Piperidines alkaloids

New synthetic methodology on the route to asymmetric piperidine alkaloids 99JHC1549. 

Hyperaspine (1), a perhydropyrido[l,2-c][l,3]oxazine alkaloid was isolated from the ladybird beetle H. campestris (01TL4621). 9-Epi-6-epipinidinol (90), a piperidine alkaloid, was prepared from a perhydropyrido[l,2-c][l,3]oxazin-l-one derivative (98T13505). Perhydropyrido[l,2-c][l,3]oxa-zin-l-ones were used to prepare 2,6-disubstituted piperidines (96CJC2434). 

As an application of this method1S, the preparation of enantiomerically pure piperidine alkaloids ( )-(i )-coniine (3 steps, 72% overall yield) and (-)-(2i ,6S)-dihydropinidine (6) from 5 is described. For related works, see refs 16, 19-29 and literature cited therein. 

Aliphatic nitriles (—CH2CH2CH2CH2CN) (m/z 82, 96, 110, 124, 138, 152, etc., suggest straight-chain nitriles) Benzoquinones Piperidine alkaloids Some fluoroalcohols... 

RRM of enantiopure cyclopentene 382, induced by commercially available catalyst C, was the key step in Blechert s total synthesis of the bis-piperidine alkaloid (+)-astrophylline (384) [159]. Exposure of metathesis precursor 382 to only 1 mol% C provided within 2 h bicycle 383 in 82% yield (Scheme 75). 

Blechert s synthesis of the piperidine alkaloid (-)-halosaline (387) by Ru-catalyzed RRM is outlined in Scheme 76 [160]. In the presence of 5 mol% of catalyst A, the ring rearrangement of metathesis precursor 385 proceeded cleanly with formation of both heterocyclic rings in 386. In situ deprotection of the cyclic silyl ether in 386, followed by selective reduction and removal of the to-syl group led to 387. 

The utility of strained disubstituted cycloheptenes in alkaloid syntheses is highlighted by Blechert s total syntheses of the bis-pyrrolidine alkaloid (+)-dihydrocuscohydrine (390) [161],thebis-piperidine alkaloid (-)-anaferin (in the form of its dihydrochloride 393) [162], and indolizine 167B (397) [163] (Scheme 77). 

Felpin, F.X., Girard, S., Vo-Thanh, G., Robins, R.f, ViUieras, L, Lebreton, L (2001) Efficient Enantiomeric Synthesis of PyrroUdine and Piperidine Alkaloids from Tobacco. Journal of Organic Chemistry, 66, 6305-6312. 

An excellent example of a RCM/ROM domino process is shown in the total synthesis of the piperidine alkaloid (-)-halosaline (6/3-19) by Blechert and coworkers (Scheme 6/3.3) [231]. The key step is the reaction of the enantiopure cyclopentene derivative 6/3-17 to give 6/3-18 with 5 mol% of the catalyst 6/3-13. Further transformations of 6/3-18 led to the natural product 6/3-19. 

Besides piperidine alkaloids, a total of 19 pyrrolidines have been found in the secretions of thief ants and fire ants of the genera Solenopsis and Monomorium. Among these, compounds 80-84 are simple pyrrolidines with two saturated linear all-carbon side chains only in Solenopsis latinode is there a secondary amine (82) and its methylated analog (85). One or two terminal unsaturations are present in compounds 86-91, which all possess a (hex-l-en)-6-yl chain and a 5-, 7-, or 9-carbon saturated chain. Compounds 93, 94, 96, 97, and 98 are the A-l-pyrrolines corresponding to pyrrolidines 80, 82, 90 (93 and 96 corresponding to 80, 94 to 82, and 97 and 98 to 90). 

The chemistry of pepper has long been studied and the pungent principle of black pepper—a piperidine alkaloid, piperine 134—was isolated as early as 1877 (201). Its synthesis from the acid and piperidine was accomplished in 1882. (202). The corresponding pyrrolidine alkaloid trichostachyne (135) was isolated some 100 years later from several Piper species (see below). The cooccurence of piperidine and pyrrolidine alkaloids is a common feature of the chemistry of pepper. In many cases, the crude alkaloid extract is first cleaved with acids or bases and then each alkaloid is reconstituted by selective amidation. For the sake of unity, this chapter will be limited to comments on pyrrolidines, even in cases where they are minor alkaloids. 

The total syntheses of these pepper alkaloids are not those of pyrrolidines but rather syntheses of their acid parts. Thus dihydrowisanidine (137) has been prepared by a series of reactions, the key step of which is the formation of the carbon-carbon double bond by a Wittig-Homer reaction (217, 218). Schemes 41 and 42 summarize two syntheses of okolasine from sesamolmethyl ether (279) of course, routes to okolasine also yield the corresponding piperidine alkaloid wisanine. Molybdenum-catalyzed elimination of allylic acetate (149) yielded (E,E)-diene ester 150 en route to trichonine (220) worthy of note is the use of an aluminum amide in the preparation of amide 143 from ester 150 (Scheme 43). 

Strategies based on two consecutive specific reactions or the so-called "tandem methodologies" very useful for the synthesis of polycyclic compounds. Classical examples of such a strategy are the "Robinson annulation" which involves the "tandem Michael/aldol condensation" [32] and the "tandem cyclobutene electrocyclic opening/Diels-Alder addition" [33] so useful in the synthesis of steroids. To cite a few new methodologies developed more recently we may refer to the stereoselective "tandem Mannich/Michael reaction" for the synthesis of piperidine alkaloids [34], the "tandem cycloaddition/radical cyclisation" [35] which allows a quick assembly of a variety of ring systems in a completely intramolecular manner or the "tandem anionic cyclisation approach" of polycarbocyclic compounds [36]. 

