abstract |
A compound having the formula (4): whereinX is oxygen or sulfur, R9 and R10 are each a hydrogen or a protecting group, and R11 is an aliphatic hydrocarbon, a -COR12 group where R12 is alkyl, aryl or alkoxy, or a group of formulawherein R5 and R6 are each hydrogen or hydroxyl, m is 1 to 4, and n is 0-2. |