An investigation of the rotational isomers of N-acetyl-2,2-dimethyloxazolidine and related compounds by nuclear magnetic resonance spectroscopy and molecular mechanics

1992 ◽  
Vol 70 (1) ◽  
pp. 165-172 ◽  
Author(s):  
Wesley G. Taylor ◽  
Tse Wai Hall ◽  
Carl E. Schreck
Keyword(s):  
Nmr Spectroscopy ◽  
Molecular Mechanics ◽  
Nuclear Overhauser Effect ◽  
Resonance Spectroscopy ◽  
Rotational Isomer ◽  
Rotational Isomers ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Related Compounds ◽  
C Nmr

The 15 2,2-dimethyloxazolidines described here were found to exist in solution predominantly as a single rotational isomer, unlike N-acetyloxazolidine (1), N-acetyl-2-methyloxazolidine (2), N-acetyl-2-(n-octyl)oxazolidine (3), and other known 2-substituted N-acyloxazolidines. Using 13C NMR spectroscopy, activation energies for interconversion of the E (minor) and Z (major) rotational isomers of 1–3 were determined from coalescence temperature measurements in pyridine-d5. A sample of N-acetyl-2,2-dimethyloxazolidine (4) was isolated for comparison. The rotational isomer of 4 was found by two-dimensional nuclear Overhauser effect spectroscopy (NOESY) to possess the Z (or trans) stereochemistry. Molecular mechanics (MMX) calculations on the E and Z isomers of 1–4 helped to account for these findings. The conformation of the energy-minimized structures resembled a C-5 envelope. Samples of N-aroyl-2,2-dimethyloxazolidines (5a–5n) were isolated and the rotational isomers were assigned the Z stereochemistry by NOESY and 13C NMR experiments. Most of these 2,2-dimethyloxazolidines were ineffective in a bioassay for mosquito repellent activity. Keywords: N-acyloxazolidines, N-aroyloxazolidines, NMR spectroscopy, rotational isomerism, molecular mechanics.

scholarly journals Benderamide A, a Cyclic Depsipeptide from a Singapore Collection of Marine Cyanobacterium cf. Lyngbya sp.

Marine Drugs ◽  
2018 ◽  
Vol 16 (11) ◽  
pp. 409 ◽  
Author(s):  
Chi Ding ◽  
Ji Ong ◽  
Hui Goh ◽  
Cynthia Coffill ◽  
Lik Tan
Keyword(s):  
Breast Cancer Cells ◽  
Nuclear Overhauser Effect ◽  
2D Nmr ◽  
Marine Cyanobacterium ◽  
One Dimensional ◽  
Mechanistic Pathway ◽  
Overhauser Effect ◽  
Cyclic Depsipeptide ◽  
Nuclear Overhauser ◽  
Related Compounds

Benderamide A (1), a (S)-2,2-dimethyl-3-hydroxy-7-octynoic acid (S-Dhoya)-containing cyclic depsipeptide that belongs to the kulolide superfamily, was isolated from a Singapore collection of cf. Lyngbya sp. marine cyanobacterium using a bioassay-guided approach. While the planar structure of 1 was elucidated using a combination of 1D and 2D NMR experiments and MS analysis, the absolute configuration was subsequently achieved using the results obtained from Marfey’s analysis, comparative analysis of nuclear overhauser effect spectroscopy (NOESY) with the known compound 3, and one dimensional-nuclear overhauser effect (1D-NOE). Although 1 did not display antiproliferative activity against MCF7 breast cancer cells, the presence of an Ala instead of Gly suggests a possible mechanistic pathway to explain the consequential decrease in cytotoxicity compared to the closely related 2. In addition, results obtained from an LC–MS/MS-based molecular networking algorithm revealed two other closely related compounds encouraging further identification and isolation from the same marine cyanobacterium extract.

scholarly journals In Silico Modeling of Spirolides and Gymnodimines: Determination of S Configuration at Butenolide Ring Carbon C-4

Toxins ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 685
Author(s):  
Christian Zurhelle ◽  
Tilmann Harder ◽  
Urban Tillmann ◽  
Jan Tebben
Keyword(s):  
In Silico ◽  
Density Functional ◽  
Nuclear Overhauser Effect ◽  
Resonance Spectroscopy ◽  
Functional Theory ◽  
Relative Configuration ◽  
Overhauser Effect ◽  
In Silico Modeling ◽  
Nuclear Overhauser

Only few naturally occurring cyclic imines have been fully structurally elucidated or synthesized to date. The configuration at the C-4 carbon plays a pivotal role in the neurotoxicity of many of these metabolites, for example, gymnodomines (GYMs) and spirolides (SPXs). However, the stereochemistry at this position is not accessible by nuclear Overhauser effect—nuclear magnetic resonance spectroscopy (NOE-NMR) due to unconstrained rotation of the single carbon bond between C-4 and C-5. Consequently, the relative configuration of GYMs and SPXs at C-4 and its role in protein binding remains elusive. Here, we determined the stereochemical configuration at carbon C-4 in the butenolide ring of spirolide- and gymnodimine-phycotoxins by comparison of measured 13C NMR shifts with values obtained in silico using force field, semiempirical and density functional theory methods. This comparison demonstrated that modeled data support S configuration at C-4 for all studied SPXs and GYMs, suggesting a biosynthetically conserved relative configuration at carbon C-4 among these toxins.

The isolation and structural elucidation of a new iridoid glycoside from Cymbaria dahurica L.

2018 ◽  
Vol 73 (6) ◽  
pp. 377-379 ◽  
Author(s):  
Cui-Lan Bai ◽  
Qing-Hu Wang ◽  
Yan-Hua Xu ◽  
Jun-Sheng Han ◽  
Yin-Ping Bao
Keyword(s):  
Quantum Coherence ◽  
Nuclear Overhauser Effect ◽  
Multiple Bond ◽  
2D Nmr ◽  
Iridoid Glycoside ◽  
Correlation Spectroscopy ◽  
Etoac Extract ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
C Nmr

AbstractA new iridoid glycoside, namely, cymdahoside A (1), together with two known ones, 2 and 3, were isolated from the EtOAc extract of Cymbaria dahurica. The structure elucidation of 1 was carried out by one-dimensional (1D) NMR (1H and 13C NMR) and 2D NMR (correlation spectroscopy, heteronuclear single-quantum coherence, heteronuclear multiple-bond correlation and nuclear Overhauser effect spectroscopy) spectral analyses.

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