Rotational Spectra of Bicyclic Decanes: The Trans Conformation of (−)-Lupinine

Abstract

The conformational and structural properties of the bicyclic quinolizidine alkaloid (-)-lupinine have been investigated in a supersonic jet expansion using microwave spectroscopy. The rotational spectrum is consistent with a single dominant trans conformation within a double-chair skeleton, which is stabilized by more than 10.4 kJ mol(-1) with respect to other conformations. In the isolated conditions of the jet, the hydroxy methyl side chain of the molecule locks in to form an intramolecular O-H···N hydrogen bond to the electron lone pair at the nitrogen atom. Accurate rotational constants, centrifugal distortion corrections, and (14)N nuclear quadrupole coupling parameters are reported and compared to ab initio (MP2) and DFT (M06-2X) calculations. The stability of lupinine is further compared computationally with epilupinine and decaline in order to gauge the influence of intramolecular hydrogen bonding, absent in these molecules.

Implementation of nuclear gradients of range‐separated hybrid density functionals and benchmarking on rotational constants for organic molecules

“…The test set is extended by the rotational constants of the molecules R ‐(+)‐limonene 10 , (−)‐lupinine 11 , and proline derivative Ac‐Pro‐NH 2 12 , which are depicted along the members of the previous test set in Figure . From the restricted pool of available high‐level experimental data, the molecules were chosen for size and the new structural motifs they provide.…”

Structural and spectral properties of quinolizidine alkaloids: quantum chemical calculations

“…1а) и атома водорода при C(5) соответствует (+)-лупинину [13], тогда как структура эпилупинина с атомом С(5) R-конфигурации и C(6) S-конфигурации отвечает (+)-эпилупинину (2) [14]. Однако в работе [15] полагают, что РСА-анализ [13] подтвердил структуру (-)-лупинина (1), на самом деле имеющего абсолютную R-конфигурацию вышеупомянутых стереоцентров. Результаты наших расчетов и тщательный анализ экспериментальных структурных данных работ [13,14] показали ошибочность мнения авторов [15].…”

“…Однако в работе [15] полагают, что РСА-анализ [13] подтвердил структуру (-)-лупинина (1), на самом деле имеющего абсолютную R-конфигурацию вышеупомянутых стереоцентров. Результаты наших расчетов и тщательный анализ экспериментальных структурных данных работ [13,14] показали ошибочность мнения авторов [15].…”

Inversion of Bicyclic Decanes: Rotational Spectra of the Trans and Double Cis Conformations of 2‐Decalone

“…In the last years microwave spectroscopy has been used for the structural description of some archetypal structural motifs based on saturated fused rings . In particular, we previously examined decalin derivatives like the quinolizidine alkaloids, including the bicyclic lupinine and the tetracyclic sparteine . Decalins are smaller units than functional biochemical building blocks, but they are representative models of the A‐B rings in steroids, and preliminary steps to progress to larger molecules with rotational resolution.…”

“…The study of lupinine first examined a bicyclic decane rotationally, but it observed only the trans ‐ form of the most stable double‐chair configuration, leaving any cis conformation undetected. This preference was partly attributed to an O−H⋅⋅⋅N intramolecular hydrogen bond, enhancing the stability of the global minimum by ca.…”