Tetrahydronicotinic acid

The other alkaloids derived from nicotinic acid, with pyridine nucleus such as arecoline, arecaidine and guvacoline, are tetrahydronicotinic acid (guvacine) derivatives. 

Tetrahydronicotinic acid 86 Tetrahydroprotoberbirines 152 Tetrahydrorhombifoline 31 Tetrandrine 7, 35, 45 Tetrodotoxin 9, 43 Thebaine 7, 35 Thebanine 21, 136... 

Nicotinic acid undoubtedly provides the basic skeleton for some other alkaloids. Ricinine (Figure 6.35) is a 2-pyridone structure and contains a nitrile grouping, probably formed by dehydration of a nicotinamide derivative. This alkaloid is a toxic constituent of castor oil seeds (Ricinus communis Euphorbiaceae), though the toxicity of the seeds results mainly from the polypeptide ricin (see page 434). Arecoline (Figure 6.36) is found in Betel nuts (Areca catechu Palmae/Arecaceae) and is a tetrahydronicotinic acid derivative. Betel nuts are chewed in India and Asia for the stimulant effect of arecoline. 

Seeds of Areca catechu (betel nut) (Palmae) contain the simple jV-methyltetrahydropyridine 3-carboxylic acid (jV-methyl-A -tetrahydronicotinic acid) arecaidine and arecoline (arecai-dine methyl ester) (Section 1, Appendix) that are mACh-R agonists and accordingly parasympathetic stimulants. Betel nut also yields guvacine (A -tetrahydronicotinic acid) that is an anti-epileptic GABA transport inhibitor. Conversely the jV-methyl dihydropyridone derivative ricinine from seeds of Ricinus communis (castor seed) (Euphorbiaceae) is a stimulatory agonist acting at the benzodiazepine site of the GABA(A) receptor. 

Arecoline (N - Methyl - A - tetrahydronicotinic acid meOiyl ester, methyl ester of arecaidine)... 

SYNS ARECAIDINE METHYL ESTER ARECOLINE BASE METHYL-1,2,5,6-TETRA-HYDRO-l-METHYL-NICOTINATE N-METHYL-A-TETRAHYDRONICOTIN-IC ACID METHYL ESTER N-METHYLTETRAHYDRO-PYRIDINE-P-CARBO-XYLIC ACID METHYL ESTER 1,2,5,6-TETRA-HYDRO-l-METHYLNICOTINIC ACID, METHYL ESTER... 

The most striking examples for the positive confinement effect of supports on enantioselectivity have been provided by Thomas and Johnson s research group [13, 14, 16], who demonstrated that even nonenantioselective catalysts can show significant asymmetric induction when anchored onto a suitable support. The Pd catalyst 14 covalently supported within the pores of MCM-41 affected the hydrogenation of ethyl 1,4,5,6-tetrahydronicotinate (16) to afford nipecotic acid ethyl ester (17) at 17% ee (turnover number (TON) = 291), whereas the use of 15, the... 

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