Systematic Comparison of Sets of ¹³C NMR Spectra That Are Potentially Identical. Confirmation of the Configuration of a Cuticular Hydrocarbon from the Cane Beetle Antitrogus parvulus

Abstract

A systematic process is introduced to compare 13C NMR spectra of two (or more) candidate samples of known structure to a natural product sample of unknown structure. The process is designed for the case where the spectra involved can reasonably be expected to be very similar, perhaps even identical. It is first validated by using published 13C NMR data sets for the natural product 4,6,8,10,16,18-hexamethyldocosane. Then the stereoselective total syntheses of two candidate isomers of the related 4,6,8,10,16-pentamethyldocosane natural product are described, and the process is applied to confidently assign the configuration of the natural product as (4S,6R,8R,10S,16S). This is accomplished even though the chemical shift differences between this isomer and its (16R)-epimer are only ±5–10 ppb (±0.005–0.01 ppm).

Disentangling Complex Mixtures of Compounds with Near‐Identical 1H and 13C NMR Spectra using Pure Shift NMR Spectroscopy

“…[1] Severala pproaches have been reported for discerning compounds with very similar NMR spectra. [2,3] In this work we present as imple but very useful experimental NMR strategy that greatlyf acilitates the analysiso fh ighly congested spectral regions. We will show here how am ixture of compounds with near-identical 1 Ha nd 13 CNMR spectra can be distinguished using high-resolution NMR methods based on the combination of pure shift NMR [4][5][6][7][8][9][10] and spectral aliasing techniques.…”

Enantioselective Total Synthesis of Antibiotic CJ-16,264, Synthesis and Biological Evaluation of Designed Analogues, and Discovery of Highly Potent and Simpler Antibacterial Agents

“…The latter was obtained from known iodide 80 18 through a stereoselective process involving ephedrine propionate 81 . 19 Thus, alkylation of 81 (LDA, LiCl) with citronellyl iodide ( 80 ) 18 furnished amide 82 (85% yield), which was reductively cleaved with H 3 N·BH 3 in the presence of LDA to afford primary alcohol 83 in excellent diastereoselectivity (72% yield). DMP oxidation of the latter furnished aldehyde 84 (82% yield).…”

Single‐Step Construction of the anti‐Deoxypropionate Motif from Propylene: Formal Total Synthesis of the Cuticular Hydrocarbons Isolated from Antitrogus parvulus

“…This strategy was applied to the facile formal total synthesis of the major cuticular hydrocarbons, (4 S ,6 R ,8 R ,10 S ,16 R ,18 S )‐4,6,8,10,16,18‐hexamethyldocosane ( 2 ) and (4 S ,6 R ,8 R ,10 S ,16 S )‐4,6,8,10,16‐pentamethyldocosane ( 3 ), isolated from the cane beetle Antitrogus parvulus . The racemic mixture of the common synthetic intermediate of 2 and 3 , that is rel ‐(2 R ,4 S ,6 R ,8 S )‐2,4,6,8‐tetramethylundecan‐1‐ol [(±)‐ 4 ], was successfully obtained in a single step.…”

“…After optimizing the reaction conditions in the 5 /MAO/ZnEt 2 system, we switched our focus to the natural product synthesis to demonstrate the synthetic utility of our new strategy. The target alcohol (±)‐ 4 , which was previously synthesized over at least 11 steps, can be synthesized in a single step by syndiospecific propylene oligomerization using di( n ‐propyl)zinc as a chain‐transfer agent and subsequent oxidation after oligomerization.…”

“…Thus, single‐step synthesis of (±)‐ 4 is achieved and this sequence is the shortest ever reported. Consequently, the facile formal total syntheses of 2 and 3 were also achieved.…”