cameron,
• Neil J. Findlay,
• Anto Regis Inigo,
• Tell Tuttle,
• Peter J. Skabara and
• Ifor D. W. Samuel

Beilstein J. Org. Chem. 2014, 10, 2683–2695, doi:10.3762/bjoc.10.283

• through a PureSolv purification system. 1H and 13C NMR spectra were recorded at room temperature on a Bruker DRX500 at 500 and 125 MHz or a Bruker Avance 400 instrument at 400 and 100 MHz; chemical shifts are given in ppm and all J values are in Hz. MALDI–TOF–MS were recorded on a Shimadzu Axima-CFR

A versatile δ-aminolevulinic acid (ΑLA)-cyclodextrin bimodal conjugate-prodrug for PDT applications with the help of intracellular chemistry

• Chrysie Aggelidou,
• Theodossis A. Theodossiou,
• Antonio Ricardo Gonçalves,
• Mariza Lampropoulou and
• Konstantina Yannakopoulou

Beilstein J. Org. Chem. 2014, 10, 2414–2420, doi:10.3762/bjoc.10.251

• the HSQC-edited spectrum (Supporting Information File 1, Figure S3). The ratio 8 to 4 was ~3, as indicated by integration of the respective signals and also confirmed by MALDI–TOF MS measurements (m/z 1853, Supporting Information File 1, Figure S4), whereas the IR spectrum exhibited the characteristic

Synthesis and immunological evaluation of protein conjugates of Neisseria meningitidis X capsular polysaccharide fragments

• Laura Morelli,
• Damiano Cancogni,
• Marta Tontini,
• Alberto Nilo,
• Sara Filippini,
• Paolo Costantino,
• Maria Rosaria Romano,
• Francesco Berti,
• Roberto Adamo and
• Luigi Lay

Beilstein J. Org. Chem. 2014, 10, 2367–2376, doi:10.3762/bjoc.10.247

• subsequently reconstituted with 10 mM NaPi pH 7. Yields (recovered glycoprotein as determined by microBCA, Pierce Thermo): 85–95%. Loading of glycoconjugate was determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI–TOF MS; UltraFlex III MALDI–TOF/TOF instrument

Oligomerization of optically active N-(4-hydroxyphenyl)mandelamide in the presence of β-cyclodextrin and the minor role of chirality

• Helmut Ritter,
• Antonia Stöhr and
• Philippe Favresse

Beilstein J. Org. Chem. 2014, 10, 2361–2366, doi:10.3762/bjoc.10.246

• NMR spectroscopy because of the different induced shift of the protons which became diastereotopic through complexation [11][12]. Actually, the chirality discrimination of 1 with RAMEB-CD is evident from the different induced shift of the protons 8 at 5.2 ppm (zoomed out in Figure 1). The MALDI–TOF MS

• enzymatic oligomerization consists of up to 10 repetitive units which could be detected by MALDI–TOF MS measurements. Furthermore comparable molecular weights are accessible through oligomerization of 1 with iron(II)-salen as catalyst. Here oligomers 2 with up to 8 repetitive units are detectable. The

• mol−1, D = 1.15; (RS)-2: 1H NMR (300 MHz, DMSO-d6) δ 10.11–9.92 (m, 1H, -NH), 9.40–9.31 (m, 1H, -OH), 7.84–6.89 (overlapping multiplets, 7H, -ArH), 6.51–6.34 (m, 1H, -OH), 5.15–5.01 (m, 1H, -CH) ppm. 2D ROESY NMR spectrum (600 MHz, D2O) of the racemate 1 complexed with RAMEB-CD. MALDI–TOF MS spectrum

Specific DNA duplex formation at an artificial lipid bilayer: fluorescence microscopy after Sybr Green I staining

• Emma Werz and
• Helmut Rosemeyer

Beilstein J. Org. Chem. 2014, 10, 2307–2321, doi:10.3762/bjoc.10.240

• -hydroxymethylpropane-1,3-diol (TRIS) were purchased from Roth (Karlsruhe, Germany). All oligonucleotides 4–10 (Figure 1) were synthesized, purified and characterized by MALDI–TOF mass spectrometry by Eurogentec SA (Liege, Belgium). In each case the detected mass confirmed the corresponding calculated mass. MALDI–TOF

• –MS (m/z): 4247.7 (4, [M + H]+; calcd 4247.4); 4178.4 (5, [M + H]+; calcd 4178.1); 3645.5 (6, [M + H]+; calcd 3644.5); 4248.1(7, [M + H]+; calcd 4247.4); 3643.2 (8, [M + H]+; calcd 3644.46); 7306.4 (9, [M + H]+; calcd 7312.9); 6076.4 (10, [M + H]+; calcd 6077.6). 4 5’-d(1a-p-TAG GTC AAT ACT)-3’ 5 5’-d

