[Structure: see text] A mild and efficient [3+2] nitrile oxide/olefin cycloaddition allows coupling of the highly functionalized naphthalene and isocoumarin hemispheres of purpuromycin. A rationale of the inability of advanced keto alcohols to spirocyclize is presented based upon a systematic examination of the electronic factors present in these systems and suggests that the biosynthesis of purpuromycin does not proceed through open-chain intermediates.

Protoplasts from 8-to 9-day-old wheat (Triticum aestivum L.) leaves were used to isolate organelles which were examined for their contents of peptide hydrolase enzymes and, in the case of vacuoles, other acid hydrolases. High yields of intact chloroplasts were obtained using both equilibrium density gradient centrifugation and velocity sedimentation centrifugation on sucrose-sorbitol gradients. Aminopeptidase activity was found to be distributed, in approximately equal proportions, between the chloroplasts and cytoplasm. Leucyltyrosine dipeptidase was mainly found in the cytoplasm, although about 27% was associated with the chloroplasts. Vacuoles shown to be free from Ceilulysin contamination contained all of the protoplast carboxypeptidase and hemoglobin-degrading activities. The acid hydrolases, phosphodiesterase, acid phosphatase, a-mannosidase, and fP-N-acetylgucosamidase were found in the vacuole to varying degrees, but no f8-glucosidase was localized in the vacuole.Studies of protein degradation in plant tissues have demonstrated the existence of a diverse group of peptide hydrolase enzymes. Protein degradation has been envisaged as a process initiated by endopeptidase action and continued through the action of exopeptidases, including aminopeptidases, carboxypeptidase, and di-and tri-peptidases to eventually release amino acids for storage and/or transport (24). Characterization of these enzymes (5,15,22,29) has shown that, despite their common role in protein breakdown, they have few similarities with respect to the conditions required for optimal in vitro activity. These differences, particularly differences in optimum assay pH, have led to suggestions of enzyme compartmentalization as a means of regulating protein degradation, since the plant cell contains a number of localized pH zones by virtue of its various organelles.Although acid proteinases are known to be localized in leaf vacuoles (3,11), no other peptide hydrolases have been reported there. Carboxypeptidase activity has been located in protein bodies from the cotyledons of germinating mung beans (7,27) and in vacuoles prepared from the endosperm tissue of 4-d-old castor bean seedlings (18) but has not been reported in vacuoles isolated from leaf tissue. In a previous publication (30), we examined the patterns of activity of a number of enzymes during senescence of the wheat plant. The present study was undertaken to examine the spatial relationship between these enzymes, which include acid proteinase, amino-and carboxypeptidases, and an alkaline dipep- MATERIALS AND METHODS Plant Material. Wheat seeds (Triticum aestivum cv. Egret) were imbibed for 24 h prior to being transferred to 34-x 29-x 6-cm trays containing a compost soil mixture. Plants were grown in a glasshouse under natural daylength and light-intensity conditions. Plants were watered daily without additional nutrients.Protoplast Preparation. Primary leaves from 8-to 9-d-old wheat seedlings were used to isolate protoplasts. The lower epidermis was removed, and the leaves wer...

The total synthesis of (-)-scabronine G has been achieved in a concise manner from the (-)-Wieland-Miescher ketone. Scabronine G and its more potent methyl ester (also prepared) display activity as nonpeptidyl inducers of nerve growth factor production.

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