Martin G. Peter

Cuticular sclerotization in insects

Abstract The insect cuticle is an extracellular structure covering the total outer surface of the animal and providing protection against harmful influences from the environment. The mechanical properties of cuticles may vary considerably, and pronounced regional differences are generally observed. The properties may also change during development, and it can be assumed that the physical and chemical properties of all cuticular regions tend to be close to the optimal for proper physiological function during all developmental stages. Cuticular regions can be stabilized by the process of sclerotization, whereby o-diphenols are oxidatively incorporated into the material. Our current knowledge of the sclerotization process is reviewed, and it is suggested that the main features of the chemistry of sclerotization probably have been established, and that the major questions now remaining concern the precise regional and temporal control of the process.

Binding and degradation of juvenile hormone III by haemolymph proteins of the Colorado potato beetle: A re-examination

The haemolymph of the adult Colorado potato beetle, Lepinotarsa decemlineata Say, contains a high molecular weight (MW > 200,000) JH-III specific binding protein. The Kd value of the protein for racemic JH-III is 1.3 ± 0.2 × 10−7 M. It has a lower affinity for racemic JH-I and it does not bind JH-III-diol or JH-III-acid. The binding protein does discriminate between the enantiomers of synthetic, racemic JH-III as was determined by stereochemical anaysis of the bound and the free JH-III. Incubation of racemic JH-III with crude haemolymph results in preferential formation of (10S)-JH-III-acid, the unnatural configuration. The JH-esterase present in L. decemlineata haemolymph is not enantioselective. It is concluded that the most important function of the binding protein is that of a specific carrier, protecting the natural hormone against degradation by esterases. The carrier does not protect JH-I as efficiently as the lower homologue.

Cuticle-catalyzed coupling between N-acetylhistidine and N-acetyldopamine

Several types of insect cuticle contain enzymes catalyzing the formation ofof adducts between N-acetyldopamine (NADA) and N-acetylhistidine (NAH). Two such adducts, NAH-NADA-I and NAH NADA-II, have been isolated and their structures determined. n nIn one of the adducts the link connecting the two residues occurs between the I-position (s-position) in the NADA side chain and the 1-N atom (τ-N) in the imidazole ring of histidine. Diphenoloxidase activity alone is not sufficient for formation of this adduct, whereas extracts containing both diphenoloxidase and o-quinone-p-quinone methide isomerase activities catalyze the coupling reaction. The adduct consists of a mixture of two diastereomers and they are presumably formed by spontaneous reaction between enzymatically produced NADA-p-quinone methide and N-acetylhistidine. n nThe other adduct has been identified as a ring addition product of N-acetylhistidine and NADA. In contrast to the former adduct it can be formed by incubation of the two substrates with mushroom tyrosinase alone. n nAn adduct between N-acetylhistidine and the benzodioxan-type NADA-dimer is produced in vitro, when the N-acetylhistidine-NADA adduct is incubated with NADA and locust cuticle containing a 1,2-dehydro-NADA generating enzyme system. n nTrimeric NADA-polymerization products of the substituted benzodioxan-type have been obtained from in vivo sclerotized locust cuticle, confirming the ability of cuticle to produce NADA-oligomers. n nThe results indicate that some insect cuticles contain enzymes promoting linkage of oxidized NADA to histidine residues. It is suggested that histidine residues in the cuticular proteins can serve as acceptors for oxidized NADA and that further addition of NADA-residues to the phenolic groups of bound NADA can occur, resulting in formation of protein-linked NADA-oligomers. The coupling reactions identified may be an important step in natural cuticular sclerotization.

Catecholamine-protein conjugates: Isolation of an adduct of N-acetylhistidine to the side chain of N-acetyldopamine from an insect-enzyme catalyzed reaction

Nα-Acetyl-Nτ-[1-(3,4,-dihydroxyphenyl)-2-N-acetylamino-ethyl]-histidine (4) was isolated from a biomimetic reaction containing N-acetyl-dopamine 1, Nα-acetyl-L-histidine and cuticle of silkmoth larvae as an enzyme source. The formation of 4 suggests an 1,6-addition of the Nτ imidazole nitrogen to the p-quinone methide 3.

