[[9-[(9-Fluorenylmethyloxycarbonyl)amino]xanthen-2(or 3)-yl]oxy]alkanoic acid (XAL) handles have been prepared by efficient four-step routes from 2- or 3-hydroxyxanthone and coupled onto a range of amino-functionalized supports. The resultant XAL supports are the starting points for solid-phase peptide synthesis by Fmoc chemistry. Upon completion of chain assembly, C-terminal peptide amides are released in excellent yields and purities by use of low concentrations [1-5% (v/v)] of trifluoroacetic acid (TFA) in dichloromethane, often without a need for added carbocation scavengers. These cleavage conditions allow retention of all or a significant portion of tert-butyl type and related side-chain protecting groups, which subsequently may be removed fully in a solution process carried out at higher acid concentration. XAL supports are particularly useful for the synthesis of acid-sensitive peptides, including tryptophan-containing sequences that are known to be susceptible to yield- and/or purity-reducing alkylation side reactions. The effectiveness of this chemistry was shown with the syntheses of prothrombin (1-9), acyl carrier protein (65-74), Tabanus atratus adipokinetic hormone, fragments of the protein RHK 1, CCK-8 sulfate, and oxytocin. Furthermore, the application of XAL supports for the preparation of fully protected peptide amides has been demonstrated.

SYNOPSISa,w-Divinyl-terminated polydimethylsiloxane polymers with low polydispersivity were synthesized via anionic polymerization of hexamethylcyclotrisiloxane ( D3). Five "monodisperse" polymers with different molecular weights were hydrosilylated with tetrakisdimethylsiloxysilane in the presence of platinum catalysts and inhibitors to form crosslinked networks. Control studies to determine the effect of platinum, silicon hydride, and heat were performed to verify that no redistribution occurred during hydrosilylation. The properties of these cured samples were characterized chemically by degradation with trifluoromethanesulfonic acid in the presence of hexamethyldisiloxane, infrared spectroscopy, and nuclear magnetic spectroscopy. Mechanical properties were studied by measurements of Shore A hardness, dynamic shear modulus, and tensile modulus. The relationship between the molecular weight of the vinyl polymer and the final properties of the cured networks was measured. 0 1993 John Wiley & Sons, Inc.

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