Quinolizidine alkaloid

Quinohzidine alkaloids Quinolizidine Cytisine Lupanine Sparteine... 

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

This group of alkaloids has a pyridone nucleus and generally takes the tetracyclic or tricyclic form. The a for pyridone alkaloids is L-lysine, while the j8, q> and X the same as for other quinolizidine alkaloids. Quinolizidine alkaloids containing the pyridone nucleus are the P from the (—/-sparteine by cleavage of the C4 unit. The first quinolizidine alkaloid with the pyridone nucleus is tricyclic cytisine, which converts to four cyclic alkaloids. In this synthesis the anagyrine, the most poisonous quinolizidine alkaloid with a pyridone nucleus, has its own synthesis pathway. 

In 1967, Fujita et al. (5,6) isolated three piperidine metacyclophane alkaloids (type B) from Lythrum anceps Makino. The third structural variant of the Lythraceae alkaloids, quinolizidine metacyclophane (type C), was... 

Piperidine alkaloids Quinolizidine alkaloids Indolizidine alkaloids... 

Piperidino alkaloids Pteridine alkaloids Pyrrolidinone alkaloids Pyrroli/idine alkaloids Quinolizidine alkaloids Sosqriilorpono alkaloids Steroidal alkaloids Triterpene alkak rids Tn rpano alkaloids ... 

Human Poisoning by Pyrrolizidine Alkaloids Medicinal Uses of Pyrrolizidine Alkaloids Quinolizidine Alkaloids Biosynthesis... 

Complex Quinolizidine Alkaloids Systematic Usefulness of Quinolizidine Alkaloids Biological Activity of Quinolizidine Alkaloids Medicinal Uses of Quinolizidine Alkaloids Quinolizidine Alkaloids and Livestock Poisoning Mescal—Hallucinogenic Properties of Quinolizidine Alkaloids... 

Quinolizidine alkaloids are derived from lysine and have two fused 6-membered rings that share a nitrogen atom. In contrast to the pyrrolizidine alkaloids, quinolizidine alkaloids usually occur free. At least 570 quinolizidine alkaloids are known (Verpoorte et al., 1991). 

Alkaloids allelopathy endophytes pyrrolizidine alkaloids quinolizidine alkaloids... 

The reaction of 2-(a-pyridyl)alkylmalonic acid with J -piperideine leading to formation of 3-((x-pyridyl)quinolizidine-l-carboxylic acid on decarboxylation, has been used by Van Tamelen and Foltz (316) for the syntheis of the alkaloid lupanine (Scheme 20). A very elegant synthesis of matrine has been accomplished by Bohlmann et al. (317). 

Tetrahydropyridines 103 undergo a Michael reaction to afford [ran.s-(2,3)-cis-(2,6)-trisubstituted piperidines 104 (97T9553). The reaction is stereoselective (a single stereoisomer was obtained) and provides a convenient route to the 5,8-disubstituted indolizidine 105 and 1,4-disubstituted quinolizidine system 106 (found in Dendrobates alkaloids) by introduction of various alkyl, alkenyl, or... 

The synthetic utility of radical cyclization was used as the key step in a four-step synthesis of the natural product (d,0-epilupinine (134b, a quinolizidine alkaloid) (75CB1043) from methyl nicotinate (146). Thus, l-(4-bromobutyl)-3-methoxycarbonyl-l,4,5,6-tetrahydropyridine (140), obtained from methyl nicotinate (146), was cyclized to 141 (43%), which on reduction with LiAlH4 in THF provided 134b in 95% yield (89T5269). 

Conformational study of geissoschizine isomers and their model compounds (geissoschizine is the indolo[2,3-fl]quinolizidine derivative considered to be an important participant of indole alkaloids biogenesis) 99H(51)649. 

Racemic and chiral syntheses of some indolo[2,3-<2]quinolizidine alkaloids through a lactim ether route 98H(47)525. 

The utility of lOOC reactions in the synthesis of fused rings containing a bridgehead N atom such as pyrrolizidines, indolizidines, and quinolizidines which occur widely in a number of alkaloids has been demonstrated [64]. Substrates 242 a-d, that possess properly positioned aldoxime and alkene functions, were prepared from proline or pipecolinic acid 240 (Eq. 27). Esterification of 240 and introduction of unsaturation on N by AT-alkylation produced 241 which was followed by conversion of the carbethoxy function to an aldoxime 242. lOOC reaction of 242 led to stereoselective formation of various tricyclic systems 243. This versatile method thus allows attachment of various unsaturated side chains that can serve for generation of functionalized five- or six-membered (possibly even larger) rings. 

Molecular mechanics (MM) calculations have been employed for determining dihedral angles and to establish a comparison with values calculated from coupling constants, during conformational studies of tricyclic and tetracyclic quinolizidine alkaloids. The MM results had to be treated with care, as they sometimes predicted ring conformations different to those supported by experimental data <1999JST215>. 

Cytisine is a tricyclic quinolizidine alkaloid that binds with high affinity and specificity to nicotinic acetylcholine receptors. In principle, this compound can exist in several conformations, but semi-empirical calculations at the AM 1 and PM3 levels have shown that stmctures 19 and 20 are more stable than other possible conformers by more than 50 kcalmol-1. Both structures differ by 3.7 kcalmol 1 at the AMI level and 2.0 kcalmol 1 at the PM3 level, although this difference is much smaller when ab initio calculations are employed <2001PJC1483>. This conclusion is in agreement with infrared (IR) studies and with H NMR data obtained in CDCI3 solution, which are compatible with an exo-endo equilibrium < 1987JP21159>, although in the solid state cytisine has an exo NH proton (stmcture 19) (see Section 12.01.3.4.2). 

The combination of H NMR, 13C NMR data and H- H and H- C correlations has been widely employed for the structural assignment of quinolizidine natural products. One example is the alkaloid senepodine A 30,... 

Mass spectral data have also been employed for biological studies aimed at determining the distribution of quinolizidine alkaloids within a plant. For instance, the analysis of stem sections of Lupinus polyphyllus and Cytisus scoparius by laser desorption mass spectrometry led to the conclusion that these alkaloids are restricted to the epidermis and probably also to the neighboring one or two subepidermal cell layers <1984MI230>. 

Two-dimensional thin-layer chromatography (TLC) with adsorbent gradient has allowed the separation of quinolizidine alkaloids in the herb and in several alkaloids from Genista sp. <2004MI89>. 

Quinolizine alkaloids, including sophocarpine, matrine and sophoridine have been determined by GC-MS techniques in kuhuang, a traditional Chinese medicine (GC = gas chromatography) <2005MI967>. Similarly, GC-MS has allowed a phytochemical study of the quinolizidine alkaloids of Genista tenera <2005MI264>. 

The high-performance liquid chromatography (HPLC) determination of quinolizidine alkaloids in Radix Sophora flavescens was assisted by using tris(2,2 -bipyridyl)ruthenium(n) electrochemoluminescence <2004MI237>. Tandem HPLC-MS techniques have allowed the development of a sensitive and specific method for the determination of sophocarpine, matrine, and sophoridine in rabbit plasma <2005MI1595>. 

A similar procedure was applied to the synthesis of quinazolidine 189 from precursor 188 in the total synthesis of the natural product known as ( )-quinolizidine 2071 190, an alkaloid isolated from the skin of the Madagascar mantelline frog Mantella baroni, that shows an exceptional axial stereochemistry for the ethyl group at C-l. Quinolizidine 189 was transformed into 190 by oxidation and two consecutive Wittig methylenations (Scheme 34) <1999CC2281>. 

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