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Biomedical subjects

J Meinwald

Publications and source records attributed to J Meinwald.

At least 19 recordsLinked to original sources
PubMed2001

Attractive and defensive functions of the ultraviolet pigments of a flower (Hypericum calycinum).

The flower of Hypericum calycinum, which appears uniformly yellow to humans, bears a UV pattern, presumably visible to insects. Two categories of pigments, flavonoids and dearomatized isoprenylated phloroglucinols (DIPs), are responsible for the UV demarcations of this flower. Flavonoids had been shown previously to function as floral UV pigments, but DIPs had not been demonstrated to serve in that capacity. We found the DIPs to be present in high concentration in the anthers and ovarian wall of the flower, suggesting that the compounds also serve in defense. Indeed, feeding tests done with one of the DIPs (hypercalin A) showed the compound to be deterrent and toxic to a caterpillar (Utetheisa ornatrix). The possibility that floral UV pigments fulfill both a visual and a defensive function had not previously been contemplated. DIPs may also serve for protection of female reproductive structures in other plants, for example in hops (Humulus lupulus). The DIPs of hops are put to human use as bitter flavoring agents and preservatives in beer.

Animals↗
PubMed2001

Synthesis of unsaturated polyazamacrolides from the ladybird beetle Subcoccinella vigintiquatuorpunctata.

The pupal defensive secretion of the ladybird beetle Subcoccinella vigintiquatuorpunctata consists of a mixture of macrocyclic polyamines (polyazamacrolides, PAMLs) dominated by three dimeric, 30-membered bislactones (1, 2, and 3), which represent the three possible head-to-tail combinations of the two building blocks (S)-(Z)-11-(2-hydroxyethylamino)-5-tetradecenoic acid (4) and (S)-(5Z,8Z)-11-(2-hydroxyethylamino)-5,8-tetradecadienoic acid (5). We now report the synthesis of these three alkaloids via a route involving the nucleophilic opening of a chiral aziridine as a common step.

Animals↗
PubMed2001

Synthesis and ring contraction reactions of polyazamacrolides.

The synthesis of three analogues of the single most abundant component of a ladybird beetle (Epilachna borealis) defensive secretion, the trimeric 42-membered polyazamacrolide PAML 681, is described. Construction of the nonnatural macrocyclic trimers began with the preparation of the corresponding monomeric segments, followed by their oligomerization and a final macrolactonization step of the activated linear trimeric hydroxy acid. The relative rates of the O-to-N acyl migrations that are characteristic of PAML 681 itself, as well as of the synthetic analogues, were investigated. These studies showed that changes in the substitution pattern adjacent to the nucleophilic nitrogen atom, along with changes in the size of the oxaazacyclic intermediates, have substantial effects on the polyazamacrolide rearrangement rates.

Animals↗
PubMed2001

Production of a cyanogenic secretion by a thyridid caterpillar (Calindoea trifascialis, Thyrididae, Lepidoptera).

The thyridid caterpillar, Calindoea trifascialis, when disturbed, emits a defensive secretion from two sac-like glands that open dorsolaterally on the first abdominal segment. The larva has two arm-like protuberances that project outward from the body just in front of the gland openings. These "arms", which are wetted by secretion when the larva activates its glands, appear to function specifically for administration of the fluid. A primary component of the secretion in mandelonitrile, a cyanogenic compound, but the fluid also contains other potential deterrents, including benzaldehyde, benzoic acid, (E,E)-alpha-farnesene, and 3-methylbutyl-3-methylbutanoate. Tests done in the field in Vietnam, where the species is native, showed the secretion to be protective against ants.

Acetonitriles↗
PubMed2001

A cyanoallyl glucoside from Alliaria petiolata, as a feeding deterrent for larvae of Pieris napi oleracea.

Alliarinoside, a feeding inhibitor against early instar larvae of Pieris napi oleracea, was isolated from the foliage of Alliaria petiolata and characterized as (2Z)-4-(beta-D-glucopyranosyloxy)-2-butenenitrile (1) by spectroscopic methods. The structural assignment was confirmed by synthesis of peracetylated alliarinoside (2) and its 2E isomer (3). A sample of synthetic 1 was isolated by preparative HPLC from the hydrolysis of the 2Z acetate. Feeding inhibition assays showed comparable activity for the synthetic and natural glycosides.

Animals↗
PubMed2001

Evaluation of the synthetic major component of the sex pheromone of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).

In wind-tunnel bioassays, dispensers loaded with 1 microg of the synthetic major component (3E,8Z, 11Z)-3,8,11-tetradecatrienyl acetate (TDTA) of the sex pheromone emitted by Tuta absoluta (Meyrick) females were found to be highly attractive to conspecific males. Field experiments were conducted to evaluate the efficacy of five trap designs. The best trap, baited with 100 microg of the synthetic sex pheromone caught on average 1,200 males per trap per night, while those baited with virgin females caught only 201 males. The male response to this pheromone is restricted to the same early-morning time window during which females exhibit calling behavior. The high biological activity of the synthetic pheromone suggests that it could be useful for pest monitoring and in mating disruption.

