Unusual Meroterpenoids from Leaves of Psidium guajava

NMR Fingerprints of Formyl Phloroglucinol Meroterpenoids and Their Application to the Investigation of Eucalyptus gittinsii subsp. gittinsii

NMR fingerprints provide powerful tools to identify natural products in complex mixtures. Principal component analysis and machine learning using ¹H and ¹³C NMR data, alongside structural information from 180 published formyl phloroglucinols, have generated diagnostic NMR fingerprints to categorize subclasses within this group. This resulted in the reassignment of 167 NMR chemical shifts ascribed to 44 compounds. Three pyrano-diformyl phloroglucinols, euglobal In-1 and psiguadiols E and G, contained ¹H and ¹³C NMR data inconsistent with their predicted phloroglucinol subclass. Subsequent reinterpretation of their 2D NMR data combined with DFT ¹³C NMR chemical shift and ECD calculations led to their structure revisions. Direct covariance processing of HMBC data permitted ¹H resonances for individual compounds in mixtures to be associated, and analysis of their ¹H/¹³C HMBC correlations using the fingerprint tool further classified components into phloroglucinol subclasses. NMR fingerprinting HMBC data obtained for six eucalypt flower extracts identified three subclasses of pyrano-acyl-formyl phloroglucinols from Eucalyptus gittinsii subsp. gittinsii. New, eucalteretial F and (+)-eucalteretial B, and known, (-)-euglobal VII and eucalrobusone C, compounds, each belonging to predicted subclasses, were isolated and characterized. Staphylococcus aureus and Plasmodium falciparum screening revealed eucalrobusone C as the most potent antiplasmodial formyl phloroglucinol to date.

Six Unusual Meroterpenoids from the Leaves of Psidium guajava L. and Their PTP1B Inhibitory Activities

Six unusual meroterpenoids, psidiguajadiol A-J (1-6), and three known meroterpenoids (7-9) were isolated from the leaves of Psidium guajava L. Compounds 2-6 represent the first examples of 6/8-formyl-5,7-dihydroxy-4-phenylchromane-coupled sesquiterpenoids. The structures of the undescribed compounds, including their absolute configurations, were elucidated by spectroscopic analyses, X-ray diffraction, and computational calculations. Compounds 3, 4, and 6 exhibited inhibitory activities against PTP1B with IC₅₀ values of 9.83, 18.52, and 16.87 μM, respectively. In light of these findings, we performed molecular docking studies to predict their inhibition mechanisms at the atomic level.

Meroterpenoids: A Comprehensive Update Insight on Structural Diversity and Biology

Meroterpenoids are secondary metabolites formed due to mixed biosynthetic pathways which are produced in part from a terpenoid co-substrate. These mixed biosynthetically hybrid compounds are widely produced by bacteria, algae, plants, and animals. Notably amazing chemical diversity is generated among meroterpenoids via a combination of terpenoid scaffolds with polyketides, alkaloids, phenols, and amino acids. This review deals with the isolation, chemical diversity, and biological effects of 452 new meroterpenoids reported from natural sources from January 2016 to December 2020. Most of the meroterpenoids possess antimicrobial, cytotoxic, antioxidant, anti-inflammatory, antiviral, enzyme inhibitory, and immunosupressive effects.

Amino Acid Profiling Study of Psidium guajava L. Leaves as an Effective Treatment for Type 2 Diabetic Rats

Type 2 diabetes mellitus (T2DM) has become a major disease threatening human health worldwide. At present, the treatment of T2DM cannot cure diabetes and is prone to many side effects. Psidium guajava L. leaves have been reported to possess hypoglycemic activity, and they have been widely used in diabetes treatment in the folk. However, the antidiabetic mechanism has not been clearly explained. Also, the change in amino acid profile can reflect a metabolic disorder and provide insights into system-wide changes in response to physiological challenges or disease processes. The study found that P. guajava L. leaves can decrease fasting blood glucose and lipid levels in type 2 diabetic rats induced by streptozotocin. Through the analysis of amino acid profiling following 20 days of gavage administration, the concentration data were modeled by principal component analysis and orthogonal partial least squares discriminant analysis to find the different metabolites and related metabolic pathways (including cysteine and methionine metabolism, valine, leucine, and isoleucine biosynthesis, phenylalanine, tyrosine, and tryptophan biosynthesis) for the explanation of the hypoglycemic mechanism of P. guajava L., which provides an experimental and theoretical basis for diabetes prediction and for the development of new drugs for the treatment of diabetes.