Alkenyl-5,6-dihydro-a-pyrones

The antibiotic phomalactone (50) has been obtained from a Drechslera species (62) and the fungus Hirsutella thompsonii var. synnematosa (63) and found to be active against a wide range of microorganisms. Phomalactone acetate (51) has been synthesized from 2-furylcarbinols (64, 65). The absolute stereochemistry of (+)-asperlin 

Structurally related compounds hypurticin (60) and synparvolide B (61) have been isolated from yet another Hyptis species, H. urticoides, and Syncolostemon parviflorus, respectively (82, 83). The structures of (60) and (61) were determined spectroscopically with the stereochemistry of (61) being derived from its biosynthetic relationship to synparvolide A (70). 

Olguine (68) has been known for many years (7) and 5 -epiolguine 

Collett has isolated five closely related compounds, synargentolides A-E (75-79), from Syncolostemon argenteus and assigned their structures using CD and NMR techniques (85). Synargentolide D (77) was thermally unstable and paucity of material prevented stereochemical investigations. Synargentolide B (76) is epimeric at C-5 with (65). 

Compound (80), a structural isomer of umuravarumbolide (55), is a minor constituent of Cryptocarya latifolia 89). The immunosuppressive agent, (—)-PA-48153 (81), has been isolated from Streptomyces prunicolor sp. PA 48153 (90). The same compound, obtained from Streptomyces sp. NK10958 and shown to be a plant growth regulator, has been named pironetin, and the structure based on spectral data, confirmed by X-ray analysis 91, 92) and synthesis 93). 

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