A mild and general solid-phase method for the synthesis of chiral polyamines. Solution studies on the cleavage of borane-amine intermediates from the reduction of secondary amides.

A mild oxidative workup protocol using iodine in an acetic acid-acetate buffer solution is described for the cleavage of borane-amine adducts arising from the borane-promoted reduction of polyamides supported onto practical trityl-based resins. Chiral polyamines with diverse side-chain functionalities can be generated as free bases without premature release from the solid support and with essentially no racemization using this method. A series of model oligomeric secondary diamides 6 containing various alpha-amino acid residues (Val, Phe, Tyr, Ser, Cys, Met, Gln, Trp) provided triamine products 8 in high yields and good to excellent purity. On the other hand, a substrate containing a tertiary amide (15) formed a rather unusual triaminoborane intermediate that required more stringent workup conditions to liberate the polyamine product 20. The reduction of oligomeric tertiary amides such as 9 was found sluggish, but these compounds could nonetheless be obtained in high purity from in situ reductive amination of the corresponding secondary amines. Control studies, carried out in solution with model secondary amide 23, confirmed the efficiency of the buffered iodine solution and highlighted several advantages (no heating necessary, no need for strong bases or acids) over existing methods for the cleavage of borane-amine adducts. A possible mechanism involving all buffer components (iodine, acetic acid, and acetate ion) is proposed in which borane-amine adducts are transformed first to the monoiodoborane-amine and then to the corresponding acetoxyborane-amine adduct of much weaker coordination affinity. The latter would dissociate readily and get trapped by the acetic acid to provide the desired secondary amine. This reduction/oxidative workup protocol is useful as a general method for the facile solid-phase synthesis of polyamines for eventual release in solution and use in various applications. It is also potentially very useful toward the synthesis and screening of bead-supported libraries of free oligoamines assembled through split-pool methods.

Solid phase syntheses of polyamine toxins HO-416b and PhTX-433. Use of an efficient polyamide reduction strategy that facilitates access to branched analogues.

[structure--se text] Polyamine toxins HO-416b (1) and PhTX-433 (2) isolated from the venom of insects are important lead compounds in neuropharmacology. Their total synthesis has been achieved on a trityl derivatized resin in good yield and purity using a mild borane reduction protocol to access the polyamine chains from polyamide precursors. The synthesis of PhTX isomer 3 demonstrates the potential of this strategy for the generation of branched analogues.

Chemoenzymatic synthesis of a trimeric ganglioside GM3 analogue.

A trimeric beta-lactosyl cluster based on 2-nitro-2-(hydroxymethyl)propane-1,3-diol was prepared using the trichloroacetimidate method. Kinetic studies showed that this cluster was an effective acceptor for rat-liver alpha-(2-->3)-sialyltransferase. Its KM was comparable to those for monomeric lactose and N-acetyllactosamine acceptors, and its Vmax was 1% of that measured for the LacNAc acceptor. Preparative-scale sialylation using this enzyme afforded a trimeric cluster of the ganglioside GM3 oligosaccharide in good yield. The NMR spectra of the trimeric GM3 analogue suggest that the oligosaccharide conformation is not significantly perturbed by this level of clustering.

Trabeculectomy versus Scheie's operation: a comparative retrospective study in open-angle glaucoma in Kenyans.

A comparative retrospective study was performed on 39 patients with open-angle glaucoma in whom the right eye was subjected to Scheie's operation, the left to trabeculectomy. Trabeculectomy without the use of additional therapy or reoperation brought the intraocular pressure to under 22 mmHg in 80% of the cases compared with 74% treated by Scheie's operation. Reduction of visual acuity postoperatively was 4 times more frequent with Scheie's operation than with trabeculectomy. A report on a second group of patients in whom 47 trabeculectomies were performed is also given.