Alangium alkaloids

Another class of alkaloids recently synthesized by Tietze and coworkers using a three-component domino Knoevenagel/hetero-Diels-Alder reaction included the Ipecacuanha alkaloids such as emetine (2-798) [402], and the Alangium alkaloids such as tubulosine (2-799) [403]. Both types belong to the group of tetrahydroi-soquinoline alkaloids, and are formed in Nature from dopamine and the monoter-... 

For the next few pages Ipecac alkaloids, f Alangium alkaloids, New structure, Revised or established structure, II Newly isolated structure. 

Chiral syntheses of benzo[a]quinolizidine-type Alangium alkaloids 88H(27)1009. 

As regards the 21 benzo[a]quinolizidine-type Alangium alkaloids, they can be structurally classified into four types according to their substitution patterns in the aromatic ring A (i) 9,10-dimethoxy type (72), (ii) 8-hydroxy-9,10-dimethoxy type (73), (iii) 9-hydroxy-lO-methoxy type (74), and (iv) 10-hydroxy-9-methoxy type (75) 7,10,16). Thus, type 72 includes 10 alkaloids... 

A full account was also given (53) of their preliminary work (1,81, 82) on the racemic and chiral syntheses and structure establishment of alangicine (25). The NMR spectra of ( )-24 (103) and ( )-25 (53) confirmed the correctness of the endocyclic double bond structure in the dihydroisoquinoline moiety of the two Alangium alkaloids, (-I- )-9-demethyl-psychotrine (24) and (-l-)-alangicine (25). 

The alternative structure 23 (i.e., 127 or 128) has still to be assigned to the Alangium alkaloid (-)-demethylcephaeline ). Fujii and Ohba 108) revealed a detailed account of their preliminary work 1,109) on the syntheses of (-)-9-demethylcephaeline (127) and (-)-lO-demethylcephaeline (128). Unfortunately, however, a sample of natural (-)-demethylcephaeline for a direct comparison remains unavailable, precluding identification of either 127 or 128 with this Alangium alkaloid. 

Formula 175 represents the incorrect planar structure proposed by Brindley and Pyman 147) in 1927 for emetine (1). In this connection, Harada et al. 148) synthesized the four stereoisomers possible for ( )-C-noremetine Pyman [( )-176] and isolated them in the form of hydrobromide salts. Takacs and Boito 149) synthesized the (-)-tricyclic alcohol 177, a one-carbon homolog of the Alangium alkaloid (-)-protoemetinol (34), from the chiral formamidine 117 in 36% overall yield via a five-step route proceeding through the stereoselective iron-catalyzed cyclization of the key intermediate 178. 

Scheme 1. Biosynthesis of ipecac and Alangium alkaloids nitrogenous portion. Pathway (a) in Cephaelis ipecacuanha pathway (b) in A. lamarckii.

Agrimonolide, Y2 Agroclavine, K17 Ajaconine, K32 Ajmalicine, K9-10 Ajmaline, Kll Akuammicine, K12 Akuammidine, Kll Akuammine, K12 Alangidiol, T45 Alangium alkaloids, K2 Alanine, A1 Alaninol, A19... 

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