Biomedical subjects
Publications and source records attributed to J Meinwald.
The blood of the Mexican bean beetle (Epilachna varivestis) contains a homotropane alkaloid, euphococcinine (1). The beetles 'reflex bleed' when disturbed, thereby deploying the alkaloid, which is provenly deterrent to spiders and ants. Newly emerged adults lack the alkaloid, but the compound builds up to deterrent levels in their blood within days. Eggs and larvae of Epilachna are devoid of the compound.
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Two sympatric species of Asian arctiid moths (Creatonotos spp.) use a sequential, dual luring and mating system. After sunset males pneumatically expand their coremata from a cavity between the abdominal sternites 7 and 8 and release their pheromone. They attract other males and thus, scent-emitting male groups may develop. About 30 min later females are attracted to the calling males. Upon contact with a female the male's corema deflates and mating follows. After 1-2 h the male calling subsides and now the remaining virgin females continue to emit their pheromone bouquet from internal, tubular glands located in the dorsal part of the abdomen, rostrad from tergite 8/9. This attracts males and further matings occur.- The coremata are huge, pneumatically eversible organs composed of two pairs of tubes, up to 37 mm long, each covered by ca. 3000 scent hairs (scales). There is a giant epidermal (trichogen) gland cell at the base of each hair. One large corema may contain up to 0.5 mg of the pheromone, hydroxydanaidal. The internal, tubular female glands are antler shaped; their air-filled lumen is ventilated by abdominal pumping. The major components of the female attractant are (Z,Z,Z)-3,6,9-heneicosatriene and (Z,Z)-2 (2,5-octadienyl)-3-undecyloxirane with different ratios in the two species. One of the minor components, common to both species, is (Z,Z,Z)-3,6,9-tricosatriene. Only the male antennae possess specialized receptor cells for the female attractants; other antennal cells of both sexes respond to the male pheromone.
The defensive anal effluent discharged by Silpha americana in response to disturbance contains a mixture of steroids stemming from a glandular annex of the rectum. The compounds have been characterized as 15 beta-hydroxyprogesterone (1, principal component), 5 beta-pregnan-15 beta-ol-3,20-dione (2), 5 beta-pregnan-3 alpha, 15 beta-diol-20-one (3), 5 beta-pregnan-7 beta, 15 beta-diol-3,20-dione (4), 5 beta-pregnan-3 alpha, 7 beta, 15 beta-triol-20-one (5), 5 beta-pregnan-16 alpha-ol-3,20-dione (6), and 5 beta-pregnan-3 alpha, 16 alpha-diol-20-one (7), none previously found in insects. Bioassays with jumping spiders showed compounds 1 and 6 to be feeding deterrents at the 1 microgram level.
The biosynthetic conversion of a pyrrolizidine alkaloid (heliotrine, IV) to a male moth pheromone (hydroxydanaidal, III) is found to proceed with inversion of configuration at the remaining asymmetric center (C-7).
Two straight-chain C(15) fish antifeedants have been isolated from the sea hare Aplysia brasiliana. Chemical, spectral, and x-ray diffraction studies led to the characterization of these medium-ring ethers as brasilenyne (2) and cis-dihydrorhodophytin (3). The oxonin ring system of 2 is novel in nature. Biosynthetic considerations permit the postulation that a third compound, a noncrystalline congener of these compounds, is cis-isodihydrohodophytin (4).
Feeding tests with thrushes (Hylocichla spp.) led to the isolation of three novel steroid pyrones from fireflies (Photinus ignitus and P. marginellus) responsible, in part at least, for the unpalatability of these insects to the birds. The term lucibufagin is coined for these steroidal pyrones. The closest known relatives of lucibufagins are the familiar cardiotonic bufadienolides, found in certain toads and plants.
A novel cyanogenetic compound benzoyl cyanide, was isolated from the defensive secretion of 3 polydesmoid millipeds (Pseudopolydesmus seratus, Apheloria corrugata and A. trimaculata). The secretion of the 3 species also contains mandelonitrile and benzaldehyde, and that of P. serratus contains mandelonitrile benzoate, benzoic acid, isovaleric acid, myristic acid and stearic acid.
