Carbon-13 n.m.r. spectroscopy

Specific applications of carbon-13 n.m.r. spectroscopy to the glycophorins, an important family of glycoproteins present in the human erythrocyte membrane, are discussed by K. Dill (Clemson), who demonstrates the value of C-n.m.r. spectra for the structural mapping of glycoproteins. 

A more detailed treatment of carbon-13 n.m.r. spectroscopy, and the interp tation of spectroscopic data for many of the synthesised compounds. 

Carbon-13 n.m.r. spectroscopy has been used to study benzylisoquinoline and tetrahydroisoquinoline alkaloids and their JV-methyl quaternary salts.30 N-Benzylpapaverinium bromide has been shown to undergo aerial oxidation in alkaline solution to 2-benzyl-6,7-dimethoxyisoquinolone and to give bases of general structure (10) with methylamine, benzylamine, and pyrrolidine.31 Chlorosulphonation of papaverinol affords the sulphonic acid ester (11), mild hydrolysis of which yields the acid (12), which with diazomethane is esterified and dehydrated to (13).32 N-Methyl-l,2-dihydropapaverine has been shown by kinetic studies and orbital-symmetry requirements to rearrange to the salt (14) by the route previously postulated.33... 

Carbon-13 N.M.R. Spectroscopy.—A study of the, 3C n.m.r. spectra of twenty-five hemiterpenoid quinoline alkaloids and related prenylquinolines, including C-, 0-, and A-prenyl-quinoline and -quinolone derivatives, hydroxyisopropyldihydro-furoquinolinones, hydroxydimethyldihydropyranoquinolinones, and furoquino-lines, has been carried out 6 only isolated examples were reported previously.7,8... 

Carbon-13 N.M.R. Spectroscopy.—The 13C n.m.r. spectra of ten 4-quinazolinones have been reported, and are useful for determining their predominant tautomeric forms and for resolving controversial structural problems.13 Thus, the resonance of C-4 in compound (22), containing a double-bond between C-2 and N-3, appears at ca 1 p.p.m. to lower field (167.7-168.9 p.p.m.) than in compound (23), in which there is a double-bond between N-l and C-2. There is also a significant difference between resonances of C-8a in the two groups of compounds, those in compounds... 

Penta- and Hexa-aza-compounds. 3,6-Dibenzyl-l,2,4,5-tetrazine (811) undergoes a complex reaction with methanolic potassium hydroxide, giving 3-benzyl-7-methoxy-6-phenylimidazo[l,2-6][l,2,4,5]tetrazine (812), whose structure has been elucidated by X-ray analysis.Carbon-13 n.m.r. spectroscopy has been used to investigate azido-tetrazole valence tautomerism for the systems (813) and (814)" and for (815) (816) (817)." ... 

The effect of the nature and size of 2-substituents on the preferred conformation of 1,3-dioxepans has been studied by i.r. and dipole-moment measurements.Carbon-13 n.m.r. spectroscopy provides a useful way to distinguish between ring sizes 5—7 of cyclic acetals, using both the chemical shift of the acetal carbon and the coupling constant with its attached proton. ... 

Carbon-13 n.m.r. spectroscopy has been shown to be a useful technique for distinguishing between stereoisomers of spirobenzylisoquinolines. A review of the synthesis and biosynthesis of alkaloids of this group has been published. Methods of synthesis from tetrahydroberberines have been described above. The dihydroxy-base (125 R = = H) has been converted into yenhusomidine (125 ... 

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