Indolizidine alkaloids configuration

Swainsonine is a trihydroxylated bicyclic indolizidine alkaloid with four chiral centres, whose relative stereochemistry was determined by X-ray crystallographic analysis and the absolute configuration was deduced on the basis of biosynthetic and asymmetric induction studies, and then confirmed by an enantiospecific synthesis from D-mannose [2a]. 

Juliprosopine from Prosopis juliflora A. DC. is a new type of indolizidine alkaloid, and on the basis of an extensive spectroscopic and chemical study it has been assigned the structure (2), in which relative configurations are shown for the substituents on the piperidine ring. Juliprosopine may be derived biosynthetically from combination of a dihydropyrrole unit with two Prosopis piperidine alkaloids that have C12 side-chains.2... 

Synthesis and absolute configuration of (+)-lentiginosine, indolizidine alkaloid, a potent and selective inhibitor of amyloglucosidase 07EJO1551. Total synthesis of antitumor pyrroloiminoquinone alkaloids discorhab-dins and makaluvamines 05COC1567. 

The 5,6,8-trisubstituted indolizidine alkaloids form another class of amphibian skin alkaloids that has grown enormously since the first member of this group was reported in 1997. At present approximately 70 such alkaloids have been tentatively or positively identified.As has so often happened with minor or trace components of the skin extracts, very few of them have been characterized completely, and the relative configurations are almost entirely unknown other than for a few in which strong or weak Bohlmann bands in the FTIR spectra imply cis- or iram-relationships respectively between the hydrogen atoms on C-5 and C-8a. 

The structural features of the solanum alkaloids are based on two primary skeletal configurations solanidane, with or without glycoside functionalities, as featured by the toxic and teratogenic steroidal alkaloids a-chaconine and a-solanine with the indolizidine type E-F ring (Figure 2.7a) and the spirosolane... 

The alio series of the pumiliotoxin A class have an additional hydroxyl group that has been placed at C-7 on the indolizidine ring, without assignment of configuration. Three members of the alio series have been assigned the tentative structures (7), (8), and (9).3 Pumiliotoxins A and B are relatively toxic, and comparable in potency to strychnine. Pumiliotoxin B has a potent cardiotonic and myotonic activity.3 An enantioselective total synthesis of pumiliotoxin A alkaloids from L-proline has already been announced.4... 

A recent NMR analysis of the stereoisomeric oxindole alkaloid models 36 and 37 as well as indolizidine reveals that chemical shifts of the piperidine portion of these bases are interpretable only in terms of a trans configuration of the indolizidine ring system and that the chemical shift values of C-3 and C-9 are strong diagnostic indicators of the configuration at C-7. This is borne out by assignment of S values of rhynchophylline and isorhynchophylline (Table VIII) (12). 

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