Lactones, from oxidation

Gramicidin A, however, is attacked by JV -bromoacetamide (NBA) and N-bromosuccinimide (NBS) (Gross and Witkop, unpublished observation). In 50 % aqueous ethyl alcohol at room temperature 5 % of the peptide bonds (20% of the tryptophyl peptide bonds) are cleaved with NBS. Methyl alcohol must be avoided because it opens the spirodioxindole lactone from oxidized tryptophan to the ester even at room temperature. The cleavage mixture separates on electrophoresis (pH = 2.5, sodium-formate buffer) into four ninhydrin-positive components of which the fastest migrating one was identified as ethanolamine. Dinitrophenylation showed leucine and alanine to be additional NHs-terminals of the released fragments. 

Kim EJ, Hye KJ, Yong KK, et al. Suppression by a sesquiterpene lactone from Carpe-sium divaricatum of inducible nitric oxide synthase by inhibiting nuclear factor-KB activation. Biochem Pharmacol 2001 61 903-910. 

Hasan CM, Mia MY, Rashid MA, Connolly JD. 5-Acetoxyisogoniothalamin oxide, an epoxystyryl lactone from Goniothalamus sesquipedalis. Phytochemistry 1994 37 1763-1744. 

Starting from 5-O-acetyl-1,2-0-isopropylidene-a-D-glucofuran-urono-6,3-lactone, Kinoshita and coworkers178 achieved the synthesis of 3-amino-3-deoxy-l,2-0-isopropylidene-a-D-allofuranuronic acid by the following sequence of reactions methanolysis of the lactone ring, oxidation at C-3 to form methyl 5-0-acetyl-l,2-0-isopropyli-dene-a-D-riho-3-hexulofuranuronate, followed by stereospecific reduction of the oxime of the latter. 

Optically Active Lactones from Metal-Catalyzed Baeyer-Villiger-Type Oxidations Using Molecular Oxygen as the Oxidant... 

D-glucose and its lactone from 2,3,6-trimethyl-D-glucose provided conclusive proof that the ring system was not of the hexylene oxide type.142 188 The final evidence necessary to characterize the tetramethylglucose in question as a furanose derivative was provided by Haworth, Hirst and Miller,176 who demonstrated that oxidation of the tetramethylglucose with bromine water and of the resulting lactone with nitric acid yielded dimethoxysuccinic acid and oxalic acid, but not i-zyZo-trimethoxyglutaric acid, the absence of which ruled out a pyranose structure. 

It should be noted that nonmetallic redox reactions also experience the sonication influence. The preparation of y lactons from olefines by oxidation of manganese triacetate is an example. 

Silyloxypropanols (314) derived from lactones undergo oxidative ring expansion to afford higher homologous o ,/3-unsaturated lactones (316) (90TL197). The reaction proceeds through the fluoride ion assisted formation of intermediate 315, which on reductive elimination of F " species yields the product (Scheme 80). 

An efficient method for preparing aldono-1,4-lactones (y-aldonolactones) as the single products from oxidation of unprotected or partially protected monosaccharides was reported [9]. It consisted in treatment of the latter by catalytic amounts of [RuH2(PPh3)4], in the presence of an excess of benzalacetone (frans-4-phenylbut-3-en-2-one) as the hydrogen acceptor, in DMF. The corresponding y-lactones were... 

Oxidation of oleic acid to 10-hydroxyoctadecanoic acid by a gram-positive bacterium was described with a transformation yield of 65% at a concentration of 50 g oleic acid after 72 h in a medium containing Tween 80 [232]. The hydroxy fatty acid can be converted to 4-dodecanolide, an important coconut-fruity like lactone, by -oxidation with yeasts, affording a total lactone yield of about 20% from oleic acid [222, 232]. 

The key steps in the ring expansion of the cyclobutanones (186) and (787) are the Baeyer-Villiger oxidation effected by H202—HOAc. It is noteworthy to point out that the Baeyer-Villiger oxidation is regiospecific and serves to be an excellent method for the preparation of y-lactone from cyclobutanones. 

A brief review of procedures for asymmetric metal-catalyzed Baeyer-Villiger oxidations is given with asymmetric copper-catalyzed synthesis of 3-phenyl-2-oxepanone as representative of the enantioselective synthesis of lactones from cyclic ketones . 

It should be noted that nonmetallic redox reactions also experience the sonication influence. The preparation of y-lactons from olefines upon manganese triacetate oxidation is an example. The reaction with monomethyl malonate in acetic acid, which does not occur at 0-10°C, proceeds smoothly when sonication is applied (Allegretti et al. 1993). From cyclohexene, only the cis ring fusion in the bicyclic lactone is observed the product is formed at 80% yield for 15 min at 10°C. The overall scheme of the reaction, without the detailed mechanism is shown in Scheme 8-18. 

The enzymatic Baeyer-Villiger oxidation enantioselective synthesis of lactones from mesomeric cyclohexanones, J. Am. Chem. Soc. 1988, 110, 6892-6893. 

I. Isaac, I. Stasik, D. Beaupere, and R. Uzan, A new and direct access to glycono-1,4-lactones from glycopyranoses by regioselective oxidation and subsequent ring restriction, Tetrahedron. Lett., 36 (1995) 383-386. 

N. Pravdic and H. G. Fletcher, Jr., The oxidation of 2-acetamido-2-deoxyaldoses with aqueous bromine, Two diastereomeric 2-acetamido-2,3-dideoxyhex-2-enono-l,4-lactones from 2-acetamido-2-deoxy-D-glucose, -mannose, and -galactose, Carbohydr. Res., 19 (1971) 339-352. 

Finally, two tetrahydrofurofuran lignans (the stereoisomers asarinin and sesamin, Scheme 12) have been subjected to MTO-catalyzed oxidation. In both cases, the major product originates from oxidative cleavage of one of the phenyl-tetrahydrofuran bonds yielding a lactone. In a CH2Cl2/MeCN mixture using UHP as the oxidant, 65% conversion and 87% selectivity for the lactone is obtained. With immobilized MTO/PVP-2% as catalyst in CH2Cl2/EtOH, similar results are obtained [95]. 

The oxidative radical cyclization of o-alkyl and o-arylbenzoic acids by BTI and iodine, photochemically, was a good way to prepare y- and 5-lactones from these acids. The experimental conditions were similar to those mentioned in the previous Section but milder, since no heating was required and the amount of iodine was 0.1 equiv. in respect to BTI. In the following example, a small amount of an iodinated 5-lactone was also formed [70] ... 

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