Analyses of the chief volatile constituents of the defensive secretions of three oplionids were carried out. Leiobunum nigripalpi produces three closely related C7 compounds: E-4-methyl-4-hexen-3-one(I), 4-methylhexan-3-one(II), and 4-methylhexan-3-ol(III), along with E-4-methyl-4-hepten-3-one(IV), E,E-2,4-dimethylhexa-2,4-dienal(IX), and a minor, unidentified component. L. leiopenis secretion contains E-4-methyl-4-hepten-3-one(IV), 4-methylheptan-3-one(V), E,E-2,4-dimethylhexa-2,4-dien-1-ol(VII), and E,E-2,4-dimethylhepta-2,4-dien-1-ol(VIII). L. calcar yields chiefly E-4,6-dimethyl-6-octen-3-one(VI) and E,E-2,4-dimethylhexa-2,4-dien-1-ol(VII). Six of these compounds are new natural products. The structures of these compounds, which can be regarded either as polyketide-derived or as modified isoprenoids, raise interesting biosynthetic questions.
The defensive secretion of larvae of the chrysomelid beetle Plagiodera versicolora contains two unstable, volatile methylcyclopentanoid terpenes: a dialdehyde (chrysomelidial) isomeric with dolichodial and anisomorphal, and a closely related enol lactone (plagiolactone). Chrysomelidial and plagiolactone are shown to have structures III and IV on the basis of a detailed analysis of their spectra, coupled with chemical transformations to products of known structure.
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A nitrogen-containing terpene 6,6-dimethyl-2-azaspiro[4.4]non-1-ene (polyzonimine) was isolated from the defensive secretion of the milliped Polyzonium rosalbum. Polyzonimine, which is repellent to such natural enemies of the milliped as ants, acts as a topical irritant to insects (10-4 M induces scratching in cockroaches). Its structure was confirmed by a five-step synthesis starting from 2,2-dimethyl-7-oxabicyclo[4.1.0]heptane.
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Larvae of the sawfly Neodiprion sertifer (Hymenoptera: Diprionidae), when disturbed, discharge an oily oral effluent essentially identical chemically to the terpenoid resin of its host plant (Pinus sylvestris). The resin is sequestered by the larva upon feeding, and stored in two compressible diverticular pouches of the foregut. The fluid is effectively deterrent to predators. The defensive use by an insect of a plant resin provides an instance of secondary utilization by a herbivore of the protective chemical weaponry of its host.
The C/D-cisD-norandrostanes 1a, 1b, 1c, 2a, 2b, and 2c were prepared and their reactivity studied. Whereas carbonium ion reactions of 1b and 1c are readily interpreted on the basis of their assigned stereochemistry, reactions of 2b and 2c suggest that these compounds react via conformations in which the 16beta-substituents are pseudoequatorial, requiring a ring C boat conformation as shown in formula 3b. X-ray crystallographic studies on 1a and 2a establish that while 1a has the expected conformation, 2a exists preferentially with ring C in the boat form. Molecular models suggest that this is the result of severe nonbonded interactions in the alternative conformation (3a) in which a chair C ring is retained.
The petals of the black-eyed susan (Compositae: Rudbeckia hirta) contain three flavonol glucosides (6,7-dimethoxy-3',4',5-trihydroxyflavone-3-O-glucoside, patulitrin, and quercetagetin). These compounds, which show intense spectral absorption at 340 to 380 nanometers, are restricted in distribution to the petal bases, which are ultraviolet absorbing as a result. Such ultraviolet-absorbing petal zones, known as "nectar guides," are invisible to us, but are visible and of orientation value to the pollinating insect that lands on the flower in search for food. This is the first time that ultraviolet absorption in a nectar guide has been interpreted in chemical terms. In view of the widespread occurrence of flavonols in flowers, it is suggested that these pigments serve specifically for demarcation of ultraviolet petal patterns visible and relevant to insects.
Three species of gyrinid beetles (Gyrinus ventralis, Dineutes hornii, and D. serrulatus) have been found to produce the nor-sesquiterpenoid aldehyde gyrinidal in the secretion of their pygidial defensive glands. This highly functionalized terpene is shown to be (E,E,E)-3,7-dimethyl-8,11-dioxo-2,6,9-dodecatrienal on the basis of spectral evidence and chemical degradation. While a very wide range of sesquiterpenoid structures occur in nature, gyrinidal appears to be the most highly oxidized acyclic sesquiterpene known.