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Regulation of the interconversion of the phosphorylated and nonphosphorylated forms of pyruvate dehydrogenase in rat adipose tissue by insulin48-50 and in rat heart, liver, and kidney by long-chain fatty acids51 has been reported. Insulin apparently increases the proportion of the nonphosphorylated form of pyruvate dehydrogenase, and this effect is antagonized by adrenaline and by adrenocorticotrop-(50) S.

Summary. The carbon shifts of the Iboga-type alkaloids catharanthine, voacanginc, coronaridine, ibogaine, dihydrocatharanthine and epiibogamine were recorded and correlated with the conformation of the natural bases. A 13C-NMR. analysis of heyneaninc determined its C(19) configuration and a similar study of cpihcyneanine proved its structure.In connection with problems of structure determination and synthesis of indole alkaloids of the Iboga type it became of importance to apply 13C-NMR. spectroscopy thereto. As a consequence the following study of a select group of such natural products was undertaken and isoquinuclidine (l), its N-methyl derivative (2), some monosubstituted bicyclo[2.2.2joctanes (3) and two bicyclo[2.2.2]octenes (4) used as models. The carbon shifts of the first two models are depicted on formulas 1 4 ) and 2 and those of bicycles 3 5 ) and 46) listed in Table 1. The total of the y-effects on C(l) and C(3) is 7.7 ppm greater for the hydroxy group of 3c than the methyl group of 3b, relative to 3a. The comparable magnitude of the y-effect of the two groups as a result of fixed gauche, non-bonded interactions [3] [4] and thc shielding of ycarbons by hydroxy groups truns anti-periplanar to them within rigid six-membered rings [j] suggest that the excess shielding by the hydroxy group of 3c is an acyclic equivalent of the lattcr phcnomenon. This result indicates that caution must be cxerciscd in the assessment of shielding contributions to y carbon atoms from oxygen in all staggered, acyclic conformations.The introduction of a double bond into the strained bicyclo[2.2.2]octane skeleton leads to stronger deshielding of the allylic carbons and a decrease of the cndocyclic homoallyl effect relative to the shift differences of cyclohexenes and cyclohexanes [2] [6] (cf. also the 6b + 5a change).

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