Barton esters structure

Vogel and coworkers have described the synthesis of anti-1,6 7,12-/ wmethano[ 14]annulene 44 for studies of its -electron structure.32 Incorporation of AIBN into decarboxylative bromination of vinylogous carboxylic acid 45 via Barton esters increased the efficiency of this reaction, Scheme 16b. Harvey... 

Structure and Reactivity PTOC Esters Related Thiohydroxamate Systems Preparation of Barton Esters 67-1... 

Such artificial photonucleases can be generated by UV excitation of N-hydroxypyridinethiones (N-HTP) 1 and 6 (R = H) and N-aroyloxypyridine-2-thiones (1, R = ArCOj), which can photocleave DNA through release of hydroxyl or aryloyloxyl radicals, repectively. " " Some more complex structures based on Barton esters were also prepared. Recent efforts are focused on combining these highly efficient DNA-cleaving families with an intercalative moiety (Scheme 20). ... 

There is quite some evidence for a mechanism as formulated above,especially for the six-membered transition state—the Barton reaction is observed only with starting materials of appropriate structure and geometry, while the photolysis of nitrite esters in general seldom leads to useful products formed by fragmentation, disproportionation or unselective intermolecular hydrogen abstraction. 

Backbone (protein), 1028 Backside displacement. reaction and.363-364 von Baeyer, Adolf, 113 Baeyer strain theory, 113-114 Bakelile, structure of, 1218 Banana, esters in, 808 Barton, Derek, H. R., 389 Basal metabolic rate, 1169 Basal metabolism. 1169-1170 Base, Bronsted-Lowry, 49 Lewis, 57, 59-60 organic, 56-57 strengths of, 50-52 Base pair (DNA), 1103-1105 electrostatic potential maps of. 

Piperidine 141 was synthesized from the Barton-McCombie reaction <75JCSP11574> of 142 which gave the expected amido-ester (96 %) as a 3 2-mixture of diastereomers. The mixture was hydrolyzed to the corresponding carboxylic acid which, upon thermal decarboxylation, gave the desired /V-bcnzyl lactam (85% overall yield) as a single diastereomer whose structure was unequivocally established by a single-crystal X-ray analysis. Reduction of the lactam with LiAlH4 (81%) followed by debenzylation via... 

The Barton reaction was utilized during the synthesis of various terpenes and has played a crucial role in the elucidation of terpene structures. The Barton nitrite ester reaction was a key step in E.J. Corey s synthesis of azadiradione and perhydrohistrionicotoxin . Even though the yields were low, other ways to access the same intermediates would have been tedious, and afforded lower overall yields than in the applied Barton reactions. 

This approach was also used for phosphine oxides [256] and has been already extended, in the last few years, to other structures such as other hydroxyalkyl ketones [257], [4-(methylthio) phenyl]-2-morpholinopropanone [258], Barton s esters [66], sulfonyl ketones [250], and so on. 

Next, alcohol 35 was transformed into 36 by reductive dehydroxylation via the nonisolated intermediate xanthate. Hydrolysis of the ester group in 35 to form 30 was followed by decarboxylation to generate 37 by using an improved Barton s method employed with HOTT (5-(l-oxido-2-pyr-idinyl) 1,1,3,3-tetramethylthiouronium hexafluorophos-phate) [35]. Treatment of 37 with TBAF furnished alcohol, which was converted into the proposed structure of paesslerin A by using scandium-catalyzed acetylation. Unfortunately, comparisons of the H- and C-NMR data of the synthetic compound with those reported for the natural product revealed that the substances are not identical. The 2D-NMR data for synthetic 29 are fiiUy consistent with the structure of the target. The result clearly demonstrates that a revision of the structure of natural paesslerin A is required (Scheme 4.17). 

The nuclease requires Ca + ions for activity, with no other divalent metal ion being able to support catalysis. A large number of other phospodiester-ases have been found to be dependent on divalent metal ions for activity, including the restriction endonuclease icoRI (Barton et al, 1982). Thus elucidation of the mechanism of the reaction catalyzed by staphylococcal nuclease may provide important clues to the mechanisms of the other metal-dependent phosphodiesterases. Fortunately, staphylococcal nuclease will catalyze, albeit at a low rate, the hydrolysis of a number of mononucleotide esters (Cuatrecasas et al., 1969), including thymidine 5 -(4-nitro-phenyl phosphate) this ester is hydrolyzed to thymidine and 4-nitrophenyl phosphate. We have determined the stereochemical course of the hydrolysis of thymidine 5 -(4-nitrophenyl [ 0, 0]phosphate) and interpreted the result in terms of the structure of the active site of the enzyme. 

---