The new intermediates of the present invention are the compounds of general formula I hereinafter depicted wherein R represents a straight- or branched-chain alkyl group containing from 1 to about 4 carbon atoms, preferably methyl or isopropyl, R 2

represents an acid-labile protecting group, preferably a triphenylmethyl group, and X represents a halogen, preferably bromine or iodine, atom.

The compounds of formula I are key intermediates in a new reaction sequence which permits the stereospecific preparation of analogues of mevalonic acid without the necessity to use potentially hazardous mercury compounds employed in previously known processes described, for example, by Rosen et a_l, J. Org. Che ., 1984, 49, 3994-4003 and Corey et al, J. Am. Chem. Soc, 1980, 102, 1439.

The said analogues of mevalonic acid are valuable pharmaceutically active compounds, more especially competitive inhibitors of 3-hydroxy-3-

methylglutaryl coenzyme A reductase, and are consequently inhibitors of cholesterol biosynthesis and as a result are of use in the prevention or treatment of hypercholesterolaemic and hyperlipoproteinaemic states, atherosclerosis and associated conditions.

Examples of such mevalonic acid analogues are described, for example, in the specifications of our granted South African Patents Nos. 88/5852 and 89/0645 and of their equivalents in other countries, for example United States Patent Applications Nos.- 07/230038 and 07/302389.

According to a feature of the present invention, compounds of formula I are prepared by the reaction of compounds of general formula II hereinafter depicted,

2 wherein R is as hereinbefore defined, with a halogenating agent, e.g. N-iodosuccinimide when X represents iodine and N-bromosuccinimide when represents bromine, and the appropriate alcohol of the general formula:-

R ¹ OH III wherein R is as hereinbefore defined. The alcohol of formula III may act as the solvent medium alone or with one or more additional solvents such as polar aprotic solvents, e.g. acetonitrile.

According to a further feature of the present invention, the compounds of formula I are then hydrogenated , using a hydrogenation catalyst such as palladium on charcoal or Raney nickel, in the presence of a base, for example triethylamine or an alkali metal hydroxide, e.g. potassium hydroxide, to form compounds of general formula IV hereinafter depicted, wherein R

2 and R are as hereinbefore defined.

The hydrogenation is preferably carried out in an organic solvent, for example a lower alka _. nol containing up to about 3 carbon atoms, e.g. methanol or ethanol, especially when an alkali metal hydroxide is used as the base, a lower ester, e.g. methyl or ethyl acetate, or an aromatic solvent, e.g. toluene, at about 10-60 ^β C, preferably 20-50°C and preferably at about 40-60p.s.i.

According to a further feature of the present invention, compounds of formula IV are elaborated to prepare the said mevalonic acid analogues, by the application or adaptation of known methods.

Compounds of formula II may be prepared by the application or adaptation of known methods, for example as described by Fraser-Reid et al. Can. J. Chem., 51, 3950 (1973).

The following Examples illustrate the present invention.

Nuclear Magnetic Resonance (NMR) spectra are conducted in solution in CDC1- and the chemical shifts are given in ppm with tetra ethylsilane as reference.

The following abbreviations are used:- "s" means

"singlet", "d" means "doublet", "g" means "quadruplet" and "m" means "multiplet".

EXAMPLE 1 A stirred solution of 3α,4β-dihydroxy-2β- triphenylmethoxymethyl-3,4-dihydropyran (5g) in methanol (50ml) at 0°C. was treated with N-iodo- succinimide (4.4g) during 15 minutes, maintaining the temperature at 0 to 5°C. , and the resulting solution was stirred for a further period of 90 minutes, still maintaining the temperature at 0 to 5°C. It was then allowed to warm up overnight. The mixture was evaporated to dryness under vacuum at 40°C. The residue was treated with dichloromethane (50ml) and water (30ml) and then treated slowly with solid sodium thiosulphate (ca. lg) until the mixture was decolourised. The organic layer was separated off, washed with water OO W, dried over magnesium sulphate, and evaporated to dryness, to give 3α,4β-dihydroxy-5β-iodo-6α-methoxy-2β-triphenyl

methoxy ethyltetrahydropyran (6.19g), m.p. 78-82°C.

[NMR:- s,1.57; d,2.39; d,2.42; S,2.76; s,3.36; m,3.37-3.50; d,4.46; s,5.09; m,7.20-7.35; m,7.45-7.50] .

