1. Controlled Synthesis of Polyphosphazenes with Chain-Capping Agents
Krzysztof Matyjaszewski, Robert A Montague Molecules. 2021 Jan 10;26(2):322. doi: 10.3390/molecules26020322.
N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by 1H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation.
2. Shear Stress and VE-Cadherin
Vincenza Caolo, Hanna M Peacock, Bahar Kasaai, Geertje Swennen, Emma Gordon, Lena Claesson-Welsh, Mark J Post, Peter Verhamme, Elizabeth A V Jones Arterioscler Thromb Vasc Biol. 2018 Sep;38(9):2174-2183. doi: 10.1161/ATVBAHA.118.310823.
Objective- Vascular fusion represents an important mechanism of vessel enlargement during development; however, its significance in postnatal vessel enlargement is still unknown. During fusion, 2 adjoining vessels merge to share 1 larger lumen. The aim of this research was to identify the molecular mechanism responsible for vascular fusion. Approach and Results- We previously showed that both low shear stress and DAPT ( N-[ N-(3,5-difluorophenacetyl)-L-alanyl]- S-phenylglycine t-butyl ester) treatment in the embryo result in a hyperfused vascular plexus and that increasing shear stress levels could prevent DAPT-induced fusion. We, therefore, investigated vascular endothelial-cadherin (VEC) phosphorylation because this is a common downstream target of low shear stress and DAPT treatment. VEC phosphorylation increases after DAPT treatment and decreased shear stress. The increased phosphorylation occurred independent of the cleavage of the Notch intracellular domain. Increasing shear stress rescues hyperfusion by DAPT treatment by causing the association of the phosphatase vascular endothelial-protein tyrosine phosphatase with VEC, counteracting VEC phosphorylation. Finally, Src (proto-oncogene tyrosine-protein kinase Src) inhibition prevents VEC phosphorylation in endothelial cells and can rescue hyperfusion induced by low shear stress and DAPT treatment. Moesin, a VEC target that was previously reported to mediate endothelial cell rearrangement during lumenization, relocalizes to cell membranes in vascular beds undergoing hyperfusion. Conclusions- This study provides the first evidence that VEC phosphorylation, induced by DAPT treatment and low shear stress, is involved in the process of fusion during vascular remodeling.
3. Total Synthesis of (+)-Trachyspic Acid 19- n- Butyl Ester
Alex A Rafaniello, Mark A Rizzacasa Org Lett. 2020 Mar 6;22(5):1972-1975. doi: 10.1021/acs.orglett.0c00319. Epub 2020 Feb 17.
The first total synthesis of the alkyl citrate trachyspic acid 19-n-butyl ester (1) is described. A formal [2 + 2]-cycloaddition of the silylketene acetal derived from lactone 6 with di-n-butylacetylene dicarboxylate 7 provided the cyclobutene diester 5 with a dr >20:1. Acid-mediated rearrangement of 5 followed by lactone ring-opening and ester protecting group manipulation eventually provided orthogonally protected aldehyde 3. A Nozaki-Hiyama-Kishi coupling between 3 and vinyl iodide 4 followed by oxidation of the resultant allylic alcohol gave enone 16, which was converted into the triester 17 (dr 6:1) by a spirocyclization/oxidative cleavage/elimination sequence. Removal of the t-butyl esters then afforded trachyspic acid 19-n-butyl ester (1).