Synthesis of N-acetylsugar-β-trans-glycosides : facile one-pot transglycosylation of epoxypentyl tri-O-acetyl-N-acetylglucosamine

Abstract Glycosides 10 and 11 were prepared from epoxypentyl β-D-N-acetylglucosamine 8 under mild conditions, using TMS triflate as the promotor. Presumably, this novel reaction proceeds via in situ activation of the intermediate oxazoline 9 .

Oxidative coupling of dopa with resorcinol and phloroglucinol: Isolation of adducts with an unusual tetrahydromethanobenzofuro[2,3-d]azocine skeleton

Abstract Under biomimetic conditions, both phloroglucinol and resorcinol cause significant inhibition of the oxidative conversion of dopa to dopachrome, a key step in the biosynthesis of melanin pigments. The major product (λmax = 377 nm) from oxidation of dopa in the presence of phloroglucinol was characterized as 2, containing the unusual tetrahydromethanobenzofuroazocine ring system. Another product, formed in somewhat smaller amount, was formulated as 3, arising from coupling of phloroglucinol with 2 dopaquinone derived units. Analogous cross coupling adducts 4 and 5 were obtained by reaction of dopa or dopa methylester with resorcinol, respectively. These results suggest the trapping of labile dopaquinone, generated in situ from oxidation of dopa, by the reactive phenolic compounds, leading to the novel adducts 2, 4 and 5.

Synthesis of l-Histidine and (-)-Spinacine Chitooligosyl Amides1

Abstract The synthesis of N-(2-acetamido-4-O-[2-acetamido-4-O-{2-acetamido-2-deoxy-β-D-glucopyranosyl}-2-deoxy-β-D-glucopyranosyl]-2-deoxy-β-D-glucopyranosyl)-L-histidine amide (3), N-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(6S)-4,5,6,7-tetrahy-droimidazo[4,5-c]pyridine-6-carboxylic amide (4) and N-(2-acetamido-4-O-[2-acetamido-2-deoxy-β-D-glucopyranosyl]-2-deoxy-β-D-glucopyranosyl)-(6S)-4,5,6,7-tetrahydroimidazo[4,5-c]pyridine-6-carboxamide (5) is achieved via coupling of the appropiate glycosylamines with Boc-protected L-histidine or with (6S)-4,5,6,7-tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acid ((-)-spinacine), respectively, by means of EEDQ and subsequent deprotection.

Catecholamine-protein conjugates: isolation of 4-phenylphenoxazin-2-ones from oxidative coupling of N-acetyldopamine with aliphatic amino acids

4-Phenylphenoxazinones 4 were isolated after biomimetic oxidation, using diphenoloxidases of insect cuticle, mushroom tyrosinase, or after autoxidation of N-acetyldopamine (1) in the presence of β-alanine, β-alanine methyl ester or N-acetyl-L-lysine. They are formed presumably by addition of 2-aminoalkyl-5-alkylphenols 2 to the o-quinone of biphenyltetrol 3 which, in turn, arises from oxidative coupling of 1. The structures of 4 present the first examples for the assembly of reasonably stable intermediates in the rather complex process of chemical modifications of aliphatic amino acid residues by o-quinones.

The inhibitory effect of sinefungin on juvenile hormone biosynthesis and development in locusts

Abstract The antibiotic fungal metabolite sinefungin is a potent inhibitor of S-adenosylmethionine-acceptor methyltransferases. Its effect on insect metabolism and especially on corpora allata farnesoic acid methyltransferase, which catalyzes the penultimate step of juvenile hormone biosynthesis, was investigated in Locusta migratoria. Injection of sinefungin results in a delay of imaginal molt and in suppression of ovary development. Isolated corpora allata are unable to synthesize juvenile hormone III in the presence of more than 1.0 mM sinefungin. In a cell-free system containing the S-adenosylmethionine-dependent farnesoic acid methyltransferase from corpora allata sinefungin is a competitive inhibitor of the synthesis of methylfarnesoate with Ki of 1 μM.