Cyclase enzymes weave simple polyprenyl chains into the elaborate polycyclic ring systems of terpenes, a sequence that is often difficult to emulate under abiotic conditions. Here we report a disparate synthetic approach to complex terpenes whereby simple prenyl-derived chains are cyclized using radical, rather than cationic, reaction pathways. This strategy allowed us to efficiently forge the intricate 5-8-5 fused ring systems found in numerous complex natural product classes and also enabled a nine-step total synthesis of (–)-6- epi- ophiobolin N, a member of the large family of cytotoxic ophiobolin sesterterpenes. A small-molecule thiol catalyst was found to override the inherent diastereoselectivity observed during a reductive radical cascade cyclization process. This work lays the foundation for efficient synthesis of terpenoid ring systems of interest in medicinal research, particularly those that have been historically challenging to access.

/pdf/enantioselective-synthesis-of-an-ophiobolin-sesterterpene-53a0cf96vl.pdf

Enantioselective synthesis of an ophiobolin sesterterpene via a programmed radical cascade.

Applications of allylamines for the syntheses of aza-heterocycles ☆

Organoboron compounds are highly valuable in synthetic chemistry. In particular, α-borylcarbonyl compounds have shown versatile synthetic applications, owing to fruitful chemistries of both the boryl and carbonyl moieties. However, the synthesis of these molecules still remains tedious and time-consuming. Here we report a straightforward and practical route to synthesize α-borylcarbonyl molecules based on a regioselective radical α-borylation of α,β-unsaturated carbonyl compounds. The reaction features unusual α-regioselectivity and high functional-group compatibility. Further synthetic applications of new α-borylated products were also demonstrated. DFT and kinetic studies implicated that the α-regioselectivity of β-aryl-α,β-unsaturated carbonyl compounds was determined by the thermodynamically more favorable radical α-addition step, whereas the formation of α-addition products from β-alkyl-α,β-unsaturated carbonyl compounds was driven by an energetically favored hydrogen atom transfer step. Given that α,β-unsaturated carbonyl compounds can be easily obtained in abundance and variety, this method enjoys great advantages in diverse and economical synthesis of valuable α-borylcarbonyl molecules. α-Borylcarbonyl compounds are versatile synthons in organic synthesis, however their preparation is often tedious. Here, the authors report a regioselective radical α-borylation of α,β-unsaturated carbonyl compounds to afford α-borylcarbonyl molecules with high selectivity and functional group compatibility.

/pdf/regioselective-radical-a-borylation-of-a-b-unsaturated-3hcs3edku6.pdf

Regioselective radical α-borylation of α,β-unsaturated carbonyl compounds for direct synthesis of α-borylcarbonyl molecules

Total synthesis of (+)-decursivine.

The radical cyclization reactions of unsaturated sulfonamides were investigated. The photolysis of N-(4-halo-4-pentenyl)sulfonamides (X = I, Br, or Cl) with (diacetoxyiodo)benzene (DIB) and iodine at room temperature afforded exclusively the corresponding piperidines in 73−98% yield via 6-endo radical cyclization. On the other hand, the reactions of N-(5-halo-4-pentenyl)sulfonamides with DIB/I2 led to the only formation of the pyrrolidine products in 84−99% yield via 5-exo radical cyclization. The vinylic halogen substitution not only successfully inhibits the competing ionic iodocyclization process to allow the radical cyclization to proceed smoothly but also shows a remarkable effect in controlling the regioselectivity of cyclization.

Control of the regioselectivity of sulfonamidyl radical cyclization by vinylic halogen substitution.

Atom transfer radical cyclization reactions of N-(4-pentenyl)iodoacetamides were investigated. The reactions were efficiently promoted by BF3·OEt2. For N-alkenyl-substituted iodoamides, excellent regioselectivity in favor of 8-endo cyclization was observed, while both 7-exo and 8-endo cyclization products were formed with the 8-endo cyclization preferred in the cases of N-(2-allylphenyl)-substituted iodoamides. Density functional theory calculations at the B3LYP/6-31G* level revealed that both the s-trans and the s-cis conformational transition structures were feasible for the 8-endo cyclization of N-alkenyl-substituted α-carbamoyl radicals while 7-exo transition structures were much less stable. For the cyclization of N-(2-allylphenyl)-substituted α-carbamoyl radicals, the transition structures for 8-endo and 7-exo cyclizations were of comparable energy. These results were in excellent agreement with the experimental observations.

8-endo versus 7-exo cyclization of alpha-carbamoyl radicals. A combination of experimental and theoretical studies.