Acetates↗
PubMed2000

Chemical defense: bestowal of a nuptial alkaloidal garment by a male moth on its mate.

Males of the moth Cosmosoma myrodora (Arctiidae) acquire pyrrolizidine alkaloid by feeding on the excrescent fluids of certain plants (for instance, Eupatorium capillifolium). They incorporate the alkaloid systemically and as a result are protected against spiders. The males have a pair of abdominal pouches, densely packed with fine cuticular filaments, which in alkaloid-fed males are alkaloid laden. The males discharge the filaments on the female in bursts during courtship, embellishing her with alkaloid as a result. The topical investiture protects the female against spiders. Alkaloid-free filaments, from alkaloid-deprived males, convey no such protection. The males also transmit alkaloid to the female by seminal infusion. The systemic alkaloid thus received, which itself may contribute to the female's defense against spiders, is bestowed in part by the female on the eggs. Although paternal contribution to egg defense had previously been demonstrated for several arctiid moths, protective nuptial festooning of a female by its mate, such as is practiced by C. myrodora, appears to be without parallel among insects.

Animals↗
PubMed2000

Chiral silylation reagents for the determination of absolute configuration by NMR spectroscopy.

We have investigated the use of chiral silylating reagents as analytical probes for determining the absolute stereochemistry of natural products by NMR spectroscopy. These reagents are prepared in high chemical yield in one step and can be used to derivatize chiral allylic alcohols which are incompatible with ester-based methodologies. Microscale ( approximately 400 nmol) derivatization conditions have been defined. The resulting siloxane diastereomers are readily distinguished by their (1)H NMR spectra.

Animals↗
PubMed2000

Chemical defense against predation in an insect egg.

The larva of the green lacewing (Ceraeochrysa cubana) (Neuroptera, Chrysopidae) is a natural predator of eggs of Utetheisa ornatrix (Lepidoptera, Arctiidae), a moth that sequesters pyrrolizidine alkaloids from its larval foodplant (Fabaceae, Crotalaria spp.). Utetheisa eggs are ordinarily endowed with the alkaloid. Alkaloid-free Utetheisa eggs, produced experimentally, are pierced by the larva with its sharp tubular jaws and sucked out. Alkaloid-laden eggs, in contrast, are rejected. When attacking an Utetheisa egg cluster (numbering on average 20 eggs), the larva subjects it to an inspection process. It prods and/or pierces a small number of eggs (on average two to three) and, if these contain alkaloid, it passes "negative judgement" on the remainder of the cluster and turns away. Such generalization on the part of the larva makes sense, because the eggs within clusters differ little in alkaloid content. There is, however, considerable between-cluster variation in egg alkaloid content, so clusters in nature can be expected to range widely in palatability. To check each cluster for acceptability must therefore be adaptive for the larva, just as it must be adaptive for Utetheisa to lay its eggs in large clusters and to apportion alkaloid evenly among eggs of a cluster.

Animals↗
PubMed2000

Cycloalkene budding: mass spectrometric studies of competitive and dual cycloalkene extrusion reactions from doubly unsaturated aldehyde N,N-dimethylhydrazones.

Mass spectral fragmentation pathways of four doubly unsaturated aldehyde N,N-dimethylhydrazones were investigated using EI-MS and tandem mass spectrometry (MS/MS) under electron ionization and collisionally activated decomposition (CAD) conditions. Cyclopentene extrusion was found to be slightly favored over cyclohexene loss in a hydrazone capable of losing either cycloalkene. Evidence for the regeneration of a chain-shortened iminium radical cation as a result of cycloalkene extrusion was provided by studying substrates capable of undergoing successive cycloalkene budding sequences. EI-MS of these compounds shows sequential loss of both cyclopentene and cyclohexene, in accord with expectations for a cascade mechanism. Although these MS/MS experimental results are also compatible with alternative mechanisms which would entail the simultaneous loss of both neutral cycloalkenes or of a macrocyclic diene, a rapid cascade of cycloalkene budding accounts best for the experimental observations.

Alkenes↗
PubMed2000

Spray mechanism of the most primitive bombardier beetle (Metrius contractus).

The bombardier beetle Metrius contractus discharges its defensive secretion as a froth that clings to its body. When attacked from the rear, it allows the froth to build up over the gland openings near the abdominal tip; when attacked from the front, it conveys the secretion forwards along special elytral tracks. M. contractus has two-chambered defensive glands typical of bombardier beetles, and its secretion, like that of other bombardiers, is quinonoid and hot. Its frothing mechanism, however, is unique for bombardiers and possibly illustrative of the ancestral glandular discharge mechanism of these beetles. M. contractus, thus, could be the least derived of extant bombardiers.

