PubMed · 1549729
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Y Katsube. 1992. [Characterization of structure determined by X-ray diffraction methods].. https://pubmed.ncbi.nlm.nih.gov/1549729/
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Parnafungins A-D (1-4) are fungal natural products that inhibit eukaryotic poly(A)-polymerase and were first discovered by Merck & Co., Inc., through a Candida albicans Fitness Test (CaFT) screening program. The biological activity of parnafungins is a result of the unique fused hexacyclic structure highlighted by a 5-isoxazolidinone (5ILD) N-heterocycle. In this work, we characterize the complete biosynthetic pathway of parnafungins through heterologous reconstitution and enzymatic assays. Nearly half of the 26-gene biosynthetic gene cluster of parnafungin is responsible for the production of a known polyketide natural product, blennolide C. Starting from the blennolide C fragment, a three-enzyme cascade involving CoA-ligase ParJ, P450 ParO, and DUF829 ParD catalyzes the formal biaryl cross-coupling between blennolide C and anthranilate. Subsequent oxidative cyclization generates a phenanthridine product that is then reduced by atypical short-chain reductase ParT. N-Hydroxylation by flavin-dependent monooxygenase ParB and subsequent lactonization catalyzed by a homologue of dienenolactone hydrolase ParF form the 5ILD ring and complete the biosynthesis of 1 and 2. Methylation of 1 forms parnafungin C (3), and lastly epoxidation forms parnafungin D (4). Together, our work revealed the chemical logic and enzymology in extending the biosynthetic pathway of a well-characterized natural product, blennolide C, to introduce considerable additional structural diversity that affords parnafungins with unique biological activity.
C27H40O7, M(r) = 476.61, monoclinic, P2(1), a = 17.440 (5), b = 13.267 (1), c = 12.168 (2) A, beta = 110.49 (8) degrees, V = 2637.3 (9) A3, Z = 4, Dx = 1.20 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 7.04 cm-1, F(000) = 1032, T = 293 K, R = 0.048, wR = 0.068 for 5590 observed reflections with (Fo)2 > 2 sigma [(Fo)2]. The structure contains two crystallographically independent molecules in the asymmetric unit that have almost identical geometry. Rings A, B and C have chair conformations and the D ring assumes a half-chair conformation in both molecules. The progesterone side chain has a conformation typical for other 17 alpha-ester steroids; the C(16)--C(17)--C(20--O(20) torsion angles are -18.2 (5) and -15.0 (4) degrees for the first and the second molecule respectively.
C13H20NO2+.Br-, M(r) = 302.2, monoclinic, P2(1)/c, a = 8.697 (2), b = 12.741 (3), c = 12.940 (2) A, beta = 103.39 (2) degrees, V = 1394.9 (8) A3, Z = 4, Dx = 1.439 g cm-3, lambda (Mo K alpha) = 0.71073 A, mu = 29.1 cm-1, F(000) = 624, T = 296 K, R = 0.038 for 1662 observations with I > 2 sigma (I) (of 2460 unique data). The morpholinium ring adopts the chair conformation with endocyclic torsion angle magnitudes 49.1 (4)-61.9 (4) degrees. The hydroxyl group is in the axial position of the morpholinium ring, with C--OH bond distance 1.401 (4) A. The hydroxy H atom points towards a Br ion; the interaction has O...Br distance 3.292 (2) A, H...Br distance 2.61 (3) A, and angle at H 160 (4) degrees.