NOVELTY - Making (P1) Latanoprost (I) involves reacting (3aR,4R,5R,6aS)-4-((3R)-3-hydroxy-5-phenylpentyl)-5-(triethylsilyloxy) hexahydro-2H-cyclopenta(b)furan-2-ol with (4-carboxy butyl)triphenyl phosphonium bromide in presence of suitable base in suitable solvent, followed by treatment with suitable acid to provide (Z)-7-((1R,2R,3R,5S)-3,5-dihydroxy-2-((3R)-3-hydroxy-5-phenylpentyl) cyclopentyl)hept-5-enoic acid (VI), and reacting the compound (VI) in-situ with 2-halopropane in presence of suitable base in suitable solvent to provide the compound (I).    USE - For the preparation of isopropyl (Z)-7((1R,2R,3R,5S)-3,5-dihydroxy-2-((3R)-3-hydroxy-5-phenylpentyl)cyclopentyl)-5-heptenoate (claimed) which is used to control the progression of glaucoma or ocular hypertension by reducing intraocular pressure.    ADVANTAGE - The process is cost-effective, time saving and environmental friendly process; provides Latanoprost with high yield and purity in shorter reaction time; avoids the use of protecting groups which are sensitive towards mild acid, base, reduction and chromatographic purification on silica gel; and avoids the use of additional reagents and solvents for the repeated protection and deprotection processes.    DETAILED DESCRIPTION - Preparation (P1) of isopropyl (Z)-7((1R,2R,3R,5S)-3,5-dihydroxy-2-((3R)-3-hydroxy-5-phenylpentyl)cyclopentyl)-5-heptenoate (i.e. Latanoprost) (I) either involves a) reacting (3aR,4R,5R,6aS)-4-((3R)-3-hydroxy-5-phenylpentyl)-5-(triethylsilyloxy) hexahydro-2H-cyclopenta(b)furan-2-ol (IV) with (4-carboxy butyl)triphenyl phosphonium bromide (V) in presence of a suitable base in a suitable solvent, followed by treatment with a suitable acid to provide (Z)-7-((1R,2R,3R,5S)-3,5-dihydroxy-2-((3R)-3-hydroxy-5-phenylpentyl) cyclopentyl)hept-5-enoic acid (VI), and b) reacting the compound (VI) in-situ with 2-halopropane in presence of a suitable base in a suitable solvent to provide the compound (I); or a1) reducing the C-C double bond of (3aR,4R,5R,6aS)-4-((3S,1E)-3-hydroxy-5-phenylpent-1-enyl)-5-(triethylsilyloxy)hexahydro-2H-cyclopenta(b)furan-2-one (II) with a metal catalyst in a suitable solvent under hydrogen pressure to provide (3aR,4R,5R,6aS)-4-((3R)-3-hydroxy-5-phenylpentyl)-5-(triethyl silyloxy)hexahydro-2H-cyclopenta(b)furan-2-one (III), b1) reducing the keto group of the compound (III) with a suitable reducing agent in a suitable solvent to provide the compound (IV), c1) reacting the compound (IV) with the compound (V) in presence of a suitable base in a suitable solvent, followed by treatment with a suitable acid to provide the compound (VI), and then performing step (b). INDEPENDENT CLAIMS are included for the following:    (1) new intermediates of (III) and (IV) or their isomers;    (2) preparing (P2) the compound (III) involving performing the step (a1) to provide the compound (III);    (3) preparing (P3) the compound (IV) involving performing the step (b1) to provide the compound (IV);    (4) preparing the compound (VI) involving performing the step (c1).