Alkaloids pentacyclic

The (TMSlsSiH-mediated radical cyclization has been applied in the formation of ring C in two pentacyclic alkaloids (Reactions 55 and After... 

Alstonamine (11) - a pentacyclic alkaloid with a hydrogenated azocino[4,3-l7]-indole fragment - has been isolated from the leaves of this plant (87P2139). 

A different approach to the derivation of Strychnos-type pentacyclic alkaloids has been used (85T2557). Photocyclization of N-chloroacetyl derivative 99 takes place in position 4 of the indole core (but not in position 2, as expected) to form 100 (Scheme 27). 

Lew Mander of the Australian National University recently reported (J. Am. Chem. Soc. 2003. /25, 2400) the total synthesis of the pentacyclic alkaloid GB I3 3, which had been isolated from the bark of the rain forest tree Galbulimima belgraveana. In the course of the synthesis, he took full advantage of benzene precursors, while at the same time carefully establishing each of the eight stereogenic centers of... 

Fused tetracyclic and pentacyclic alkaloids constitute a relatively new class of natural products isolated mostly from ascidians and sponges. Cytotoxic, antimicrobial and antiviral activities have been reported for many of these compounds. The manzamine alkaloids, Fig. (33) are characterized by a complex pentacyclic diamine linked to C-l of P-carboline moiety. Manzamine have been isolated mainly from six different genera of marine sponges Haliclona, Pellina, Xestospongia, Ircinia, Pachypellin and Amphimedon. 

Camptothecin (CPT, Cl) is a potent antitumor pentacyclic alkaloid isolated from Camptotheca acuminata Decne. (Nyssaceae family) and originating in China (36, 37). Interest in CPT was sparked by the discovery that its primary cellular target is DNA topo I (38). 10-Hydroxycamptothecin (C2), which also occurs naturally, has a better therapeutic index and is used in China for treating many cancers. 

A novel pentacyclic alkaloid, citrinadin A 48, was isolated from the culture broth of the fungus Penicillium citrinum, which was isolated from a marine red alga. 48 exhibited cytotoxicity against murine leukemia L1210 and human epidermoid carcinoma KB cells (IC50 6.2 and 10 pg mL", respectively). The absolute stereochemistry of citrinadin A was determined. 

The total synthesis of pentacyclic alkaloid (-)-haliclonadiamine was accomplished by D.F. Taber and co-workers. The Noyori asymmetric hydrogenation was used to prepare a bicyclic 3-hydroxy ester intermediate in enantiopure form from a racemic bicyclic P-keto ester via kinetic resolution. It was found that the hydrogenation only took place in the presence of added HCI and by optimizing the amount of HCI added, the proportion of the total reduced ketone could be controlled. About 87% of the "matched" ketone was reduced, while the other P-keto ester enantiomer was not significantly converted to the reduced product. Interestingly, the diastereoselectivity of the hydrogenation depended on the nature of the added acid with HCI, the trans diastereomer was the major product, while with AcOH the cis diastereomer was dominant. 

A pentacyclic alkaloid, so far unnamed, isolated (90) from the leaves of Voacanga africana Stapf, is the epoxide 75 of a degraded aspidospermane base in which C-5 and C-6 of the original tryptamine ethanamine chain have been lost this is the first recorded occurrence of this ring system. 

This ring system can be seen in the pentacyclic alkaloids ascididemin 28, 2-bromoleptoclinidone 29, 11-hydroxyascididemin 30, 8,9-dihydro-ll-hydroxyascididemin 31, calliactine 32, the heptacyclic eilatin 33, and the octacyclic biemnadin 34. (See Section II,D,1 on pyrido[2,3,4-/c/]acridines.)... 

Besides dehydrolycopecurine (37) two other pentacyclic alkaloids, inundatine (38 CigH23N02) and isoinundatine (39 CieH23N02) are present among the alkaloids of Lycopodium inundatum (5). The structures of both were established by relating them to alopecurine (29) of known structure 10). 

The Weinreb group has also applied intramolecular imino Diels-Alder chemistry to the synthesis of the phenanthroindolizidine antitumor alkaloid tylophorine (42) (Scheme 2-XIV).85 86 In this example, a diene incorporated into a phenanthrene unit proved sufficiently reactive in an intramolecular cyclization to provide the pentacyclic alkaloid ring system. A similar strategy was later used to synthesize the phenanthroquinolizidine alkaloid cryptopleurine.89... 

Cat s claw (Uncaria tomentosa and Uncaria guianensis), an herbal medicine from the Amazon, is widely used to treat inflammatory disorders. Both species of cat s claw provide effective antioxidant and anti-inflammatory activities, but Uncaria guianensis is the more potent of the two. Non-alkaloid fractions from both species have been found to decrease lipopolysaccharide (LPS)-induced TNF-a and nitrite production in RAW 264.7 cells, and oral pretreatment for 3 days with Uncaria tomentosa actually prevented TNFa mRNA expression and apoptosis. Interestingly, the pharmacological properties of these species do not seem to be dependent on the presence of oxindole or pentacyclic alkaloids [191]. 

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