Microbial Transformation of Sesquiterpenes, (−)‐Ambrox^® and (+)‐Sclareolide

Abstract

The microbial transformation of (À)-Ambrox ¾ (1), a perfumery sesquiterpene, by a number of fungi, by means of standard two-stage-fermentation technique, afforded ambrox-1a-ol (2), ambrox-1a,11a-diol (3), ambrox-1a,6a-diol (4), ambrox-1a,6a,11a-triol (5), ambrox-3-one (6), ambrox-3b-ol (7), ambrox-3b,6b-diol (8), 13,14,15,16-tetranorlabdane-3,8,12-triol (9), and sclareolide (10) (Schemes 1 and 2). Further incubation of compound 10 with Cunninghamella elegans afforded 3-oxosclareolide (11), 3b-hydroxysclareolide (12), 2a-hydroxysclareolide (13), 2a,3b-dihydroxysclareolide (14), 1a,3b-dihydroxysclareolide (15), and 3b-hydroxy-8-episclareolide (16) (Scheme 3). Metabolites 2 ± 5, 12, 13, and 16 were found to be new compounds. The major transformations include a reaction path involving hydroxylation, ether-bond cleavage and inversion of configuration. Metabolites 11 ± 16 of sclareolide showed significant phytotoxicity ( Table 1). The structures of the metabolites were characterized on the basis of spectroscopic techniques.Introduction. ± In continuation of our studies on biotransformation of bioactive natural and synthetic compounds [1 ± 11], we have recently investigated the biotransformation of two sesquiterpenes, (À)-Ambrox ¾ (1) and ()-sclareolide (10), with various fungal strains. Ambergris, a metabolite of the sperm whale, is one of the mostvaluable animal perfumes, ranking with civet and musk [12] [13]. Ambrein is the major constituent of the ambergris. During exposure in the sea for many years, ambrein is oxidatively decomposed by the action of sea water, air, and sunlight to yield some other odorous compounds [14]. In these compounds, (À)-Ambrox ¾ (1) has a very strong amber-like odor.Fermentation of (À)-Ambrox ¾ (1) with Fusarium lini (NRRL 68751) afforded the new mono-, di-, and trihydroxylated metabolites 2 ± 5, as a result of enantioselective ahydroxylations at C(1), C(6), and C(11), while incubation of compound 1 with Rhizopus stolonifer (ATCC 10404) yielded metabolites 6 ± 8 and ether-cleaved product 9. The ether cleavage through biotransformation is a rare observation. Fermentation of compound 1 with Curvularia lunata (NRRL 2178) yielded metabolites 6 and 7, while its biotransformation with Cunninghamella elegans (NRRL 1392) afforded compounds 6, 7, and ()-sclareolide (10). Compounds 6 ± 10 have already been reported as metabolites of 1 by Cephalosporium aphidicola (wild type), Aspergillus niger (IFO 4049), Aspergillus cellulose (IFO 4040), and Botryatis cinerea (AHU 9424) [15 ± 19]. The oxygenated metabolites of compound 1 did not release any effective odor when compared to 1, except for the ether-cleaved product 9, which exhibited a strong sweet odor quit different from the amber-like odor.

Novel Microbial Transformations of Sclareolide

“…Previously, these compounds were obtained during the microbial transformation of compound 1 by using Curvulria lunata. 8,10) During our screening experiments, we also observed the formation of compounds 5-7 during the biocatalysis of 1 with C. lunata. The 1 H and 13 C and mass spectral data of compounds 5-7 were identical to those of 1b,3b-dihydroxysclareolide, 3-oxosclareolide and 3b-hydroxysclareolide, reported in the literature.…”

“…H-5 has been reported to have a-orientation in compound 1. 8,10) This NOE data led us to assign a-stereochemistry for H-3 and b-stereochemistry for C-3/OH. H-6 exhibited NOE with H 3 -13 (d 1.31), and H 3 -14 (d 0.89).…”

“…The C-13 methyl proton (d 1.30) showed an NOE with the C-14 methyl protons (d 0.92), which further showed spatial couplings with the C-16 methyl protons (d 0.88). After making sure that C-13, C-14 and C-16 methyl group have b orientations, as reported in compound 1, 8,10) the NOESY spectrum was used to establish stereochemistry at C-6. The C-6 methine proton (d 3.75) showed NOE with the C-14 (d 0.92) and C-16 (d 0.88) methyl protons.…”

Fungal Transformation of Dydrogesterone and Inhibitory Effect of Its Metabolites on the Respiratory Burst in Human Neutrophils

“…Structure Elucidation. The structures of 2 -11 were all deduced through comparative spectroscopic (UV, ORD, IR, 1 H-NMR, 13 C-NMR, 2D-NMR) and mass-spectrometric (HR-MS) studies. The structures of the new compounds 10 and 11 are reported herein in full detail.…”

Microbial Transformation of Mestranol by Cunninghamella elegans

“…2) In continuation of our biotransformational studies on bioactive compounds, [2][3][4][5][6][7][8][9][10][11][12][13][14] and in order to study the effects of substitution on metabolism, compounds 1 and 4 were now incubated with Cunninghamella elegans. The 3-O-methylated derivative of compound 5, i.e.…”