Synthesis and optical properties of pyrrolidinyl peptide nucleic acid carrying a clicked Nile red label

• Nattawut Yotapan,
• Chayan Charoenpakdee,
• Pawinee Wathanathavorn,
• Boonsong Ditmangklo,
• Hans-Achim Wagenknecht and
• Tirayut Vilaivan

Beilstein J. Org. Chem. 2014, 10, 2166–2174, doi:10.3762/bjoc.10.224

• under different sequence context, were successfully synthesized and characterized by MALDI–TOF MS (Figure 1 and Table 1). Isolated yields in the range of 6–18% were obtained (0.5 μmol scale), which are typical for solid phase synthesis, whereby the majority of material loss occurred during HPLC

Multivalent scaffolds induce galectin-3 aggregation into nanoparticles

• Candace K. Goodman,
• Mark L. Wolfenden,
• Pratima Nangia-Makker,
• Anna K. Michel,
• Avraham Raz and
• Mary J. Cloninger

Beilstein J. Org. Chem. 2014, 10, 1570–1577, doi:10.3762/bjoc.10.162

• functionalized dendrimers were characterized by MALDI–TOF–MS (matrix-assisted laser desorption time of flight mass spectrometry). The average numbers of sugars that were incorporated are shown in Scheme 2. The loadings were determined by both the changes in weight average molecular weight (Mw) upon addition of 1

Staudinger ligation towards cyclodextrin dimers in aqueous/organic media. Synthesis, conformations and guest-encapsulation ability

• Malamatenia D. Manouilidou,
• Yannis G. Lazarou,
• Irene M. Mavridis and
• Konstantina Yannakopoulou

Beilstein J. Org. Chem. 2014, 10, 774–783, doi:10.3762/bjoc.10.73

• dissolution of 2 or 3 were observed evidently due to secondary reactions leading to a lower yield for the ligation step. Monomer 4 and dimer 6 displayed a single 31P NMR signal at 35.2 ppm and the correct mass in MALDI–TOF MS. Reaction of 4 with mono(6-15N-amino-6-deoxy)-β-CD under typical amide coupling

Tuning the interactions between electron spins in fullerene-based triad systems

• Maria A. Lebedeva,
• Thomas W. Chamberlain,
• E. Stephen Davies,
• Bradley E. Thomas,
• Martin Schröder and
• Andrei N. Khlobystov

Beilstein J. Org. Chem. 2014, 10, 332–343, doi:10.3762/bjoc.10.31

• ), 70.85, 69.31, 60.22, 57.07 (sp3 carbons, 4 environments); MALDI–TOF MS (DCTB/MeCN, m/z): 1580.2 (M−); IR (KBr, ν, cm−1): 2960 (w), 2922 (w), 1645 (s), 1453 (w), 1328 (m), 1186 (m), 746 (m), 526 (s); UV–vis (CS2): λmax (ε × 10−3/dm3 mol−1 cm−1): 703 (0.750), 433 (8.526). Synthesis of 6 [70

• , 128.40 (sp2 carbons, 80 environments), 71.84, 69.68, 68.74, 64.10, 62.67, 62.63 (sp3 carbons, 6 environments); MALDI–TOF MS (DCTB/MeCN, m/z): 1820.5; IR (KBr, ν, cm−1): 2932 (m), 2363 (s), 1663 (s, C=O), 1435 (m), 669 (s); UV–vis (CS2): λmax (ε × 10−3/dm3 mol−1 cm−1): 693 (3.74), 556 (20.32), 476 (39.28

• , 145.40, 145.31, 144.64, 144.60, 143.45, 143.22, 143.07, 142.78, 142.18, 142.03, 140.60, 140.38, 139.15, 137.17, 134.25, 133.75, 132.92 (sp2 carbons, 52 environments), 74.22, 73.26, 70.50, 68.18, 68.14, 64.51, 63.11 (sp3 carbons, 7 environments); MALDI–TOF MS (DCTB/MeCN, m/z): 1686.3; IR (KBr, ν, cm−1

Oligomeric epoxide–amine adducts based on 2-amino-N-isopropylacetamide and α-amino-ε-caprolactam: Solubility in presence of cyclodextrin and curing properties

• Julian Fischer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 2803–2811, doi:10.3762/bjoc.9.315

• spectrometry (ESIMS) was conducted on a Bruker maXis 4G mass spectrometer and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS) on a Bruker Dalomics Ultraflex 1 mass spectrometer. Melting points were obtained using a Büchi Melting Point B-545 apparatus at a heating