commercial sources and used without further purification. H-His (Trt)-2-Cl-Trt
resin and H-Val-2-Cl-Trt resin were purchased from AAPPTEC (Louisville,
KY). Boc-L-alanine, Fmoc-L-alanine, Nα-Fmoc-Nω-(2,2,4,6,7-pentamethyldihydro-benzofuran-5-sulfonyl)-
hydrochloride, Fmoc-L-isoleucine, Fmoc-O-tert-butyl-L-tyrosine, Fmoc-L-proline,
Fmoc-6-aminohexanoic acid, 4-aminobenzyl alcohol (PABA), O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium
hexafluorophosphate (HATU),N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline(EEDQ),N,N′-diisopropylethylamine
(DIPEA), trifluoroacetic acid (TFA), and piperidine were purchased
from Chem Impex (Wood Dale, IL). 7-Ethyl-10-hydroxycamptothecin (SN-38)
was purchased from Biosynth (San Diego, CA). N,N-dimethylformamide
(DMF), dichloromethane (DCM), methanol (MeOH), tetrahydrofuran (THF),
acetonitrile (ACN), ethyl acetate (EtOAc), hexane, triisopropylsilane
(TIPS), phosphorus tribromide, diethyl ether (Et2O), silica
gel, 18-crown-6, and potassium carbonate were purchased from Sigma-Aldrich
(Burlington, MA). N3-PEG4-acid, Fmoc-N-amido-PEG3-acid, and DBCO-C6-acid were purchased from BroadPharm
(San Diego, CA).