Division of Environmental Materials Science, Graduate School of Environmental Science, Hokkaido University, N10W5, Kita-ku, Sapporo 060-0810, Japan.
Hiroshima Synchrotron Radiation Center (HiSOR), Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima 739-0046, Japan.
Molecules. 2021 Feb 27;26(5):1296. doi: 10.3390/molecules26051296.
A new application of vacuum-ultraviolet circular dichroism (VUVCD), which enables the measurement of CD spectra in the vacuum-ultraviolet region (140-200 nm), for the assignment of the absolute configurations of bromoallenes is described. Bromoallene moieties are found in natural products obtained from many marine organisms. To date, the absolute configuration of bromoallenes has been assigned almost exclusively with Lowe's rule, which is based on specific rotation. However, exceptions to Lowe's rule have been reported arising from the presence of other substituents with large specific rotations. For the unambiguous assignment of the absolute configuration of the bromoallene moiety with its characteristic absorption wavelength at 180-190 nm due to the π-π* transition, VUVCD was applied to four pairs of bromoallene diastereomers prepared by modifying the synthetic scheme of omaezallene. The VUVCD spectra clearly showed positive or negative Cotton effects around 180-190 nm according to the configuration of the bromoallene employed, revealing the potential of VUVCD for determining absolute stereochemistry.
本文描述了真空紫外圆二色性（VUVCD）的一种新应用，该应用可用于测量真空紫外区域（140-200nm）的 CD 光谱，从而确定溴代丙二烯的绝对构型。溴代丙二烯部分存在于从许多海洋生物中获得的天然产物中。迄今为止，溴代丙二烯的绝对构型几乎完全是根据基于比旋光度的 Lowe 规则来确定的。然而，据报道，由于存在具有较大比旋光度的其他取代基，Lowe 规则也存在例外。为了明确确定溴代丙二烯部分的绝对构型，该部分在 180-190nm 处具有特征吸收波长，这是由于π-π*跃迁引起的，因此应用 VUVCD 对通过修改 omaezallene 的合成方案制备的四对溴代丙二烯非对映异构体进行了研究。VUVCD 光谱根据所采用的溴代丙二烯的构型，在 180-190nm 附近清晰地显示出正或负的 C otton 效应，这表明 VUVCD 具有确定绝对立体化学的潜力。
