Abstract: A process is provided for preparing 4-alkyl- or 4-aryl-oxycarbonyl paclitaxel analogs which includes the steps of converting paclitaxel into a C-7 acylprotected paclitaxel employing an electrophilic protecting group, such as benzoyloxycarbonyl, and converting the C-7 protected analog into the 4-alkyloxycarbonyl or 4-aryloxycarbonyl paclitaxel analog. Novel intermediates produced in the process are also provided.

Abstract: Novel water soluble carbodiimides, and intermediates or derivatives thereof, such as isoureas or isothioureas, are described. A particularly preferred embodiment is bis[4-(2,2-dimethyl-1,3-dioxolyl)methyl] carbodiimide (BDDC), which can be synthesized efficiently from 1,2-isopropylideneglycerol (solketal). The isoureas are effective esterifying agents. The corresponding N-protected amino acid tert-butyl, benzyl, isopropyl, ethyl, and methyl esters can be synthesized in high yield under neutral conditions, with no urea residue after simply washing with aqueous acid. Amino acid couplings utilizing carbodiimide embodiments give peptides in good yield, free of carbodiimide by-products, after washing with dilute acid, while racemization-free peptides are also obtained.