Background/aims To improve the accuracy of pterygium screening and detection through smartphones, we established a fusion training model by blending a large number of slit-lamp image data with a small proportion of smartphone data. Method Two datasets were used, a slit-lamp image dataset containing 20 987 images and a smartphone-based image dataset containing 1094 images. The RFRC (Faster RCNN based on ResNet101) model for the detection model. The SRU-Net (U-Net based on SE-ResNeXt50) for the segmentation models. The open-cv algorithm measured the width, length and area of pterygium in the cornea. Results The detection model (trained by slit-lamp images) obtained the mean accuracy of 95.24%. The fusion segmentation model (trained by smartphone and slit-lamp images) achieved a microaverage F1 score of 0.8981, sensitivity of 0.8709, specificity of 0.9668 and area under the curve (AUC) of 0.9295. Compared with the same group of patients’ smartphone and slit-lamp images, the fusion model performance in smartphone-based images (F1 score of 0.9313, sensitivity of 0.9360, specificity of 0.9613, AUC of 0.9426, accuracy of 92.38%) is close to the model (trained by slit-lamp images) in slit-lamp images (F1 score of 0.9448, sensitivity of 0.9165, specificity of 0.9689, AUC of 0.9569 and accuracy of 94.29%). Conclusion Our fusion model method got high pterygium detection and grading accuracy in insufficient smartphone data, and its performance is comparable to experienced ophthalmologists and works well in different smartphone brands.

/pdf/accurate-detection-and-grading-of-pterygium-through-299lrgt2.pdf

Accurate detection and grading of pterygium through smartphone by a fusion training model

The coordination of Cr(CO)3 to chlorobenzenes significantly reduces the C-Cl bond dissociation energy. Treatment of chloroarene-Cr(CO)3 complexes with SmI2/HMPA at room temperature led to complete dechlorination. Reaction of o-allyloxychlorobenzene-Cr(CO)3 complexes with SmI2 at room temperature resulted in the corresponding dechlorinative cyclization products in good to excellent yields. Competition experiments indicated the following relative reactivities of dehalogenation by SmI2: PhI/PhCl-Cr(CO)3/PhBr/PhCl = 50:1:0.3:<0.001. On the other hand, the coordination of Mn(CO)3(+) to chlorobenzene showed a much smaller activation effect. Density functional theory calculations revealed that the spin delocalization effect of the metal center plays an important role in the C-Cl bond activation.

Effect of M(CO)3 (M = Cr, Mn+) on aromatic C-Cl BDE in (eta6-ArCl)M(CO)3 complexes.

Aim: Vascular endothelial function and atherosclerosis are known to be important risk factors for cardiovascular disease. However, it remains unknown whether remnant cholesterol (RC) correlates with vascular endothelial function and atherosclerosis as represented by flow-mediated vasodilation (FMD) and brachial-ankle pulse wave velocity (baPWV). Therefore, in this study, we aimed to investigate this in the general population. Methods: In this study, we examined 13,237 subjects who have undergone blood lipid, FMD, and baPWV measurements. Participants were divided into four groups based on RC quartiles. Multivariable linear regression models were used to calculate odds ratios for FMD and baPWV according to the RC levels. Results: A significant negative relationship was found between RC and FMD (β=−0.14,p=0.014), whereas RC was positively associated with baPWV (β=21.42,p＜0.001), especially in the male and without chronic disease medication populations. The population was divided into three groups according to their lipids: dyslipidemia group, nondyslipidemia but RC increased group (RC ＞0.78 mmol/L), and nondyslipidemia and RC normal group (RC ≤ 0.78 mmol/L). The FMD of the three groups was 7.09%±3.36%, 7.39%±3.38%, and 7.57%±3.54%, respectively. The baPWV of the three groups was 1445.26±261.56 cm/s, 1425.04±265.24 cm/s, and 1382.73±267.75 cm/s. Significant differences were noted between the groups. Conclusions: The findings indicated that a higher RC was an independent predictive factor for participants with endothelial function and atherosclerosis. It is important to use RC as a risk management indicator of vascular function, especially for those with normal conventional lipid parameters but increased RC.

/pdf/the-association-of-remnant-cholesterol-with-endothelial-3vwnlfe3.pdf

The Association of Remnant Cholesterol with Endothelial Dysfunction and Subclinical Atherosclerosis in a Check-Up Population in China

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Papers

8-endo versus 7-exo cyclization of alpha-carbamoyl radicals. A combination of experimental and theoretical studies.

Accurate detection and grading of pterygium through smartphone by a fusion training model

Effect of M(CO)3 (M = Cr, Mn+) on aromatic C-Cl BDE in (eta6-ArCl)M(CO)3 complexes.

The Association of Remnant Cholesterol with Endothelial Dysfunction and Subclinical Atherosclerosis in a Check-Up Population in China