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Beyond optical rotation: what's left is not always right in total synthesis.

ABSTRACT: This work describes the application of vibrational (VCD) and electronic (ECD) circular dichroism spectroscopy to solve the longstanding debate around the absolute configuration of (+)-frondosin B (1). The absolute configuration of (+)-1 could confidently be assigned as (R) using these spectroscopic techniques. The discrepancy in the optical rotation (OR) values obtained in previous studies can be attributed to an undetected minor impurity (ca. 7%) that arose unexpectedly in a key step late in the synthesis. Additionally, the conditions used in the final step of the previous reports for demethylation to form the natural product proceeded with significant loss of enantiopurity. The large OR measured for the impurity at its observed level, when compared to the small rotation for the less enantiopure natural product 1, led to a measured OR value for the synthetic material that had the opposite sign of the natural product.

SUBMITTER: Joyce LA

PROVIDER: S-EPMC5868320 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Beyond optical rotation: what's left is not always right in total synthesis.

Joyce Leo A LA Nawrat Christopher C CC Sherer Edward C EC Biba Mirlinda M Brunskill Andrew A Martin Gary E GE Cohen Ryan D RD Davies Ian W IW

Chemical science 20171030 2

This work describes the application of vibrational (VCD) and electronic (ECD) circular dichroism spectroscopy to solve the longstanding debate around the absolute configuration of (+)-frondosin B (1). The absolute configuration of (+)-1 could confidently be assigned as (R) using these spectroscopic techniques. The discrepancy in the optical rotation (OR) values obtained in previous studies can be attributed to an undetected minor impurity (ca. 7%) that arose unexpecte ...[more]

PMID: 29629112

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Project description:BackgroundBased on Euler/Cardan analysis, prior investigations have reported up to 80° of glenohumeral (GH) external rotation during arm elevation, dependent on the plane of elevation (PoE). However, the subtraction of Euler/Cardan angles does not compute the rotation around the humerus' longitudinal axis (i.e. axial rotation). Clinicians want to understand the true rotation around the humerus' longitudinal axis and rely on laboratories to inform their understanding of underlying shoulder biomechanics, especially for the GH joint since its motion cannot be visually ascertained. True GH axial rotation has not been previously measured in vivo, and its difference from Euler/Cardan (apparent) axial rotation is unknown.Research questionWhat is the true GH axial rotation during arm elevation and external rotation, and does it vary from apparent axial rotation and by PoE?MethodsTwenty healthy subjects (10 M/10 F, ages 22-66) were recorded using biplane fluoroscopy while performing arm elevation in the coronal, scapular and sagittal planes, and external rotation in 0° and 90° of abduction. Apparent GH axial rotation was computed using the xz'y'' and yx'y'' sequences. True GH axial rotation was computed by integrating the projection of GH angular velocity onto the humerus' longitudinal axis. One-dimensional statistical parametric mapping was utilized to compare apparent versus true axial rotation, axial rotation versus 0°, and detect differences in axial rotation by PoE.ResultsIn contrast to apparent axial rotation, true GH axial rotation does not differ by PoE and is not different than 0° during arm elevation at higher elevation angles. The spherical area between the sequence-specific and actual humeral trajectory explains the difference between apparent and true axial rotation.SignificanceProper quantification of axial rotation is important because biomechanics literature informs clinical understanding of shoulder biomechanics. Clinicians care about true axial rotation, which should be reported in future studies of shoulder kinematics.

Dataset Information

Beyond optical rotation: what's left is not always right in total synthesis.

Publications

Beyond optical rotation: what's left is not always right in total synthesis.

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