Ethyl naphthoates a h were successfully reduced
Ethyl 1-naphthoates (10a–h) were successfully reduced to 1-naphthylmethanols (12a–h) by using LiAlH4 with 8–87% yields. Then PCC was used to convert the alcohols into the corresponding 4-alkyl-1-naphthaldehyde derivatives (13a–h) with relatively higher yields (58–90%) as represented in Scheme 2. Then, a well-known three step synthesis was used to complete the syntheses. Simply, addition of allylmagnesium bromide over 1-naphthaldehydes (13a–h) and commercially available 4-methyl-1-naphthaldehyde (13i) yielded homoallylic alcohols (14a–i) in 54–91% yields. Acrylation with acryloyl chloride in the presence of triethylamine followed by ring closing metathesis reactions gave the final klavuzon derivatives (3 and 16a–h, Scheme 2). Another important klavuzon derivative 20 was also prepared by the same three step synthesis starting from commercially available 1,2,3,4-tetrahydrophenanthrene-9-carbaldehyde (17) as represented in Scheme 3. Alternatively, 5,6-dihydro-2H-pyran-2-one pharmacophore can be prepared from the isomerization of 3,6-dihydro-2H-pyran 2-one in the presence of an amine base. A similar isomerization can also be observed for naphthalen-1-yl substituted 3,6-dihydro-2H-pyran 2-one derivatives inside the cells to give the corresponding klavuzons, so derivatives of 3,6-dihydro-2H-pyran 2-one may have therapeutic importance. For these reasons, a list of 4-alkylnaphthalen-1-yl substituted 3,6-dihydro-2H-pyran 2-one derivatives (23a–e) were also prepared starting from 4-methyl-1-naphthoic pitavastatin (Scheme 4). Compounds 13a–h were synthesized by the same synthetic route reported above and then reacted with vinylmagnesium bromide to give allylic alcohols 21a–e with 67–87% yields. Steglich esterification of the formed alcohols with but-3-enoic acid gave esters 22a–e. Finally, ring closing metathesis reactions of the esters 22a–e yielded 4-alkylnaphthalen-1-yl substituted 3,6-dihydro-2H-pyran 2-one derivatives (23a–e). Although, compounds 23a–e were isolated and characterized successfully, it was noted that these compounds totally decomposed even at +4°C in three months. Decomposition of 6-(4-methylnaphthalen-1-yl)-3,6-dihydro-2H-pyran 2-one (23a). was also shown by 1H NMR spectroscopy in Fig. 2. Observed instability of the 4-alkylnaphthalen-1-yl substituted 3,6-dihydro-2H-pyran 2-one derivatives led us to convert compound 23b–e to the corresponding klavuzon derivatives 16b–e by isomerization with DBU, instead of testing them to determine their antiproliferative properties (Fig. 3). Antiproliferative properties of all prepared klavuzon derivatives (3, 16a–h and 20) were tested in healthy (HPDEC) and cancerous (MIA PaCa-2) pancreatic cell lines by MTT cell viability assay. Camptothecin (CPT) was used as positive control. There were differences between the cell culture conditions of both cell lines, and the most important difference was that HPDEC should be cultured (and tested) over type I collagen coated surface. Because there is a Michael acceptor in the structure of klavuzon, a small amount of the tested compounds can bind to the collagen and actual level of cytotoxicity may not be observed. To determine the effect of the collagen in MTT assay, three klavuzon derivatives (3, 16b and 16c) were also tested in MIA PaCa-2 cell lines which are cultured in type I collagen coated 96 well microplate. All IC50 values calculated for klavuzon derivatives were summarized in Table 1. According to these data, collagen coating did not have any influence in structure activity relationship of klavuzon derivatives. It slightly increased the IC50 values for compounds 3 and 16c. It might be possible that MIA PaCa-2 cell viability and resistance to goniothalamin increases in the presence of type I collagen or a small amount of klavuzons was bound to the collagen as expected. On the other hand, effect of collagen over the IC50 value of compound 16b was more dramatic. It is difficult to announce the reason for this difference between the IC50 values of compounds 16b and 16c. In one thought, this difference may not be the result of interactions between klavuzon and collagen because if that is the case compounds 16b should have similar IC50 values for HPDEC and MIA PaCa-2 cell lines cultured over collagen. Only explanation can be the development of a resistance in MIA PaCa-2 cells when they grow over collagen. Overall, it can be concluded that SAR of klavuzon derivatives was not affected by collagen coating (Table 1).