Animals↗
PubMed1999

Miriamin, a defensive diterpene from the eggs of a land slug (Arion sp.).

The eggs of the land slug Arion sp. contain a diterpene, miriamin, characterized as a polyoxygenated geranylgeraniol derivative. In bioassays with a coccinellid beetle, Harmonia axyridis, miriamin was shown to be potently antifeedant, indicating that the compound plays a protective role in nature. It is suggested that mucilaginous soil-inhabiting organisms, given their intense exposure to pathogens and predators, may be a rich source of chemical defensive agents.

Animals↗
PubMed1999

Reptilian chemistry: characterization of dianeackerone, a secretory product from a crocodile.

The major volatile component in the paracloacal glandular secretion of the adult African dwarf crocodile (Osteolaemus tetraspis) was isolated and characterized as a 19-carbon aromatic ketone, dianeackerone (3,7-diethyl-9-phenyl-2-nonanone). This ketone is absent from the secretion of immatures. Careful examination of dianeackerone samples isolated from individual adults revealed that this ketone occurs as both the (3S, 7S) and (3S, 7R) stereoisomers, with different individuals presenting strikingly different ratios of the isomeric forms. Our initial suspicion that the stereoisomeric dianeackerones might be indicators of gender proved untenable, leaving the role of these glandular constituents a challenge for future study.

Alligators and Crocodiles↗
PubMed1999

Reptilian chemistry: characterization of a family of dianeackerone-related steroidal esters from a crocodile secretion.

The African dwarf crocodile, Osteolaemus tetraspis (Crocodilidae, Reptilia), possesses a pair of skin glands, the paracloacal glands, the secretion of which is thought to be used to mark nest sites or attract mates. Ten aromatic steroidal esters were isolated from this secretion and characterized on the basis of NMR spectroscopic investigations, electrospray ionization-MS analyses, and chemical degradation. These esters, which account for more than 90% of the paracloacal glandular secretion, are derived from either cholesterol or cholestanol, esterified with a C-20 or C-22 acid closely related to dianeackerone, the only significant volatile compound found in this secretion.

Alligators and Crocodiles↗
PubMed1998

Polyazamacrolides from ladybird beetles: ring-size selective oligomerization.

The pupal defensive secretion of the 24-pointed ladybird beetle, Subcoccinella vigintiquatuorpunctata, consists of a mixture of macrocyclic polyamines, dominated by the three dimeric, 30-membered macrocycles 11-13, derived from the two building blocks 11-(2-hydoxyethylamino)-5-tetradecenoic acid (9) and 11-(2-hydoxyethylamino)-5,8-tetradecadienoic acid (10). Smaller amounts of the four possible cyclic trimers of 9 and 10 were also detected, corresponding to 45-membered macrocycles. Structural assignments were based on NMR-spectroscopic investigations and HPLC-MS analyses. In addition, the all-S absolute configuration of the S. vigintiquatuorpunctata macrocycles was determined by comparison of derivatives of the natural material with enantiomerically pure synthetic samples. Comparing this alkaloid mixture with that of the pupal defensive secretion in related ladybird beetle species indicates that the degree of oligomerization of the 2-hydroxyethylamino carboxylic acid building blocks can be carefully controlled by the insects.

Alkaloids↗
PubMed1998

Combinatorial chemistry in insects: a library of defensive macrocyclic polyamines.

The pupal defensive secretion of the coccinellid beetle Epilachna borealis is composed principally of a combinatorial library of macrocyclic polyamines. These compounds constitute a previously unrecognized family of natural products, characterized by extremely large-ring lactonic structures derived from a small set of (2-hydroxyethylamino)alkanoic acids. The combinatorial assembly of these simple building blocks generates a high degree of structural diversity, which is further increased by slow, spontaneous intramolecular rearrangement of the macrocycles.

Amino Acids↗
PubMed1998

Mirasorvone: a masked 20-ketopregnane from the defensive secretion of a diving beetle (Thermonectus marmoratus).

The sunburst diving beetle, Thermonectus marmoratus, ejects a milky fluid from its prothoracic defensive glands when disturbed. Two major volatile components of this secretion are steroids; cybisterone (structure 7) constitutes about 20% of the volatiles, and a new steroid, mirasorvone, about 50%. Mirasorvone is assigned an 18-oxygenated pregnane structure (structure 9) on the basis of extensive spectroscopic data. Although no 18-oxygenated steroid has been described previously from an insect source, a closely related hormone with mineralocorticoid activity, 18-hydroxydeoxycorticosterone (structure 13), has been isolated from the adrenal glands of rats.

Animals↗