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ACD/Labs Blog

Arvin Moser
Part of the process of interpreting data from 2D NMR spectra is to adjust the intensity threshold in order to differentiate visually the signals from the noise. A certain level of cautious peak picking is needed so not to overlook a weak signal nor confuse a noisy region for a real signal. For an unknown...

Arvin Moser
Spectral data that exhibit weak signals (low S/N) can easily be misinterpreted. A good approach is to check the data against other data to confirm whether the signal is real or an artefact. For an unknown compound, the 1H -13C HSQC spectrum below is shown at two different intensity thresholds. The aromatic protons at 6.97...

Arvin Moser
With deuterated chloroform, the signals from the solvent can overlap with the signals from the unknown of interest. The following spectra are some examples one may encounter. In the expanded regions for each 13C NMR spectrum, Cases 1, 2, 3, 4 and 5 display a weak signal at ~76.8, 77.3, 77.5, 77.5, 77.5 ppm, respectively....

Mikhail Elyashberg
A recent article highlighted the isolation and structure elucidation of a new natural product Psychotripine (molecular formula C33H34N6), which exhibited a complex carbon skeleton comprised of 11 rings. We attempted the Computer-Assisted Structure Elucidation (CASE) of Psychotriptine using only the original limited and incomplete NMR data gathered from the original publication

Arvin Moser
Solvent signals that overlap with signals from the unknown can be a hurdle in an elucidation. The energy wasted when misidentifying a signal can make an elucidation attempt wearisome and frustrating to put it mildly. Several 13C NMR spectra were collected in deuterated chloroform for a set of unknown compounds. Are any non-solvent signals evident...

Arvin Moser
Given a set of data points, the elucidator aims to conjure up a variety of scenarios that are consistent with the data at hand. This puzzle aims to draw out an unlikely, but worth considering, scenario that needs to be verified. The expanded region for the 1H-13C HSQC-DEPT spectrum presents two scenarios that are consistent...

Mikhail Elyashberg
Philip Williams and co-workers isolated a new cytotoxic peptide, Tasiamide B (molecular formula C50H74N8O12) containing the unusual amino acid-derived residue 4-amino-3-hydroxy-5-phenylpentanoic acid. The structure of the peptide was determined through a combination of 2D NMR experiments and HPLC analysis of degradation products. The experimental data was submitted to the Structure Elucidator Challenge to determine if the software could propose the same structure.

Arvin Moser
For this puzzle, the objective is to extract structural information from the NMR data. However, the underlying message is to check all possible atomic combinations so that no plausible fragment gets overlooked. For an unknown compound, an expanded region of the 1H-13C HSQC-DEPT spectrum below shows two 1H multiplets and two negatively-phased correlations (blue). The...

Arvin Moser
For the past decade, I had the privilege to be involved in a global project aimed at elucidating unknowns from a variety of clients. The purpose of this project was to explore and expand the utility of a Computer-Assisted Structure Elucidation (CASE) software. It is because of this project that the idea for the blog...

Mikhail Elyashberg
Robert Capon and co-workers identified two new nematocidal depsipeptides, identified as phoriospongins A (molecular formula C52H82N11O15Cl) and B. The structures of the phoriospongins were determined by detailed spectroscopic analysis and comparison with the previously reported sponge depsipeptide cyclolithistide A. The experimental data was submitted to the Structure Elucidator Challenge to determine if the software could propose the same structure.

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