In order to improve the water solubility of nonpolar compounds such as drugs or dyes, new amphiphilic molecules are needed. In this paper we describe a new class of triblock amphiphiles that we have synthesized by a straightforward convergent approach. These amphiphiles each consist of a nonpolar biphenyl core and a polar shell based on various generations of monoamino polyglycerol dendrons, coupled to the core through amide linkages (1). For the synthesis of these monoamino dendrons we applied a simple iterative two‐step process based on allylation of an alcohol group and catalytic dihydroxylation. As starting materials, D,L‐serine/serinol and – in a second, similar pathway – commercially available triglycerol were used. The transport behavior of these defined triblock amphiphiles was then investigated with the nonpolar dye Nile Red in water.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

No abstract

No abstract

The synthesis of optically active b-benzyl-g-butyrolactones from butynediol via four transition metal catalysed reactions is reported. Key reactions are the hitherto unknown enantioselective hydrogenation of 2-benzyl-2-buten-1,4-diols using Ir(I)-phosphinooxazoline catalysts and the regiocontrolled oxidation of the resulting 2-benzyl-1,4-butanediols to the b-substituted butyrolactones.Key words: (+)-b-benzyl g-butyrolactones, butynediol, enantioselective hydrogenation Butyrolactone lignans 1 3 are an important class of natural products possessing notable biological activities, in particular antiviral, 4 cytotoxic 5 and canceroprotective 6 properties. We have recently reported a short synthesis of racemic butyrolactone lignans 1 via a-alkylation of b-substituted butyrolactones 2 (Scheme 1). 7 These lactone intermediates were prepared by Raney-Nickel or Pd/C catalysed hydrogenation of the corresponding unsaturated lactones 3, which were obtained from butynediol 4 in three transition metal catalysed reactions. 7 Scheme 1 Retrosynthesis of lactone lignans 1Since natural lignans 1 are generally non-racemic, an asymmetric hydrogenation of 3a-d to 2a-d using chiral catalysts was envisioned to provide optically active lignans and analogs (Scheme 2). Transition metal catalysed asymmetric hydrogenation of b-or g-methylene butyrolactones have been described. 8 However, we observed that butenolides 3a-d gave poor conversions upon homogeneous hydrogenation in the presence of chiral catalysts (Table 1). Thus, butenolides 3a,b were converted to lactones 2a,b in about 20% and 12% ee (2 h, 100 bar H 2 ) using Ir(I)-phosphinooxazoline catalyst A 9 (Table 1, entries 1 and 3). The conversion was 58% after 18 hours while the ee remaining low at 12% (entry 2). Similarly, reduction of 3b or 3d in presence of R-(+)-BINAP-Ru(II) 10 (120 h, 20-30 bar) afforded lactones 2b and 2d in 55 and 95% conversion, again with low ee (entries 4 and 5). 11It was reported that yeast reduction of butenolides afforded the corresponding lactones with good ee. 12 In our case, substrate 3c was reduced by yeast in the presence 12 or in the absence 13 of saccharose. The conversion of 3c to lactone 2c was 20% in each instance and the product was obtained as a racemic mixture (entries 6 and 7). Scheme 2 Attempted enantioselective reductions of lactones 3a-dSince neither asymmetric hydrogenation nor yeast reduction gave lactones 2 in acceptable yields and enantioselectivities, a different synthetic strategy was necessary. Thus, lactones 2 should be obtained by regioselective TPAP oxidation of optically active diols 5, prepared by asymmetric hydrogenation of butenediols 6 (Scheme 3).Scheme 3 New strategy for the preparation of optically active lactones 2

Conventional treatment of retinal detachment with laser and/or triamcinolon acetonide (TAAC) does not prevent loss of vision in all patients. Therefore, the development of degradable hydrogel patches covering retinal breaks was envisioned as alternative. Stable hydrogels could be formed by crosslinking hyaluronic acid with 1,2,3,4‐diepoxybutane. Triamcinolone was diffusible in the gels. The hydrogels were slowly degrading, and mass loss during hydrolytic degradation was observed starting after three weeks. The sterilized gels showed excellent intraocular biocompatibility in vivo in rabbit eyes when applied as a patch on the retina. The good retinal adherence of the patch and absence of cellular growth and proliferation in and around the gel indicated the suitability as a material for a retinal patch to prevent cell‐migration and proliferation after a retinal break and for local drug application.