Iridodial

The paired defensive gland reservoirs of Staphylininae are situated between tergites 8/9 and may be everted upon molestation. Therefore, the secretion acts topically. The chemistry varies considerably between species. While Staphylin-ina use terpenoids as solvents for, e.g. iridodial 17, representatives of Philonthina produce a lot of acetates and hydrocarbons as solvents for actinidin 60 [8,118]. 

Representatives of Xantholininae possess an unpaired nonreversible anal gland reservoir at their abdominal tip. As already reported, the secretion contains iridodial, actinidin, terpenoid aldehydes, ketones, limonene, and isopule-gol [8,118]. 

Defensive Compounds. In Cerambycinae, paired metasternal glands are situated in the thorax, while associated reservoirs open near the hind coxae [8]. Rose oxide 190 (Scheme 21) and iridodial 17 were identified from Aromia moschata... 

GC-EAD analysis of thoracic extracts of the male green lacewing, Chrysopa nigricornis Burmeister, showed that two compounds elicited response from conspecific male antennae 1-tridecene and (li , 25, 5R, 8i )-iridodial. Iri-dodial also attracted males of the goldeneyed lacewing, C oculata Say, and to a lesser extent, C. coloradensis Banks males. 

Natural (—)-actinidine (9a) is prepared from nepetalinic acid imide (262) via dichloropyridine (263) 403) and from iridodial (264) via bis (2,4-dinitrophe-nyl)hydrazone 404) or treatment with ferric ammonium sulfate (Scheme 19) 405). (+)-Actinidine (9b), the enantiomer of natural alkaloid, is synthesized from acid chloride 265, derived from (+)-pulegone, via vinylketone 267 (Scheme 20) 406). Racemic actinidine (9) is prepared by intramolecular cycloaddition of an acetylene across a pyrimidine ring in 5-(hept-5-yn-2-yl)-4,6-dihydroxypyrimidine (268) followed by chlorination and hydrogenation (Scheme 21) 407). 

Cavill and his co-workers have reported stereospecific syntheses of the enantiomers of two naturally occurring cyclopentanoid monoterpenes, iridodial and nepeta-lactone, from the common precursor D-(+)-pulegone 219, Scheme 35).299 ... 

Velerianine (546), a monoterpene alkaloid, was synthesized by using a Diels-Alder cycloaddition of heterodiene 542 with enol ether 543 (Scheme 69) (70AG(E)891). Heating cyclopentenecarbaldehyde 542 with the enol ether at 200-203°C afforded a 47% yield of the dihydropyranyl ether 544, which consisted of three diastereomers. Hydrolysis of the ether 544 with acid gave iridodial (545), which was condensed with a nitrogen source to afford racemic valerianine (546). 

Examples of dialdehydes which form the enol-hemiacetal group, as postulated by von Schreier and his coworkers for their oxidation products, are homophthalaldehyde (85), iridodial (86), and periodate-oxidized codeine glycols. 

Valerianine (13) was synthesized in racemic form by Franck and coworkers (75) in 1970. Diene condensation of 5-methyl-l-cyclopentene carboxaldehyde (175) with 1,3-dimethoxy propene (176) afforded the tetrahydropyranyl ether 177, which, on acid hydrolysis, afforded 9-methoxy-iridodial (178). This compound was not isolated, but was converted directly to ( )-valerianine 13) with either Fe(NH4)2S04 or NH2OH (Scheme 8)... 

Recent isolation studies have afforded the jasurosides A-D (240) and E-G (241) from the leaves and stems olJasminium urophyllum. A representative structure of jasuroside E (380) is shown. The interesting feature of these iridoids is the manner in which the iridodial-derived groups remain reduced and uncyclized. 

Methyl-2,6-naphthyridine (104) may be derived as shown in Scheme 49. An iridodial such as 385 is cleaved in a manner similar to the formation of 2 to afford a seco-cyclopentano-dihydro-actinidine 386, which can be oxidized and decarboxylated to 104. 

Naturally occurring iridoids and their glycosides are widely distributed in plants and serve as important taxonomic markers. The iridoids were named after ants of the genus Iridomirmex, from which iridodial, iridomyrmecin, and related compounds were isolated and found to be involved in the defense mechanisms of these insects. Similar structures also exist in plants for example nepetalactone from Nepeta cataria L. (Lamiaceae), or teucriumlactone C from Teucrium marum L. have marked properties (the effects of the former on cats earned it some evocative names catnip, Katzenmelisse, herbe-aux-chats). 

Generally iridoids are divided in two categories, iridoids and secoiridoids and these mostly exist as glycosides. Iridoids are also found in aldehydes, alcohols (iridodial (1) iridodiol (2)), alcoholic esters (valepotriates), lactones (irridomyrmecin (3), nepetalactone (4)) and alkaloids (actinidine (5), skytanthine (6)) forms. Secoiridoids on the other hand are formed by cleavage of cyclopentane ring of iridoid. 

---