EXAMPLE 2

By proceeding in a manner similar to that hereinbefore described in Example 1, but replacing the methanol by a mixture of acetonitrile (50ml) and methanol (lg), there was obtained 3α,4β-dihydroxy-5β- iodo-6α-methoxy-2β-triphenylmethoxymethyltetrahydro- pyran (5.80g), m.p. 79-83°C. [NMR:- s,1.58; is,2.76; S,2.80; s,3.36; m,3.37-3.50; s,3.46; m,7.20-7.35; m,7.45-7.50].

EXAMPLE 3

By proceeding in a manner similar to that hereinbefore described in Example 1, but replacing the methanol by isopropanol (50ml), there was prepared 3α,4β-dihγdroxy-5β-iodo-6α-isopropoxy-2β-triphenyl- methoxymethyltetrahydropyran (6.69g), m.p. 125-129°C. [NMR:- d,1.13; d,1.18; S,1.57; d,2.36; d,2.47; s,2.76; m,3.37-3.50; s,5.30; m,7.20-7.35; m,7.45-7.50].

EXAMPLE 4

By proceeding in a manner similar to that hereinbefore described in Example 2, but replacing the methanol by isopropanol (2g), there was prepared

3α,4β-dihydroxy-5β-iodo-6α-isopropoxy-2β-triphenyl- methoxy ethyltetrahydropyran (5.51g), m.p. 123-127°C. [NMR:- d,1.18; d,1.21; s,1.58; s,2.76; ε,2.80; m,3.37-3.50; s,3.41; q,4.31; m,7.20-7.35; m,7.45-7.50j .

EXAMPLE 5

By again proceeding in a manner similar to that hereinbefore described in Example 2, but replacing the N-iodosuccinimide by N-bromosuccinimide (3.1g), there was prepared 3α,4β-dihydroxy-5β-bromo-6α-methoxy-2β- triphenylmethoxymethyltetrahydropyran (5.23g), m.p. 92-96°C. [NMR:- s,1.57; d,2.39; d,2.41; S,2.76; s,3.36; m,3.37-3.50; s,5.09; m,7.20-7.35; m,7.45-7.50].

EXAMPLE 6

By proceeding in a manner similar to that hereinbefore described in Example 4, but replacing the N-iodosuccinimide by N-bromosuccinimide (3.1g), there was prepared 3α,4β-dihydroxy-5β-bromo-6α-isopropoxy-2β- triphenylmethoxymethyltetrahydropyran (5.72g), m.p. 99-103°C. [NMR:- d,0.85; d,l.ll; s,1.57; d,2.39; d,2.41; s,2.76; m,3.37-3.50; m,7.20-7.35; m,7. 5-7.50].

EXAMPLE 7

A solution of 3α,4β-dihydroxy-5β-iodo-6α- methoxy-2β-triphenylmethoxymethyltetrahydropyran (5.4g) in ethyl acetate (100ml) was treated with triethylamine (2ml) and damp Raney nickel paste (Ig). The mixture

was shaken in a hydrogen atmosphere at 40 psig for 21.5 hours at the ambient temperature. The catalyst was then filtered off and washed with ethyl acetate

(100ml). The combined solutions were washed with water (50ml) and evaporated to dryness, to give

3α,4β-dihydroxy-6α-methoxy-2β-triphenylmethoxymethyl- tetrahydropyran (3.83g), m.p. 136-140°C.

[NMR:- S,1.59; d,1.63; d,1.67; q,2.12; d,2.41; d,2.70; s,3.30; ,3.35-3.45; m,3.57-3.63; d,4.46; d,4.78; m,7.20-7.35; m,7.45-7.50] .

EXAMPLE 8

A solution of 3α,4β-dihydroxy-5β-iodo-6α- methoxy-2β-triphenylmethoxymethyltetrahydropyran (5. g) in ethyl acetate (100ml) was treated with triethylamine

(2ml) and damp palladium on charcoal paste catalyst

(5%w/w;lg). The mixture was shaken in a hydrogen atmosphere at 40 psig for 24 hours at the ambient temperature. . The catalyst was then filtered off and washed with ethyl acetate (100ml). The combined solutions were washed with water (2x20ml) and evaporated to dryness, to give 3α,4β-dihydroxy-6α- methoxy-2β-triphenylmethoxymethyltetrahydropyran

(2.8g), m.p. 134-138°C. [NMR:- s,1.59; d,1.63; d,1.66; q,2.10; d,2.41; d,2.71; s,3.30; m,3.37-3.45; m,3.57-3.63; d,4.46; d,4.78; m,7.20-7.35; m,7.45-7.50] .