Annonaceae alkaloids

Annonaceae alkaloids occurrence and a compilation of their biological activities, 74, 233... 

In Chapter 5, Emidio Vasconcelos Leitao Da Cunha and coworkers have summarized in an enormous effort the occurrence and the biological activities of the Annonaceae alkaloids. This article represents a valuable and very useful lexical compendium for everybody who is working in this field of... 

The pseudobenzylisoquinoline alkaloids are fairly widespread in nature, being found among members of Berberidaceae, Annonaceae, Fumariaceae, and Ranunculaceae. The biogenesis of the pseudobenzylisoquinoline alkaloids assumes their formation from protoberberinium salts by C-8—C-8a bond scission in a Baeyer-Villiger-type oxidative rearrangement to produce the enamides of type 73 and 74. These amides may be further biotransformed either to rugosinone (76) type alkaloids by hydrolytic N-deformylation followed by oxidation or to ledecorine (75) by enzymatic reduction. These transformations were corroborated by in vitro studies (80-82). It is suggested that enamide seco alkaloids may be precursors of aporphine alkaloids (80), on one hand, and of cularine alkaloids (77), on the other. 

A list of the secobisbenzylisoquinoline alkaloids with their species of origin is included in Table VIII. The secobisbenzylisoquinoline alkaloids have mainly been found among members of the family Berberidaceae, less frequently in the Annonaceae, and in only a single case in the Ranunculaceae. In Table IX some of the physical data and spectral features of secobisbenzylisoquinoline alkaloids are presented. 

Taxonomically close to the Annonaceae, the Lauraceae family abounds with apor-phinoid alkaloids. A remarkable advance in the search for topoisomerase inhibitors from Lauraceae has been provided by Woo et al. (6). Using DNA-unwinding assay and structural modeling, they showed that dicentrine can attain a relatively planar conformation and molecular bulk which allow it to occupy the active site of topoisomerase II which becomes inactive. The requirement of a suboptimal conformation to achieve DNA binding appears to make dicentrine less potent against topoisomerase II than the... 

Whereas the Annonaceae are characterized primarily by benzylisoquinoline alkaloids, two pyrrolidine alkaloids have recently been found in species belonging to this family. Squamolone (29) was isolated from Annona squamosa L. by Chinese workers in 1962 (68). Despite careful spectroscopic investigation and a total synthesis (Eq. 1), squamolone was assigned the incorrect diazepine formula 30. The correct structural formula (29) was later established by an unambiguous synthesis of 30 (Eq. 2). Compounds 29 and 30 proved to have very similar spectroscopic properties, which could justify the early confusion (69). 

Guatteria megalophylla Diels (Annonaceae) afforded (/ ,/ )- , 0-dimethylcur-ine (144), C38H42N206, mp 133-136°C (EtOAc-cyclohexane), identified by UV, NMR, MS, and ORD, and by comparison with a sample synthesized by CH2N2 methylation of (/ ,/ )-l2 -0-methyIcurme (145, Section II,C,64), also isolated from this plant (82). (/ ,/ )-< ,0,-Dimethylcurine had been prepared by methylation of (/ ,/ )-curine (75) (83), but was not previously reported in nature however, (5,S)-0,0-dimethylcurine is a known alkaloid of Cissampelos pareira (84). 

The title alkaloids (218 and 218a, respectively) were obtained in very small amounts from Polyalthia nitidissima (Annonaceae) as an inseparable mixture,... 

An abstract stating preliminary results of an investigation of the Colombian plant, Pseudoxandra lucida (Annonaceae), has appeared. The new bases oxandrine (251) and pseudoxandrine (252) were isolated and characterized by spectroscopic means. These alkaloids are the first keto biphenyl-linked bases and are possible intermediates in the biogenesis of seco biphenyl alkaloids 126). Details on these and two related alkaloids have recently been published 126a). 

Secantioquine (512), C37H3gN2Og, amorphous, [a]D —15° (c 1, CHC13), was obtained from Pseudoxandra aff. lucida (Annonaceae). The structure was deduced from the UV base shift, NMR, and formation of secantioquine 0,O-diacetate by oxidation (KMn04/Me2CO) of the 0,0-diacetyl derivative of antioquine (466). Secantioquine is the first biphenyl-linked seco bisbenzyltetrahydroisoquinoline alkaloid (551,568). 

Alkaloid Y, isolated from the bark of Schefferomitra subaequalis (Annonaceae), has now been shown to correspond to the known aristolactam BII (cepharanone-B) (72).51... 

It is interesting to note that the occurrence of C-7 oxygenated aporphine alkaloids with the C-6a R configuration is limited to the families Annonaceae, Lauraceae, Magnoliaceae, and Menispermaceae. Aporphine alkaloids oxygenated at both C-4 and C-7 have been found in the Annonaceae, but (-)-stephadiolamine /3-A-oxide (48) is the first known alkaloid hydroxyl-ated at both C-4 and C-7 and having a cis relationship between H-6a and H-7. (-)-O-Acetylsukhodianine is the first known example of a naturally occurring 7-acetoxylated aporphine (30). 

Aporphinoids are by far the most abundant alkaloids in this genus and also, generally speaking, in the family Annonaceae. Guatteria has proved to be a rich source of unusual structures of this general type. Aporphines have been reviewed in Volume 24 of this treatise (3) and elsewhere (4-7), and a review on aporphinoids of the Annonaceae has just been published (8). For this reason we address the structures and chemistry of only a few alkaloids of this type that have not been included in the Kametani and Honda review (5). 

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