A ´lvarez-Corral et al. Scheme 9. Silver-Catalyzed Cyclization of O-Propargyl Carbamates Scheme 10. Synthesis of γ-Alkylidene-γ-butyrolactams Scheme 11. Silve-Catalyzed Rearrangement of 2-(Propargylamino)benzoxazoles, Benzothiazoles, and Benzoselenazoles into Dihydropyrimidines Scheme 12. Different Examples of the Use of Imines in the Syntheses of N-Heterocycles Scheme 13. Proposed Mechanism for Silver-Promoted Cyclization of Homopropargylamines and Synthesis of the Pyrrole Crispine A

Among the phytoalexins with the highest antifungal activity is the isoflavonoid based group of pterocarpans. Here, we present a comprehensive inventory of the structures and sources of pterocarpans, and summarize some of their most interesting biological activities.

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The contents of oxalic acid and calcium in several wild edible plants were analyzed. Oxalic acid was determined by an espectrophotometric method based on the decrease of absorbance at 335 nm due to the dissociation of the zirconium(IV)−chloranilate complex, consecutive to the addition of oxalic acid. Calcium was determined by atomic absorption spectroscopy. The results show the absence of this acid in two of the studied plants:  hoary cress (Cardaria draba (L.) Desv.) and vervain (Verbena officinalis L.). Also noticeable is the high content of oxalic acid in goosefoot (Chenopodium album L.), with a range of values from 360 to 2000 mg/100 g of fresh weight, and the high ratio (oxalic acid/calcium) in curly dock (Rumex crispus L.), with a mean value of 32. Keywords: Oxalic acid; calcium; antinutritive substance; wild edible plants