Iodine scission

Iodine scission of phosphorothioate containing RNA for probing phosphates... 

Only the head-to-tail adducts were obtained in the [2+2] photoaddition of 4-hydroxy-l-phenyl[l,8]naphthyridin-2(l//)-one with various alkenes in methanol (Scheme 3). The photolysis of the hypoiodites generated by the in situ reaction of the cycloadducts with excess mercury(ll) oxide-iodine reagent in benzene induced a regioselective scission of the non-ring junction bond of the alkoxyl radical to give substituted 3,9-dihydro-9-phenylyfuro[2,3- ][l,8]naphthyridin-4(2//)-one and/or 3,5-dihydro-5-phenylfuro[3,2-f][l,8]naphthyridin-4-(2//)-ones <1996T6125>. 

Photolysis of iodine. Unlike DBK, molecular iodine photodissociates via a one bond scission. Also the wavelength of the laser pulse used by Otto et al. (19) results in a relatively mild, low energy separation of the photogenerated radicals. Therefore 12 photodissociation should be a more sensitive probe for the characterization of solvent cage effects. 

AJthaugh various propiisals for the ni chani m of methanol homologation exist, the course of the reaction is still not fully understood. This is especially true for the activation of methanol with a concomitant C-0 bond scission. Also, the folc of the iodine promoter and of ligands remains unclear. This situation is controversial to the closely-related carbonylation of methanol to acetic acid with rhodium catalysts, where the oxidative addition of the intermediate methyl iodide to a rhodium (1) is a generally-accepted reaction path [SR]. 

Another common method for determination of alpha-samylase involves measurement of the diminution of the iodine-stainability of whole starch or amylopectin )8-limit dextrin. These methods are useful, as very small quantities of alpha-amylase may be estimated in this way. They are comparative, and cannot be used to determine rates of bond scission, unless they are carefully calibrated by a method that measures reducing end-groups. Such a calibration has been made for the action of hog-pancreas alpha-amylase on waxy-maize starch, although the validity of the reducing-power determinations, made with iodine and thiosulfate, has been confirmed for maltose only thus, it is not yet known whether the calibration is actually valid for the experimental system in which larger oligomers, for example, the triose and tetraose, are also formed. 

Irradiation of benzobicyclooctadienol (467) in benzene containing HgO and iodine gives a benzobicyclooctadienone (468) (equation 158). Its formation involves a rearrangement of an 8-membered C-centred radical generated by )5-scission of an alkoxy radical (equation 158) °. ... 

In structural studies, a low concentration of iodine is advisable in order to obtain a structure-dependent modification pattern. In footprinting of proteins on RNA the optimal conditions should permit reaction with all the free phophorothioates (i.e. those not interacting with the protein). Since iodine also reacts strongly with proteins the quantitative strand scission may be limited by the dissociation of the protein-RNA complex. 

Regioselective 8-scission of the a-oxoalkyloxyl radical derived from the hypoiodlte (144) is involved, for example, in the formation of the novel a-hydroxy-e-lactones (145) and (146) on irradiation of the steroidal alcohol in the presence of mercury(II) oxide and iodine. 

The value of Gtotalgas was found to be 0.87 [385]. Methane and hydrogen are the main products [386, 387]. A new absorption at 11.25 pm, assigned to vinylidene double bonds, was observed [386]. Total unsaturation was measured by titration with iodine monochloride. It corresponds to the formation of 1.87 double bonds per main-chain scission irrespective of temperature. Main-chain scissions were determined at various temperatures (Table 28). An Arrhenius-type plot of Gscission versus temperature gives an activation energy of 2.5 kcal mole-1 above 0°C. Below 0°C, the temperature coefficient is negligible. 

It was possible to racemize bulbocapnine 0-methyl ether and 0-benzoyl-bulbocapnine by first oxidizing with iodine and subsequently reducing with zinc in dilute acid. The dZ-O-methyl ether melted at 136° and was resolvable into the I- and d-derivatives ([a] d 247° in chloroform) by means of d- and Z-tartaric acid, respectively. Hydrolysis of the dZ-O-benzoylbulbo-capnine (m.p. 201-202°) with sodium methylate yielded dZ-bulbocapnine (m.p. 209-210°). As in other aporphines, it was possible to effect scission of the nitrogen ring in bulbocapnine by treatment with benzoyl chloride at its boiling point. 

Hypoiodite-type reaction. Treatment of the allylic alcohol 1 with QHsI (OAc)2 and iodine generates an alkyloxy radical, which undergoes -scission to a followed by cyclization to a cis-hydroazulenone ring system (2). The CH2I group of 2 can be reduced to a methyl group by a catalytic amount of BusSnH (60% yield). Treatment of 2... 

The photolysis of the hypoiodite generated from a cyclobutanol derived from the [2-1-2]-photoaddition of 4-hydroxy-1(2H)-isoquinolinone with an electron-deficient alkene in the presence of mercury(ll) oxide and iodine resulted in a (3-scission at the ring-fusion bond of the cyclobutanoxyl radical to give a 3,6-epoxybenzazocinone derivative in 76% yield (Scheme 75). A weaker aromatic stabilization and destabilization by the cyano substituent in the carbon-centered radical arising from a fragmentation at the non-fusion bond led to ring expansion. 

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