temperature of the solvent stage iii the deprotection of p 4 or p u2032 4 is carried out in one or more stages and under conditions which depend on the nature of the protective groups x and if appropriate pg 1 a person skilled in the art may refer to u201c greene 39 s protective groups in organic synthesis u201d 4th edition isbn 978 0 471 69754 1 to find if appropriate these conditions thus for some protective groups for example compound p 4 with x boc the deprotection can be carried out in the presence of an organic or inorganic acid ah in this case the deprotection results in the compound p 5 in the salt form for other protective groups the deprotection can be carried out in the presence of an organic or inorganic base b in this case the deprotection results in the compound p u2032 5 in the base form the temperature of the deprotection reaction is preferably between 0 u00b0 c and 50 u00b0 c the acid can be a strong acid such as for example hydrochloric acid which results in the hydrochloride the base can be for example sodium hydroxide it is also possible to combine an acid treatment and a basic treatment in particular for p u2032 4 which comprises two different protective groups x and pg 1 stage iv if necessary the z isomer is separated from the e isomer by any purification technique known in organic synthesis it can be.