Absolute Configuration of (13R)- and (13S)‑Labdane Diterpenes Coexisting in Ageratina jocotepecana

• Published in: Journal of natural products (Washington, D.C.) D.C.), 2014-04, Vol.77 (4), p.1005-1012
• Main Authors: García-Sánchez, Edgar, Ramírez-López, César B, Talavera-Alemán, Armando, León-Hernández, Alejandra, Martínez-Muñoz, Rosa E, Martínez-Pacheco, Mauro M, Gómez-Hurtado, Mario A, Cerda-García-Rojas, Carlos M, Joseph-Nathan, Pedro, del Río, Rosa E
• Format: Article
• Language: English
• Subjects: Ageratina - chemistry; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - isolation & purification; Anti-Bacterial Agents - pharmacology; Bacillus subtilis - drug effects; Circular Dichroism; Diterpenes - chemistry; Diterpenes - isolation & purification; Diterpenes - pharmacology; Mexico; Microbial Sensitivity Tests; Models, Molecular; Molecular Structure; Staphylococcus aureus - drug effects; Stereoisomerism
• ISSN: 0163-3864; 1520-6025
• DOI: 10.1021/np500022w

Chemical investigation of the hexanes extracts of Ageratina jocotepecana afforded (−)-(5S,9S,10S,13S)-labd-7-en-15-oic acid (1), methyl (−)-(5S,9S,10S,13S)-labd-7-en-15-oate (2), (+)-(5S,8R,9R,10S,13R)-8-hydroxylabdan-15-oic acid (3), and (−)-(5S,9S,10S,13Z)-labda-7,13-dien-15-oic acid (5). The coexistence of (13R)- and (13S)-labdanes in this member of the Asteraceae family was demonstrated by vibration circular dichroism measurements of ester 2 and methyl (+)-(5S,8R,9R,10S,13R)-8-hydroxylabdan-15-oate (4) in comparison to the DFT B3LYP/DGDZVP-calculated spectra. In addition, transformation of 1 and 3 with HClO4 in MeOH yielded epimeric methyl (+)-(5S,10S,13S)-labd-8-en-15-oate (6) and methyl (+)-(5S,10S,13R)-labd-8-en-15-oate (7), respectively, confirming the presence of C-13 epimers in this plant. Diterpene 1 showed remarkable antibacterial activity against Bacillus subtilis (MIC 0.15 mg/mL) and Staphylococcus aureus (MIC 0.78 mg/mL), while diterpene 3 exhibited moderate activities against the same organisms.