NMR elucidation of some pentacycloundecane derived ligands

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The synthesis and NMR elucidation of five novel penta-cycloundecane amine derivatives are reported. These compounds are potential antituberculosis agents. The (1)H and (13)C spectra showed major overlapping of methine signals of the cage skeleton making it extremely difficult to elucidate these compounds. The overlapping occurs as a result of the additions made to the carbonyl carbon (C-8/C-11) of the cage. The two-dimensional NMR technique proved to be a useful tool in overcoming this problem. All compounds reported are meso compounds thereby not only simplifying the NMR structure elucidation, but also making it indeed possible.

Section: Resultsmentioning

confidence: 99%

Synthesis and NMR elucidation of novel penta‐cycloundecane amine derivatives as potential antituberculosis agents

Onajole

Govender

Makatini

et al. 2008

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“…The assignment procedure for all PCU compounds (1-8) was analogous to those described before [19,21] and the results are presented in Tables 1 and 2. The C-N bond in compounds 1 and 2 experiences partial double-bond character which hinders 'free' rotation of the sp 2 amide nitrogen. Thus for compound 1, the cis-amide proton (δ = 7.33 ppm) to the carboxamide oxygen appears at a higher frequency compared to the trans-amide proton (δ = 7.08 ppm) due to a through-space deshielding effect of the cis-proton.…”

Section: Resultsmentioning

confidence: 99%

“…[10,21] Compound 12 was converted to its corresponding diacid chloride [10] and reacted with ammoniasaturated chloroform at 0…”

Section: Introductionmentioning

confidence: 99%

Synthesis and NMR assignment of pentacycloundecane precursors of potential pharmaceutical agents

Onajole

Makatini

Gasqui

et al. 2010

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The synthesis and complete NMR elucidation of eight novel pentacycloundecane (PCU) derivatives are reported. These compounds are precursors in the synthesis of PCU-based anti-tuberculosis (TB) agents and potential human immunodeficiency virus (HIV) protease inhibitors. Two-dimensional (2D) NMR techniques were used to assign the NMR spectra for these compounds. Substitution of the cage molecule at (C-8/11) further complicates the assignment, since some of the substituted alkyl chain groups overlap with the cage proton signals. The side chain heteroatoms also introduce a rare through-space deshielding effect to some of the carbon atoms of the cage skeleton. Ring strain in the rigid cage skeleton appears to induce drastic electronic changes in some parts of the cage framework. This observation is more dramatic for the C-4 methylene group of the cage diols and the cage ethers.

“…When the heteroatoms on the side arms are positioned in close proximity to the cage, it induces a through-space deshielding effect resulting in nonequivalence of atoms on the cage and that of the 'arm' similar to observations in previous reports of related chiral PCU ligands. [9,11] The infrared (IR) spectrum of 1 displays a sharp N-H absorption at 3312 cm −1 , and methyl absorptions at 2949 and 2929 cm −1 ; the absorption at 1646 cm −1 confirms the presence of the amide bond. The mass spectrum of 1 exhibits the correct molecular ion peak at m/z 741.4118 ([M + H] + ).…”

Section: Resultsmentioning

confidence: 99%

“…The PCU dione 6 was converted to the 3,5-diallyl-4-oxahexacyclo[5.4.1.0 2,6 .0 3,10 .0 5,9 .0 8,11 ]dodecane 7 as described previously. [15,16] This diene 7 is an intermediate in the synthesis of all the derivatives 1-5 being investigated.…”

Section: Introductionmentioning

confidence: 99%

NMR elucidation of a novel (S)‐pentacyclo‐undecane bis‐(4‐phenyloxazoline) ligand and related derivatives

Boyle

Govender

Kruger

et al. 2008

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The NMR elucidation of a novel ligand (S)-pentacyclo-undecane bis-(4-phenyloxazoline) and related pentacyclo-undecane (PCU) derivatives is reported. Two-dimensional NMR proved to be a powerful technique in overcoming the difficulties associated with the elucidation of these compounds when only one-dimensional NMR data is utilized. A chiral substituent was introduced to both 'arms' of the PCU skeleton to produce derivatives 1-3. These derivatives display C(1) symmetry with all thecage atoms being nonequivalent. Owing to overlapping of peaks in the (1)H spectra, identification of these diastereomeric protons was very difficult. The (13)C spectra gave rise to clear splitting of the nonequivalent carbons. This is unusual compared to similar PCU derivatives with chiral substituents as splitting of all the diastereomeric cage carbons has not yet been reported. Nuclear Overhauser enhancement spectroscopy (NOESY) correlations of derivatives 1-3 confirm the different conformations of the molecule in which the side 'arms' occupy different orientations with respect to cage moiety.