Heteronuclear Multibond Correlation Research Articles

Hyaluronic acid conjugates of glycine peptides and L-tryptophan

This work reports about the conjugation of glycine C-terminal ethyl and methyl ester peptides and L-tryptophan methyl ester with sodium hyaluronate in aqueous solutions using the peptide coupling agent DMTMM (or short DMT, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride). Detailed infrared (IR) absorbance and 1H and 13C (2D) NMR studies (heteronuclear multi-bond correlation spectroscopy, HMBC) confirmed covalent and regioselective amide bonds with the D-glucuronate, but also proves the presence of DMT traces in all conjugates. The ethyl ester`s methyl protons on the peptides` C-terminal could be used to quantify the degree of substitution of the peptide on the hyaluronate scaffold by NMR. The ester group also proved stable during conjugation and work-up, and could in some cases be selectively cleaved in water whilst leaving the amide bond intact as shown by potentiometric charge titration, NMR and IR. The conjugates did not influence the capability of human umbilical vein endothelial cells (HUVECs) to reduce MTS (5-[3-(carboxymethoxy)phenyl]-3-(4,5-dimethyl-2-thiazolyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt) to a formazan dye, which points towards a low cytotoxicity for the obtained products. The conjugation method and products could be tested for tissue engineering gels or drug delivery purposes with alternative, biologically active peptides.

Cytotoxic Long-chain Alkene and Terpene Isolated from the Methanol Extract of the Air-dried Leaves of Pipturus arborescens C.B. Rob

A long-chain alkene (1-hexacosene) and a terpene were obtained from the bioactive methanol extract of the air-dried leaves of Pipturus arborescens (Link) C.B. Rob (“Handalamay”) collected from Poblacion, Kapatagan, Lanao del Norte. The compounds were isolated through extraction with ethanol, sequential partitioning with water-chloroform and hexane-90% methanol followed by fractionation and purification with repeated gravity column chromatography using gradient mixtures of hexane: ethyl acetate (1:1 ratio). The structures of the isolates were elucidated on the basis of spectroscopic data: 1 H-and 13 C-NMR, 1 H- 13 C Heteronuclear Multiquantum Correlation (HMQC), 1 H- 13 C Heteronuclear Multibond Correlation (HMBC), 1 H- 1 H Homonuclear Correlation Spectroscopy (COSY), Infra-Red Spectroscopy (IR), Ultraviolet-Visible Spectroscopy (UV-VIS) and Mass Spectrometry (MS). The isolated compounds were shown to possess moderate cytotoxic activity against the brine shrimp Artemia salina (Leach).

Synthesis and structure elucidation of 25,26,27,28-tetramethylcalix[4]arene tetraketone using 1D and 2D NMR spectroscopies

The 1H and 13C NMR spectra of the new calix[4]arene-based tetraketone were completely assigned by one- and two-dimensional homo- and heteronuclear experiments ( 1H– 1H COSY, 1H– 13C HMQC, and HMBC) at 400 and 100 MHz, respectively, at 25 °C standard pulse sequence. 1H and 13C spectra were measured at room temperature for 25,26,27,28-tetramethylcalix[4]arene tetraketone ( 1). 13C{ 1H}, DEPT and NMR techniques were used to distinguish the methyl, methylene and methine carbon resonance signals of calix[4]arene 1. Correlation of 1D ( 1H, 13C{ 1H}, DEPT) and 2D (HMQC and HMBC) NMR data was used to completely assign various overlapping and broad signals of calix[4]arene 1. Heteronuclear multibond correlation (HMBC) studies were used to completely assign various carbon resonances. Our results show that the conformation of calix[4]arene 1 in the solution is very similar to the cone conformation reported in the literature.

Structure Elucidation of a Pyrazolo[3,4]pyran Derivative by NMR Spectroscopy

The structure of a representative pyrazolo[3,4]pyran derivative was determined by 1D and 2D NMR techniques. Complete 1H and 13C chemical shifts for this compound are reported. Careful analysis of the HMBC (Heteronuclear Multi-Bond Correlation) spectrum helped to elucidate the configuration of the derivative around C7 and C8. The results showed that the characteristic double-strong and double-weak cross peak pattern in the HMBC spectrum for C7 and C8 might be useful for establishing the structures of other pyrazolo[3,4]pyran derivatives.

Microstructure determination of 9-ethyl-3-hydroxymethylcarbazolyl acrylate/methacrylonitrile using two-dimensional NMR spectroscopy

Solution polymerization was carried out using AIBN as initiator at 60 °C and varying the molar infeed ratio to get different composition of 9-ethyl-3-hydroxymethylcarbazolyl acrylate-co-methacrylonitrile (C/N). The molecular weight was determined using gel-permeation chromatography (GPC). Differential scanning calorimetry (DSC) was used to determine the glass transition temperature ( T g). 13C{ 1H}, DEPT-45, 90 and 135 NMR techniques were used to distinguish the α-methyl, methine, backbone methylene and quaternary carbon resonance signals of C/N copolymers. Correlation of 1D ( 1H, 13C{ 1H}, DEPT) and 2D (HSQC, TOCSY, HMBC) NMR data were used to completely assign various overlapping and broad signals of C/N copolymers. Heteronuclear multi bond correlation (HMBC) studies were used to completely assign various nitrile resonances. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be r C = 0.31 ± 0.03 and r N = 0.80 ± 0.02 whereas those calculated from RREVM method were found to be r C = 0.35 and r N = 0.83, respectively.

Structural investigations of (9-ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate copolymers using two-dimensional NMR spectroscopy

(9-Ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate (E/A) copolymers of different compositions were prepared by solution polymerization by varying the molar infeed ratio, using AIBN as initiator at 60°C. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be rE = 1.16 ± 0.02 and rA = 0.69 ± 0.01 whereas those calculated from RREVM method were found to be rE = 1.18 and rA = 0.68. The molecular weights (Mw) and polydispersity index (PDI, Mw/Mn) were determined using gel permeation chromatography (GPC). Glass transition temperatures (Tg) for different compositions of E/A copolymers were determined using differential scanning calorimetry (DSC). Copolymer molar outfeed ratio (FE) was calculated from 1H NMR spectra. The α-methyl, methine, backbone methylene, and quaternary carbon resonance signals of the copolymers were distinguished using 13C{1H}, DEPT-45, -90, and -135 NMR techniques. The α-methyl and β-methylene showed compositional and configurational sensitivity up to pentad and tetrad level, respectively, whereas methine showed only compositional sensitivity up to pentad level. Unambiguous assignments for 1H and 13C{1H} NMR spectra were done by correlating 1D (1H, 13C{1H}, DEPT) and 2D (HSQC, TOCSY) NMR data. The spectral assignments for carbonyl region were done by studying higher bond order couplings by heteronuclear multibond correlation (HMBC) spectra. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5595–5606, 2006

Microstructure analysis of methyl acrylate/methyl methacrylate copolymers by two‐dimensional NMR spectroscopy. II

AbstractIn the present article, a comprehensive two‐dimensional heteronuclear multi bond correlation (HMBC) spectral analysis of methyl acrylate (A)/methyl methacrylate (B) copolymers is reported. The methylene carbon and methine carbon resonances assigned from the 2D HSQC spectroscopy were established by analyzing the two and three bond order couplings with α‐methyl protons, methylene protons, and methine protons. Quaternary carbon resonances of the B unit were assigned by investigating the two bond order couplings with α‐methyl protons and methylene protons. Assignments of carbonyl carbon resonances based on the analysis of three bond couplings with α‐methyl protons and methylene protons are reported. The analyses present comprehensive assignments of the carbonyl carbon resonances showing the critical contribution of 2D HMBC spectroscopy in the indirect analysis of carbon resonances. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Atom transfer radical copolymerizationof acrylonitrile/n‐butyl acrylate: Microstructure determination by two‐dimensional nuclearmagnetic resonance spectroscopy

AbstractAtom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n‐butyl acrylate copolymers were synthesized with 2‐bromopropionitrile as the initiator and CuCl/Cu(0)/2,2′‐bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number‐average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative 13C{1H} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao–Huglin terminal model were rA = 1.30 and rB = 0.68 for acrylonitrile and n‐butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen–Tudos method were rA = 1.29 ± 0.01 and rB = 0.67 ± 0.01. 13C{1H} NMR and distortionless enhancement by polarization transfer (DEPT‐45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one‐dimensional (1H, 13C{1H}, and DEPT) and two‐dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2810–2825, 2005

Structural investigations of poly(methyl methacrylate) by two-dimensional NMR

In the present paper a comprehensive microstructure analysis of PMMA based on the combination of one-dimensional and two-dimensional (TOCSY, HSQC, and HMBC) NMR experiments is reported. To resolve complex resonance assignments, empirical chemical shift modeling supported by the 2D NMR spectroscopy has been done. Rigorous assignments of resonance signals have been done by investigating the one bond couplings between carbon/proton nuclei by the HSQC (heteronuclear single quantum coherence) and two bond proton/proton couplings by TOCSY (total correlation spectroscopy) experiments. Investigations of the two and three bond order carbon/proton couplings from HMBC (heteronuclear multi bond correlation) spectrum are reported.

