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1 5-Lipoxygenase (5-LOX) products from endogenous arachidonic acid in ionophore-stimulated peritoneal polymorphonuclear leukocytes (PMNL) and from exogenous substrate (20 gM) in 105,000 g supernatants were measured. 2 The effects of natural pentacyclic triterpenes and their derivatives on 5-LOX activity were compared with the inhibitory action of acetyl-l -keto-p-boswellic acid (AKBA), which has been previously shown to inhibit the 5-LOX by a selective, enzyme-directed, non-redox and non-competitive mechanism. 3 The 5-LOX inhibitory potency of AKBA was only slightly diminished by deacetylation of the acetoxy group or reduction of the carboxyl function to alcohol in intact cells (ICs = 1.5 vs. 3 and 4.5 pM, respectively) and in the cell-free system (8 vs. 20 and 45 gM).5 fl-Boswellic acid (f-BA), lacking the 1 1-keto function, inhibited 5-LOX only partially and incompletely, whereas the corresponding alcohol from fl-BA, as well as amyrin, acetyl-ll-keto-amyrin, 1 l-keto-f-boswellic acid methyl ester had no 5-LOX inhibitory activity up to 50 pM in either system. 5 fl-BA only partially prevented the AKBA-induced 5-LOX inhibition, whereas the non-inhibitory compounds, amyrin and acetyl-1 l-keto-amyrin, almost totally antagonized the AKBA effect and shifted the concentration-inhibition curve for the incomplete inhibitor fl-BA to the right. In contrast, the noninhibitory 1 1-keto-fl-BA methyl ester exerted no antagonizing effect.6 The results demonstrate that the pentacyclic triterpene ring system is crucial for binding to the highly selective effector site, whereas functional groups (especially the 11 -keto function in addition to a hydrophilic group on C4 of ring A) are essential for 5-LOX inhibitory activity.

The previously reported reaction of phthalocyanines [H2(pc)] with PBr3, which was claimed to give a phosphorus(III) phthalocyanine “(PcPIII)”, has been reinvestigated in detail with both unsubstituted and alkyl‐substituted phthalocyanines, 1‐4. The products exhibit unusual electronic and mass spectra compared to normal phthalocyanines and have been identified as oxophosphorus(V) triazatetrabenzcorroles 5–8. The corresponding dihydroxyphosphorus(V) phthalocyanine hydroxides 9–12 have also been synthesized for the first time by insertion of phosphorus(V) into phthalocyanines and have been characterized in detail. The different reactivities of PBr3 and POX3 (X = Cl, Br) toward phthalocyanines are discussed.

Tetra-tert-butylphthalocyaninatonickel is synthesized from phthalic anhydride as well as from phthalodinitrile and nickel chloride, whereby a mixture of four different structural isomers are obtained; two of these isomers, with C2"and C,-symmetry are isolated for the first time by HPLC and medium pressure liquid chromatography (MPLC) and characterized.

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