C25 steroid epimers produced by Penicillium janthinellum, a fungus isolated from fruits Melia azedarach

Abstract

O fungo Penicillium janthinellum, obtido de Melia azedarach, produziu ergosterol, ergosterol 5α,8α-peróxido e uma mistura de esteróides C25 epiméricos de ocorrência restrita na natureza. Os esteróides C25, denominados neociclocitrinóis, possuem o mesmo sistema tetracíclico de anéis presente no ciclocitrinol, o qual foi isolado do fungo Penicillium citrinum, associado a uma esponja, com o mesmo esqueleto biciclo[4:4:1] nos anéis A/B, mas com cadeias laterais diferentes. O P. janthinellum isolado de M. azedarach, foi cultivado sobre milho branco e os três esteróides foram isolados por vários procedimentos cromatográficos e identificados por cuidadosa análise dos dados de RMN, principalmente correlações 1 H -13 C em duas dimensões bem como COSY e TOCSY 1 H -1 H. A origem biossintética dos ciclocitrinóis é discutida.A plant-derived fungus, Penicillium janthinellum, obtained from Melia azedarach, produced ergosterol and ergosterol 5α,8α-peroxide along with a mixture of rare C25 steroid epimers. The C25 steroids, named neocyclocitrinols, shows exactly the same tetracyclic ring system present in cyclocitrinol, which was isolated from a sponge-derived Penicillium citrinum, with the same bicyclo [4:4:1] skeleton at A/B rings, but showing different side chains. The P. janthinellum was cultivated over white corn and the three steroids were isolated by several silica gel based chromatographic procedures and identified by extensive NMR methods, mainly 1 H -13 C correlations and 1 H -1 H COSY and TOCSY. The biosynthetic origin of the cyclocitrinols is also discussed. Keywords: endophytic fungi, Melia azedarach, Penicillium janthinellum, neocyclocitrinols IntroductionSteroid and steroid derived secondary metabolites are frequently found in filamentous fungi. 1 Ergosterol (1) is the precursor of many other microbial steroids. 2 Most of the ergosterol metabolism begins with an oxidative process in double-bonds at C-5(6) and C-7(8) letting to ergosterol 5,8-peroxide, 3 being the endo regioisomer (5α,8α-peroxide) (2) the most frequent, and then hydroxylated products at A/B/C rings are formed. 4 In the present work we have found these sorts of compounds in our chemical studies of endophytic filamentous fungi associated with Meliaceae plants. We previously described the production of polyketides by a Penicillium janthinellum, isolated from fruits of Melia azedarach. 5 Now we report the production of a pair of steroid epimers with a very unusual C25 skeleton, in addition to the regular steroids (1 and 2), when the fungus was cultivated over white corn. These epimers, which are represented here by the structural formula 3, contains a rare bicyclo [4:4:1] system at rings A/B, as in cyclocitrinol (4) and isocyclocitrinol (5) obtained by Amagata et al. 6 from P. citrinum, isolated from a marine sponge. 6 Herein we present spectroscopic evidences, which further support the bicycle system of these compounds and firmly establish the side chain of the new steroid neocyclocitrinol (3). Biosynthetic considerations regard the origin of these st...

Natural Products with Anti‐Bredt and Bridgehead Double Bonds

“…[46] In 2005, Rodrigues-Filho and co-workers reported the isolation of neocyclocitrinol, an epimeric mixture of novel bicyclo[4.4.1]undec-7,10-diene C 25 steroids, akin to the compounds reported by Crews, from the plant-derived fungus Penicillium janthinellum. [49] The isolated compounds showed strong spectroscopic similarities to 46, differing only in the C17 side chain, which aided in the structural elucidation of neocyclocitrinol. Unfortunately, the configuration of the D 20,22 alkene was not established, nor were the absolute configurations determined for the C23 and C24 centers ( Figure 11).…”

“…Zhu and co-workers subsequently re-isolated the neocyclocitrinols, isocyclocitrinol A (43), and 22-acetylisocyclocitrinol A (44), and a series of bicyclo[4.4.1]undec-7,10-diene analogues (47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)) from cultures of the volcanic-ash-derived fungus Penicillium citrinum HGY1-5. [48] Extensive NMR spectral analysis and X-ray crystallography allowed for the unambiguous assignment of the structure and absolute configuration of these compounds.…”

“…Ergosterol (60), which was found to be produced by the fungi, [48,49] is the proposed biosynthetic precursor to these unusual steroids. The proposed mechanism relies on the enzymatic activation of the C19 position to generate an electrophilic center (61), which can react with the D 5,6 alkene with concomitant oxidation of the C6 carbon atom to produce cyclopropane intermediate 62.…”

Esteroides produzidos por Penicillium herquei, um fungo endofítico isolado dos frutos de Melia azedarach (Meliaceae)

“…Essas substâncias são sólidas cristalinas e seus dados de RMN e EM são perfeitamente coincidentes com os descritos na literatura para o ergosterol (1), peróxido de ergosterol (2) e cerevisterol (3). 10 Não foi possível separar a mistura por nenhum método de HPLC. Recentemente foi isolada uma série de esteroides neociclocitrinois de P. citrinum e o estudo biossintético realizado neste trabalho corroborara com a nossa proposta de rota bioquímica.…”

Annularins I and J: New Metabolites Isolated from Endophytic FungusExserohilum rostratum

“…For example, the polyketide citrinin isolated from Penicillium janthinellum completely inhibited the growth of Leishmania braziliensis. 9 Some fungi species of Penicillium and Pestalotiopsis genera produce high diversity of polyketides with antimicrobial activity. 10,11 In another study with a variety of endophytes isolated from Vigueira arenaria and Tithonia diversifolia fungal extracts, important antiparasitic and antimicrobial activities were observed in fungal extracts.…”