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Amphibians 5,8-disubstituted indolizidine alkaloids

Fig. 8. Recently synthesized 3,S-disubstituted indolizidine alkaloids fiom amphibians. Fig. 8. Recently synthesized 3,S-disubstituted indolizidine alkaloids fiom amphibians.
The 5,8-disubstituted indolizidines and 1,4-disubstituted quinolizidines are the more common structural patterns found in amphibian skin[21]. None of these alkaloids has so far been reported from any other source. In addition, the biological activity of only a few 5,8-disubstituted indolizidines has been investigated due to the isolation in minute quantities from the skin. Among them, the relative stereochemistry of quinolizidine 2071 was anticipated to be 75 by our chiral synthesis of 76[35] followed by stereocontrolled synthesis of 75[36]. A sample of synthetic racemate of 75 had produced the best separations on GC analysis with (3-dextrin chiral column[36]. [Pg.444]

The amphibian alkaloids considered to be 3,5-disubstituted indolizidines are tabulated below. Two other bicyclic alkaloids, proposed as monosub-stituted indolizidines in an earlier review, are included. These are 167B, which was considered likely to be a 5-n-propylindolizidine, based on its mass spectrum and biosynthetic considerations, and 209D, which was considered likely to be a 5-n-hexylindolizidine. These two indolizidines have been synthesized (130,131), but efforts to compare the synthetic indolizidines to natural 167B and 209D were thwarted when the natural trace alkaloids could no longer be detected in extracts. Structures of relatively well-characterized 3,5-disubstituted indolizidines from amphibians are shown in Fig. 11. [Pg.229]

Disubstituted indolizidines, unlike many classes of amphibian alkaloids, are not unique to amphibians. 3,5-Disubstituted indolizidines such as monomorine I [(5Z,9Z)-195B] occur in ants of the genera Monomorium and Solenopsis (125,129,134). Some of the ant indolizidines are as follows (5Z,9Z)-3-n-butyl-5-methylindolizidine (monomorine I), (5Z,9Z)-3- -ethyl-5-methylindolizidine, (5Z,9Z)-3-hexyl-5-methylindolizidine, and (5 ,9Z)-3-butyl-5-(4-pentenyl)indolizidine. A series of 5-substituted indolizidines, the piclavines, were reported recently from a marine tunicate (Clavelina picta) (135). [Pg.232]

Indolizidine and quinolizidine alkaloids found in amphibians and ants were studied by Daly and co-workers who classified them in two different classes, A and B, Fig. (1) [2,15-17]. The former include 3,5- and 5,8-disubstituted indolizidines, 5,6,8-trisubstituted indolizidines and 1,4- and 4,6-disubstituted quinolizidines that can be derived from straight-chain carbon precursors. The latter contain one or more isoprene units, and include pumiliotoxins (PTX-A), allopumiliotoxins (a//o-PTX-A or... [Pg.234]

By incorporating a chiral auxiliary, (+ )-rrans-2-(a-cumyl)cyclohexyl (TCC), into pyridinium salt 688, Comins and co-workers were assured of excellent asymmetric induction in a divergent synthesis of three 5,8-disubstituted amphibian indolizidine alkaloids (Scheme 93) (467,499). Addition of but-3-enylmagnesium bromide to 688 yielded the dlhydropyridone 689 as a single diastereomer in 91% yield after recrystallization. After a series of functional group manipulations, the C-8 methyl group was introduced stereoselectively by enolate alkylation (690 -> 691),... [Pg.199]

In their comprehensive 2005 survey of amphibian alkaloids, Daly and colleagues reported that about 80 5,8-disubstituted indolizidines had been fuUy or tentatively characterized at that stage, making it the largest class of alka-... [Pg.344]


See other pages where Amphibians 5,8-disubstituted indolizidine alkaloids is mentioned: [Pg.188]    [Pg.195]    [Pg.197]    [Pg.201]    [Pg.188]    [Pg.197]    [Pg.96]    [Pg.231]    [Pg.239]    [Pg.246]    [Pg.165]    [Pg.246]    [Pg.165]    [Pg.315]    [Pg.326]    [Pg.362]    [Pg.382]   
See also in sourсe #XX -- [ Pg.187 , Pg.188 , Pg.189 , Pg.190 , Pg.191 , Pg.192 ]

See also in sourсe #XX -- [ Pg.187 , Pg.188 , Pg.189 , Pg.190 , Pg.191 , Pg.192 ]




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