Synopsis
111 this paper we have successfully applied the dicyclohexylcarbodiimide aiid the acylazide coiipliiig methods to t.he syrithesis of a series of I,-isoleuciiie peptides from dimer to octamer. In the course of o m syiithetic approavh we employed t-brit.ylo as the N-protecting and methyl ester as the C-protecting end groups. I'eptide coupliiig reactions krwwii to give products of high optical piirity in gi)od yields were used in these researches. Filially, we descsiibed pre1iniiii:ii.y st ereoc~hemical iiivestigat.ions on these homo-oligopeptides using polarinieiric und ri1tr:iviolet :ibsorptioii techniques. The conformational properties of high nioleci11:tr weight poly-a-amiiio :icids have attracted considerable att,eiition :is proteiii model coinpoiiiids. 111 addition, iiivestigatioiis performed on oligopeptides h:ive yielded important iiiforinatioii coiiceriiiiig the depeiidence of secondary st,rrictiii.e on chaiii leiigth. (;oodm:iii :tiid (:o-~orkei~s*-~ have cwnducted exterisive st,iidies on the criticnl size for helix format ion iii L-alaiiitie, r,-:ispart,ate and Lglutamate oligoinei,s and cooligoiiiers. 13y :t v;iriely of techtiiqries, they dernonst rated that the oiiset of secoiid:try striictiire i h depeiideiit h i 1 1 o n the solvent :riid t,he iiitture of the side ch:tiii. III this :md i i i the :ic~coriil)aii~iiig6 paper we report the esteiisioii of this itppro:tch t o hoiiio-o1igopel)tides derived f r o m i,-isoleiicine, which is coilsidered to be disriiptive of a-helices for steric i~e:tsi)iis7 i i i pn)leiiis itiid polypeptides. 111 particiihr this niairiiscript will describe the syiithesis o f the hoinologoiis series of BOC-I,-(Ileu),l-O;\Ie* (11 = 2-5) and pre1imiii:wy stereoc*heniic:il iiivestig:it.ions by rneaiis of polarimetry a i d ultraviolet (UV) spectroscopy. Iii 1 he :icconipmying p p e r i i rniich more detailed analysis of the stereochemistry of thehe oligopept ides will Iir reported.