Ecdysone metabolism in Pieris brassicae during the feeding last larval instar

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Abstract
Ecdysone metabolism in Pieris brassicae during the feeding last larval stage was investigated by using 3H‐labeled ecdysteroid injections followed by high‐performance liquid chromatographic (HPLC Abbreviations: 3DE = 3‐dehydroecdysone; 3D20E = 3‐dehydro‐20‐hydroxyecdysone; 2026E = 20,26‐dihydroxyecdysone; E = ecdysone; Eoic = ecdysonoic acid; 2026E′ = 3‐epi‐20,26‐dihydroxyecdysone; E′ = 3‐epiecdysone; E′oic = 3‐epiecdysonoic acid; E′8P = 3‐epiecdysone 3‐phosphate; 20E′ = 3‐epi‐20‐hydroxyecdysone; 20E′3P = 3‐epi‐20‐hydroxyecdysone 3‐phosphate; FT = Fourier transform; HPLC = high‐performance liquid chromatography; 20E = 20‐hydroxyecdysone; 20Eoic = 20‐hydroxyecdysonoic acid; NMR = nuclear magnetic resonance; NP‐HPLC = normal phase HPLC; RP‐HPLC = reverse phase HPLC; TFA = trifluoroacetic acid; Tris = tris(hydroxymethyl)‐aminomethane. ) analysis of metabolites. Metabolites were generally identified by comigration with available references in different HPLC systems. Analysis of compounds for which no reference was available required a large‐scale preparation and purification for their identification by 1H nuclear magnetic resonance spectrometry.The metabolic reactions affect the ecdysone molecule at C‐3, C‐20, and C‐26, leading to molecules which are modified at one, two, or three of these positions. At C‐20, hydroxylation leads to 20‐hydroxyecdysteroids. At C‐26, hydroxylation leads to 26‐hydroxyecdysteroids which can be further converted into 26‐oic derivatives (ecdysonoic acids) by oxidation. At C‐3, there are several possibilities: there may be oxidation into 3‐dehydroecdysteroids, or epimerization possibly followed by phosphate conjugation.Thus, injected 20‐hydroxyecdysone was converted principally into 20‐hydroxyecdysonoic acid, 3‐dehydro‐20‐hydroxyecdysone, and 3‐epi‐20‐hydroxyecdysone 3‐phosphate. Labelled ecdysone mainly gave the same metabolites doubled by a homologous series lacking the 20‐hydroxyl group.