Synthesis and Structural Modifications

It is now well-established that unsymmetrical substituted menthylphosphinates, RR P(0)0Men, as well as the corresponding phosphine-boranes RR P(BH3)OMen and phosphinothioates RR P(S)OMen, can be separated readily into the di-astereomeric forms, and subsequently reacted with Grignard reagents to afford P-chirogenic tertiary phosphines with a high degree of stereospecificity [57]. The 

Phosphine-borane 63a (75% ee) was obtained by reduction of compound (Sp)-62a using LDBB at -60°C and nucleophilic substitution with iodomethane in 72 % yield. The observed loss of optical purity may be ascribed to stereomutation of the generated tricoordinated phosphorus species. Recrystallization afforded (S)-63a in 99% ee. On the other hand, severe racemization was observed using the same method with (Rp)-62b. An alternative strategy consisted of deborana-tion of (Rp)-62b using ZSl-methylpyrrolidine, methylation with methyl triflate. 

In conclusion, the potential of optically active menthylphosphino compounds is vast since the OMen group may be substituted for aryl-, alkyl substituents, or even the H atom. In particular, replacement by a methyl group and H enables one to obtain key intermediates which have been found to be extremely important in the synthesis of other substituted monophosphines or diphosphines, as will be shown in the sections which follow. 

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Structural variants of porphyrins obtained by heterocyclic core modification, macrocyclic ring expansion, alteration of structural topology, and incorporation of tailor-made substituents constitute an area of considerable interest. Potentially rich families of conjugated heteroporphyrins with well-defined structures provide an opportunity for implementation in applications in the field of chemistry, biology, and material science. This chapter reports on the synthesis and structural modifications of a number of heteroporphyrins. 

These results indicated that clinical PA isolates from various infections display marked heterogeneity with respect to the acylation state of their lipid A, reflecting differences in selective pressure that these infections impose on PA lipid A synthesis and structural modifications. Further study of the synthesis and regulation of lipid A modifications that are associated with CF lung disease is needed to understand their role in antibiotic resistance and other adaptations that are relevant to this specialized niche. 

Synthesis and structure modification of unsymmetrically substituted phthalocyanines 07UK732. 

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