Figure 2.2 Three piperidine alkaloid teratogens from Conium maculatum (poison-hemlock) (a) coniine, (b) y-coniceine, and (c) A-methyl coniine, with accompanying LD50 as determined in a mouse bioassay.

Nicotiana species and certain lupine species also contain potent toxic and teratogenic piperidine alkaloids (Figure 2.4). All teratogenic piperidine alkaloids have specific structural characteristics that are responsible for induction of birth defects. Their molecular structures include a piperidine ring, with a side chain of at least three carbons or larger attached adjacent to... 

In addition to lupines, poison-hemlock and Nicotiana spp., other plant species of the genera Genista, Prosopis, Lobelia, Cytisus, Sophora, Pinus, Punica, Duboisia, Sedum, Withania, Carica, Hydrangea, Dichroa, Cassia, Ammondendron, Liparia, and Colidium contain potentially toxic and teratogenic piperidine alkaloids. Many plant species or varieties from these genera may be included in animal and human diets (Keeler and Crowe, 1984). 

Fodor, G.B. and Colasanti, B. (1985). The pyridine and piperidine alkaloids chemistry and pharmacology, in Pelletier S., Ed., Alkaloids chemical and biological perspectives, Vol. 3, John Wiley and Sons, New York, pp. 3-91. 

Keeler, R.F. and Panter, K.E. (1989). Piperidine alkaloid composition and relation to crooked calf disease-inducing potential of Lupinus formosus. Teratology, 40, 423-432. 

Panter, K.E., Bunch, T.D., Keeler, R.F., Sisson, D.V. and Callan, R.J. (1990). Multiple congenital contractures (MCC). and cleft palate induced in goats by ingestion of piperidine alkaloid-containing plants Reduction in fetal movement as the probable cause, Clin. Toxicol., 28, 69-83. 

Panter, K.E., Gardner, D.R. and Molyneux, R.J. (1998a). Teratogenic and fetotoxic effects of two piperidine alkaloid-containing lupines L. formosus and L. arbustus) in cows, J. Nat. Toxins, 1, 131-140. 

The reactions depicted in Scheme 39 were already conducted in view of a potential use in the synthesis of pyrrolidinols and piperidinols. The structural feature of a 2-arylmethyl-3-hydroxysubstitution is not only found in preussin but also in anisomycin (152) [87] or in the piperidine alkaloid FR 901483 (153) [88] (Fig. 5). 

A new piperidine alkaloid Adalinine 352 was prepared in racemic form, using a rearrangement as a key step (equation 134). Enolate chemistry allowed double a-alkylation of cyclopentanone, producing 350 after oxime formation. Rearrangement provided a clear conversion into the lactam 351, easily converted to racemic Adalinine 352. 

During the synthesis of 436, Muraoka and colleagues produced the diazobi-cyclo[4.3.1]decane 435 via the classical ring expansion (equation 184). Huisgen-White rearrangement of the cyclic lactam leads to 436, a key synthetic intermediate for piperidine alkaloids. 

M. Yagi, T. Kouno, Y. Aoyagi, and H. Murai, The structure of moranoline, a piperidine alkaloid from Morns species, Nippon Nogei Kagaku Kaishi, 50 (1976) 571-572. 

L-lysine Piperidine alkaloids Piperidine Anaferine Lohelanine Lohehne A-methyl pelletierine Pelletierine Piperidine Piperine Pseudopelletierine Sedamine... 

L-methionine L-phenylalanine Phenylalanine-derived alkaloids Piperidine alkaloids Quinolizidine alkaloids Indolizidine alkaloids True alkaloids... 

Alkaloid biosynthesis needs the substrate. Substrates are derivatives of the secondary metabolism building blocks the acetyl coenzyme A (acetyl-CoA), shikimic acid, mevalonic acid and 1-deoxyxylulose 5-phosphate (Figure 21). The synthesis of alkaloids starts from the acetate, shikimate, mevalonate and deoxyxylulose pathways. The acetyl coenzyme A pathway (acetate pathway) is the source of some alkaloids and their precursors (e.g., piperidine alkaloids or anthraniUc acid as aromatized CoA ester (antraniloyl-CoA)). Shikimic acid is a product of the glycolytic and pentose phosphate pathways, a construction facilitated by parts of phosphoenolpyruvate and erythrose 4-phosphate (Figure 21). The shikimic acid pathway is the source of such alkaloids as quinazoline, quinoline and acridine. 

The synthesis pathway of quinolizidine alkaloids is based on lysine conversion by enzymatic activity to cadaverine in exactly the same way as in the case of piperidine alkaloids. Certainly, in the relatively rich literature which attempts to explain quinolizidine alkaloid synthesis °, there are different experimental variants of this conversion. According to new experimental data, the conversion is achieved by coenzyme PLP (pyridoxal phosphate) activity, when the lysine is CO2 reduced. From cadeverine, via the activity of the diamine oxidase, Schiff base formation and four minor reactions (Aldol-type reaction, hydrolysis of imine to aldehyde/amine, oxidative reaction and again Schiff base formation), the pathway is divided into two directions. The subway synthesizes (—)-lupinine by two reductive steps, and the main synthesis stream goes via the Schiff base formation and coupling to the compound substrate, from which again the synthetic pathway divides to form (+)-lupanine synthesis and (—)-sparteine synthesis. From (—)-sparteine, the route by conversion to (+)-cytisine synthesis is open (Figure 51). Cytisine is an alkaloid with the pyridone nucleus. 

---