Benzoate 2- azido

The Staudinger-aza-Wittig cyclization methodology for imine formation can also be applied to the synthesis of oxazolines under essentially neutral conditions.Thus, an azido ester such as 281 reacts with triphenylphosphine to give the oxazoline 283 in excellent yield. There was no evidence for cychzation at the benzoate presumably because cyclization to a five-membered ring is faster than... 

The facile formation of the iodo compound, and the subsequent reduction with tributyltin hydride opens a new access to 2-amino-2,3-dideoxy-D-glucose (D-lividosamine) present in various aminoglycoside antibiotics [92], The same strategy been used in the synthesis of C-lO -C-l fragment of boromycin [93]. Displacement of the C-3 imidazylate ester of a 2-azido-2-deoxy-a-D-altropyranose derivative with benzoate occurred readily [94], compared with the corresponding tosylate [95],... 

The reaction in Scheme 3 for HOR = HODhbt is accompanied by a side reaction giving rise to the formation of oxobenzotriazinyl 2-azidobenzoate 50 (Scheme 10). ] The 2-azido-benzoate originates from reaction of HODhbt (48) with addition product 49 formed by reaction of the carbodiimide with 48. It is detectable by HPLC and by the azide absorbance at 2120 cm" in the IR spectrum. It is an acylating agent and thus causes chain termination if left as a contaminant of the ester. The side reaction is completely eliminated by allowing a 5-minute activation time before addition of the hydroxy compound.0 5 l... 

Modification at the C-2 position also exhibits interesting effects on the cytotoxicity. Compound 8c, which is an SB-T-3002 analog with the addition of a fluorine at the j ara-position of the C-2 benzoate, has weaker activity than that of docetaxel but similar to that of paclitaxel. Difluoro-paclitaxel 8e showed drastically weaker cytotoxicity. 2-(3,5-Difluorobenzoyl)taxoid 8f was one of the most active analogs, showing that substitution at the meto-position is tolerated very well. These results are consistent with other reports that substitution at the para-position of the C-2 benzoate (cyano, chloro, methoxy, and azido) significantly decreases the activity but w6 a-substitution enhances activity (23). 

---