SmI2/Sm-Based γ-Buyrolactone−ε-Caprolactone Copolymers: Microstructural Characterization Using One- and Two-Dimensional NMR Spectroscopy

Copolymers containing nonhomopolymerizable γ-butyrolactone (BL) and e-caprolactone (CL) units of different compositions were synthesized by the ring-opening polymerization method using the SmI2/Sm initiator system. A maximum of 33 mol % of BL was incorporated into polycaprolactone (PCL) backbone. The microstructure of these copolymers was analyzed by one- and two-dimensional NMR spectroscopies. The overlapped methylene proton signals of CL and BL were resolved using 2D 1H−13C heteronuclear multibond correlation (HMBC) and homonuclear 1H−1H total correlation spectroscopy (TOCSY) techniques. The triad sequence distribution centered at the carbonyl carbon and methylene carbon of CL and BL has been obtained from 13C NMR spectroscopy. Further, 1D and 2D NMR spectroscopic techniques were used to confirm the change of microstructure from PCL blocks separated by discrete BL units to random copolymer structure having BL−BL units with increase in the mole percent of BL units in the copolymer.

Synthesis of acetyl,docosahexaenoyl-glycerophosphocholine and its characterization using nuclear magnetic resonance.

Docosahexaenoic acid (DHA) circulates in mammals in lipoproteins and bound to serum albumin as a nonesterified fatty acid as well as esterified in lysophosphatidylcholine (lysoPC). 1-Lyso,2-DHA-glycerophosphocholine (GPC) is an unstable isomer because of a primary alcohol at the sn-1 position. To keep DHA at the sn-2 position of lysoPC, its usual position for the corresponding lysoPC to be acylated into PC in tissues, we synthesized 1-acetyl,2-DHA-GPC and confirmed its structure by use of nuclear magnetic resonance (NMR) spectroscopy in comparison with its positional isomer, 1-DHA,2-acetyl-GPC. 1-Lyso,2-DHA-GPC was prepared from 1-stearoyl,2-DHA-GPC by enzymatic hydrolysis and purified by high-performance liquid chromatography. The isomerization of 1-lyso,2-DHA-GPC into 1-DHA,2-lyso-GPC was obtained by keeping the former overnight at room temperature under nitrogen. Both lysoPC isomers were acetylated by acetic anhydride into 1-acetyl,2-DHA-GPC and 1-DHA,2-acetyl-GPC, respectively, and the resulting phospholipids were fully characterized by NMR. In particular, the 1,2 substitution pattern of the acetyl and DHA chains could be easily detected by 2D heteronuclear multibond correlation. We conclude that 1-acetyl,2-DHA-GPC might be considered as a stable form of 1-lyso,2-DHA-GPC for its delivery to tissues, if the latter exhibits acetyl hydrolase activity.

A Synthesis of 1-Azaanthraquinones via Diels-Alder Reaction of 4-Hydroxy- and 4-Methoxy-2-phenylquinolinequinones with 3-Trimethylsilyloxy-1,3-butadienes: Observation of Inverse Regioselectivity.

Diels-Alder reaction of 4-hydroxy-2-phenylquinolinequinone (10a) and 4-methoxy-2-phenylquinoline-quinone (10b) with 1-methoxy-3-trimethylsilyloxybutadiene proceeded in a highly regio- and stereoselective manner to give the [4+2] adducts (11) and (14) in good yields, respectively. The structures of the adducts and their derivatives were unambiguously determined by spectroscopic data, including high resolution heteronuclear multi bond correlation. The quinolinequinones (10a and 10b) gave inverse regioselectivity. This is related to the presence of the hydroxy group or the methoxy group at the C-4 position. These results demonstrated that Diels-Alder reaction of azadienophiles with activated dienes provides a versatile method for synthesizing 4-oxygenated 1-azaanthraquinones.