¹³C NMR-Based Empirical Rules to Determine the Configuration of Fatty Acid Butanolides. Novel γ-Dilactones from Pterogorgia spp

Abstract

Diastereomeric gamma-dilactones isolated from Pterogorgia spp allowed the establishment of (13)C NMR-based empirical rules to determine the relative stereochemistry of 3-alkyl-4-hydroxy-5-methyl-2(5H)-dihydrofuranones, gamma-lactone moieties ubiquitous in many bioactive synthetic and natural products. An NMR-based method using Pirkle's reagent at low temperature allowed the absolute configuration of the naturally occurring dibutenolides to be unambiguously determined. A biogenetic pathway that involves oxidation of long-chain (C16:0 and C18:0) fatty acids is proposed. [structure: see text]

Coprinuslactone protects the edible mushroom Coprinus comatus against biofilm infections by blocking both quorum‐sensing and MurA

“…The relative configuration of the ring substituents were determined by comparison with NMR resonances of known compounds. NMR data of (2R,3R,4S)‐ and (2S,3R,4S)−2‐methyl‐3,4‐dihydroxypentanoic acid 1,4‐lactone, 5 S ,3′ R ,4′ S ,5′ S ‐ and 5 S ,3′ S ,4′ S ,5′ S ‐hydroxyancepsenolide as well as (2S*,3R*,4S*)‐2‐n‐hexadecyl‐3,4‐dihydroxypentanoic acid 1,4‐lactone (Lorenzo et al ., ) revealed that a trans ‐configuration of the 3‐OH to the 4‐methyl group causes a shielding of about δ H 0.3–0.7 ppm and a deshielding of about δ C 5 ppm compared with a cis ‐arrangement. 1 H NMR and optical rotation data of both the (2R,3R,4S)‐ trans , trans ‐ and (2S,3R,4S)‐ cis , trans ‐coprinuslactone reported by Bernardi et al .…”

Novel Lactone Chamigrene‐Derived Metabolites from Laurencia majuscula

“…An NMR spectroscopic based method with the use of Pirkle's reagent at low temperature has proved to be useful to establish the absolute configuration of structurally diverse butenolide-containing compounds; for example, diterpenes, [11] fatty acid di-γ-lactones, [12] and annonaceous butenolides. [13] Now for the first time we apply this method with success to determine the absolute configuration at the ring closure carbon atom of a γ-and δ-lactone embedded in the chamigrene network of compounds 1 and 2, respectively.…”

A novel and #947;-lactone and other constituents of a Tanzanian <i>Antidesma venosum</i>

“…The assignment of the relative stereochemistry of compound 1 was achieved using the NOESY spectrum in conjunction with the reported 13 C NMR values [18] from which the trans-trans-cis stereochemistry relationship of the lactones moiety was determined. Inspection of 13 C NMR spectrum suggest the trans configuration between C-5 methyl (δ C 18.2) and the hydroxyl group at C-4, when the methyl group is cis to hydroxyl group its 13 C NMR chemical shift is around δ C 13 and it is around δC 18 when it is trans to it [19].…”

“…Also CH 2 (δ C 28.7) at C-3 is trans to hydroxyl group at C-4, if the CH 2 is cis to hydroxyl group its signal appears at around δ C 23 and it appear at around δ C 27 if its trans to it [16]. The actual relative configuration of the γ-lactone moiety was assigned to be 3R, 4R, 5S by comparing the δC values with the literature [18][19][20][21].…”

“…From the literature search, the average values around 1 ppm (∆δ C -5 -C-4 = 1) indicate a vicinal trans relative configuration between H-5 and H-4, while the lateral side chain and the methyl group are cis with typical values being δ C 80 (C-5) and 79 (C-4) [18]. In the 13 C NMR spectrum of compound 1, the carbon signals for C-5 and C-4 were observed to resonate at δ C 80.2 and 79.1 respectively giving a difference of 1.1 ppm and confirming the relative configuration of 3R, 4R, 5S of the γ-lactone moiety.…”