MDPI - Publisher of Open Access Journals

10 pages, 1899 KiB

Open AccessCommunication

Butyl (2,2-Dibutoxybutanoyl)-ʟ-Tryptophanate

by Diego Quiroga and Ericsson Coy-Barrera

Molbank 2024, 2024(1), M1794; https://doi.org/10.3390/M1794 - 19 Mar 2024

Viewed by 1610

The multicomponent reaction between ʟ-tryptophan 1, 2-oxobutanoic acid 2, and 1-butanol in the presence of SiMe₃Cl was studied using microwave irradiation conditions. The main product was identified as an unreported acetal-containing compound, namely, butyl (2,2-dibutoxybutanoyl)-ʟ-tryptophanate (3), yielding 89%. NMR experiments demonstrated that the adjacent methylene protons of the acetal group appeared as two signals exhibiting their behavior as diastereotopic protons. DFT/B3LYP calculations revealed an asymmetric molecular structure with specific angles, leading to an explanation of the NMR results. The calculated chemical shifts showed slight differences with the experimental values and suggested magnetic anisotropy and inductive deprotection around the methylene hydrogen atoms in the acetal location. The reaction mechanism was proposed in which SiMe₃Cl plays a crucial role by promoting water removal through key steps. Full article

(This article belongs to the Section Organic Synthesis and Biosynthesis)

► Show Figures

Figure 1

15 pages, 7563 KiB

Open AccessArticle

An Examination of Factors Influencing Small Proton Chemical Shift Differences in Nitrogen-Substituted Monodeuterated Methyl Groups

by Stuart J. Elliott, O. Maduka Ogba, Lynda J. Brown and Daniel J. O’Leary

Symmetry 2021, 13(9), 1610; https://doi.org/10.3390/sym13091610 - 2 Sep 2021

Cited by 1 | Viewed by 3311

Abstract

Monodeuterated methyl groups have previously been demonstrated to provide access to long-lived nuclear spin states. This is possible when the

{CH}_{2} D

rotamers have sufficiently different populations and the local environment is chiral, which foments a non-negligible isotropic chemical shift difference between [...] Read more.

Monodeuterated methyl groups have previously been demonstrated to provide access to long-lived nuclear spin states. This is possible when the

{CH}_{2} D

rotamers have sufficiently different populations and the local environment is chiral, which foments a non-negligible isotropic chemical shift difference between the two CH

_{2}

D protons. In this article, the focus is on the N-

{CH}_{2} D

group of N-

{CH}_{2} D

-2-methylpiperidine and other suitable

{CH}_{2} D

-piperidine derivatives. We used a combined experimental and computational approach to investigate how rotameric symmetry breaking leads to a

^{1}

{CH}_{2} D

chemical shift difference that can subsequently be tuned by a variety of factors such as temperature, acidity and 2-substituted molecular groups. Full article

(This article belongs to the Special Issue Symmetry Principles in the Nuclear Magnetic Resonance)

► Show Figures

Figure 1

33 pages, 20368 KiB

Open AccessReview

Symmetry Breaking in NMR Spectroscopy: The Elucidation of Hidden Molecular Rearrangement Processes

by Michael J. McGlinchey

Symmetry 2014, 6(3), 622-654; https://doi.org/10.3390/sym6030622 - 4 Aug 2014

Cited by 11 | Viewed by 14998

Abstract

Variable-temperature NMR spectroscopy is probably the most convenient and sensitive technique to monitor changes in molecular structure in solution. Rearrangements that are rapid on the NMR time-scale exhibit simplified spectra, whereby non-equivalent nuclear environments yield time-averaged resonances. At lower temperatures, when the rate of exchange is sufficiently reduced, these degeneracies are split and the underlying “static” molecular symmetry, as seen by X-ray crystallography, becomes apparent. Frequently, however, such rearrangement processes are hidden, even when they become slow on the NMR time-scale, because the molecular point group remains unchanged. Judicious symmetry breaking, such as by substitution of a molecular fragment by a similar, but not identical moiety, or by the incorporation of potentially diastereotopic (chemically non-equivalent) nuclei, allows the elucidation of the kinetics and energetics of such processes. Examples are chosen that include a wide range of rotations, migrations and other rearrangements in organic, inorganic and organometallic chemistry. Full article

(This article belongs to the Special Issue Chemical Applications of Symmetry)

► Show Figures

Graphical abstract

18 pages, 180 KiB

Open AccessReview

Diastereoselective Desymmetrization of Symmetric Dienes and its Synthetic Application

by Kenji Nakahara and Hiromichi Fujioka

Symmetry 2010, 2(2), 437-454; https://doi.org/10.3390/sym2020437 - 25 Mar 2010

Cited by 16 | Viewed by 7658

Abstract

The desymmetrization of symmetric compounds is a useful approach to obtain chiral building blocks. Readily available precursors with a prochiral unit could be converted into complex molecules with multiple stereogenic centers in a single step. In this review, recent advances in the desymmetrization [...] Read more.

(This article belongs to the Special Issue Feature Papers: Symmetry Concepts and Applications)

► Show Figures

Graphical abstract

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI