Callimorphine

Absolute configuration of the creatonotines and callimorphines, two classes of arctiid-specific pyrrolizidine alkaloids.[Pubmed:17175448]

Insect Biochem Mol Biol. 2007 Jan;37(1):80-9.

Arctiids which as larvae sequester pyrrolizidine alkaloids (PAs) from their food plants are known to synthesize insect-specific PAs by esterifying necine bases derived from plant PAs with necic acids of insect origin. There are two classes of insect PAs, the creatonotines and the Callimorphines. The creatonotines contain as necic acids either 2-hydroxy-3-methylbutyric acid (creatonotine A) or 2-hydroxy-3-methylpentanoic acid (creatonotine B). The three known Callimorphines contain 2-hydroxy-2-methylbutanoic acid whose hydroxyl group can be either free (deacetylCallimorphine) or acetylated (Callimorphine) or propionylated (homoCallimorphine). Insect PAs are assumed to play an important role in the recycling of plant derived necine bases and the processing by trans-esterification of PA monoesters that cannot be directly transmitted to the insect's pupal and adult life-stages. The absolute configuration of the insect-specific necic acids was elucidated in the context of the suggested role of the insect PAs as insect-made mimics of plant monoester PAs of the lycopsamine type. For this purpose all needed stereoisomers were synthesized and a gas chromatography-mass spectrometry (GC-MS) method was established that allows the enantioselective separation and assignment of the stereochemistry of all insect specific necic acids as their methyl esters. The method could also be applied to the GC-MS analysis of the intact alkaloids which were hydrolyzed during injection and converted into their methyl esters. Analysis of the creatonotines and Callimorphines isolated from the polyphagous arctiids Estigmene acrea and Grammia geneura that were fed with pure PAs and defined PA mixtures revealed the following absolute configuration: the Callimorphines and creatonotine A were present in 2'R configuration, whereas creatonotine B was found as mixture of (2'R, 3'S)- and (2'S, 3'S)-stereoisomers. The ratio of 2'S to 2'R was extremely variable ranging from 98% S to 94% R. The cause of the lack of stereospecificity is discussed particularly in respect of a possible epimerization of the hydroxyl group at C-2' in analogy to the known epimerization at C-3' of plant acquired PAs of the lycopsamine type.

Structure-activity relationships of pyrrolizidine alkaloids in insect chemical defense against the orb-weaving spider Nephila clavipes.[Pubmed:12035917]

J Chem Ecol. 2002 Apr;28(4):657-68.

Pyrrolizidine alkaloids (PAs) are known to protect Arctiidae moths and Danainae and Ithomiinae butterflies against the orb-weaving spider Nephila clavipes (Araneae, Araneidae, Tetragnathinae), which liberates adults of these insects unharmed from its web. We tested against this spider the role of eight PAs and one derived structure [an 89:11 mixture of the 12-membered macrocyclic diester free base integerrimine and senecionine and the respective N-oxide; two hydrolysis products from this mixture (the necine base retronecine, its respective N-oxide, and a mixture of integerriminic and senecionic necic acids); the 12-membered macrocyclic senkirkine; the 9-O-monoester free base senecioylretronecine and its respective N-oxide; and the 9-O-monoester free base Callimorphine (a PA biosynthesized only by insects from retronecine)]. The mixture integerrimine-senecionine N-oxide seems to be more active than the respective free base [LibD50 (liberation dose 50) = 0.042 and 0.153 microg/dry weight of prey, respectively], but the difference in activity between the N-oxide and free base of the 9-O-monoester senecioylretronecine was slight (LibD50 = 0.167 and 0.104, respectively). Senkirkine, an otonecine base PA that does not form N-oxide and is not found in insects, was the less active, showing the highest LibD50 (0.354). The difference in antipredator activity between N-oxides and free bases from macrocyclic diesters and monoesters may be correlated with physicochemical properties of these molecules in interaction with the Nephila receptors. For the active structures, there was a significant correlation between dosage and antipredator activity. Both forms of retronecine and a necic acid mixture were inactive, supporting the hypothesis that PAs biosynthesized by insects from retronecine were originally produced and stored in order to optimize chemical defense. Comparison of dose/activity data with reported amounts of PAs in butterflies suggested that, in general, PA-specialist insects are protected against predation by Nephila.

Pyrrolizidine alkaloids in the arctiid mothHyalurga syma.[Pubmed:24249009]

J Chem Ecol. 1993 Apr;19(4):669-79.

The arctiid mothHyalurga syma (subfamily Pericopinae) sequesters pyrrolizidine alkaloids (PAs) from its larval food plantHeliotropium transalpinum (Boraginaceae). Colorimetric quantification of total PAs in the larvae, pupae, and adults ofHyalurga revealed mean values of about 286-445mug per individual (1.4-2.6% of dry weight). The PA mixtures found in the moth and its larval food plant were evaluated by GC-MS. Food-piant leaves were found to contain the diastereoisomeric retronecine esters indicine (IIIa), intermedine (IIIb), and lycopsamine (IIIc), and the heliotridine ester rinderine (IIId) only as minor constituents, whereas 3'-acetylrinderine (IVc) (68% of total PAs) and the respective 3'-acetyl esters of indicine (IVa) and intermedine (IVb) (both 17%) were the major alkaloids. Supinine (IIa) is detectable in traces only. The PA mixtures in eggs, larvae, pupae, and imagines ofHyalurga were identical: indicine, intermedine, and lycopsamine accompanied by considerable amounts of supinine and amabiline or coromandalinine (IIb/IIc) were the major components. Only larvae were found to store small quantities of a 3'-acetyl derivative. Rinderine and its 3'-acetyl ester were never found in the insects. Low concentrations of the arctiidspecific PA Callimorphine (I) were present in larvae, pupae, and imagines. The differences in the PA patterns of the insects and their larval food plant suggest thatHyalurga is capable of modifying plant-derived PAs by inversion of the 7-OH configuration (conversion of the necine base heliotridine into retronecine), and perhaps the inversion of the 3'-OH [conversion of (+)-trachelanthic acid into (-)-viridifloric acid], although the possibility of a selective sequestration of the respective retronecine esters cannot be excluded. Some trials with the orb-weaving spiderNephila clavipes, a common neotropical predator, showed that both freshly emerged and field-caught adults ofHyalurga syma are liberated unharmed by the spider. The liberation could be related to the presence of PAs in the moths.