Functional group changing position

Substitution of a dipeptide unit by a cychc dipeptide derivative within a peptide chain can induce certain conformational restraints that may alter the biological response via changing receptor selectivity. A facile procedure for synthesis of pyrazinone ring-containing opioid mimetics [21] has been elaborated, based on the cycHzation of readily available dipep-tidyl chloromethyl ketones [22] (Scheme 6). This method affords 2(IH)-pyrazinone derivatives containing substituents with desired functional groups at positions 3 and 6 in high yield. 

This chapter deals with a variety of reactions of steroid derivatives in which functional groups change their positions, while the steroid skeleton retains its normal structure. 

The presence and the nature of a functional group at position 12 on imine derivatives of 5a,20(N)-conene (24) changed the reactivity of the imino-group towards peracids." By the action of one mole of p-nitroperbenzoic acid on some derivatives of 5o,2(XN)-conene (24) (with various substituents at position 12), the (20R)-oxaziridine (25), the(20S)-oxaziridine(26),and the nitrone (27) were obtained... 

The effect of 17-substituents on the base-catalysed equilibration of steroidal 2j5,3y -disubstituted 6-ketones has been investigated The presence of a range of functional groups at position 17 results in marked changes in the equilibrium between 5a- and 5) -isomers and this cannot be explained in terms of conformational transmission or by simple transmission of polar effects. ... 

Docetaxel differs from paclitaxel at two positions in its chemical structure. It has a hydroxyl functional group on C-10 (see Fig. 101.1) whereas paclitaxel has an acetate ester, and a tert-butyl carbamate ester exists on the phenylpropionate side chain instead of the benzyl amide in paclitaxel. The C-10 functional group change causes docetaxel to be more water soluble than paclitaxel. 

In the second category (right side of Table 21.2), the position of the functional group changes. 

Peak Position (cm ) Intensity (ops) Peak Position (cm ) Intensity (cps) Functional Groups Change relative to virgin (Note 1)... 

Palladium oxazoline compounds (e.g., (47)) have been used to catalyze the cyclization/hydro-silylation of functionalized 1,6-dienes (Scheme 31). With R = Pr1, >95% diastereomeric excess and 87% ee was achieved at low temperature. Changing the ligand bulk with R = Bu1 gave a higher ee value, but poorer diastereoselectivity. A range of functional groups can be tolerated at both the allylic and terminal alkene positions.135-137... 

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