TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation: No preparation method is given. Preferred Components: The PKS is a hybrid PKS comprising modules, domains, and/or their portions from at least two PKSs. The PKS comprises a loading module capable of using isobutyryl coenzyme A (CoA) or pivaloyl-CoA as a starter unit, and a module capable of extending using 2-methylmalonyl-CoA as an extending unit. The trimethylpentanoic acid is 2,2,4-trimethylpentanoic acid, and the PKS comprises a loading module capable of using isobutyryl-CoA as a starter unit, where the loading module comprises: acyltransferase(L) (AT(L)) and acyl carrier protein(L) ((ACP(L)) of avermectin (Ave) load-mod1 and the module capable of extending using 2-methylmalonyl-CoA as an extending unit comprises ketosynthase (KS) and mm-acyltransferase (mm-AT) of Ave load-mod1, dehydratase (DH), enoyl reductase and ketoreductase (KR) of erythromycin mod4 or nanchangmycin mod2, a cMT domain, acyl carrier protein or TE; or AT(L), ACP(L) and KS-1 of Lipomycin load module, where the module capable of extending using 2-methylmalonyl-CoA as an extending unit comprises the modules mm-AT, DH, enoyl reductase, KR, cMT, and acyl carrier protein. The PKS comprises a loading module capable of using pivaloyl-CoA as a starter unit, where the loading module comprises: AT(L) and ACP(L) of Ave Load-mod1 and the module capable of extending using 2-methylmalonyl-CoA as an extending unit comprises KS and mm-AT of Ave load-mod1, and DH, enoyl reductase, KR, acyl carrier protein and TE of erythromycin mod4-TE or nanchangmycin mod2-TE; or AT(L), ACP(L) and KS-1 of But load module of Streptomyces rochei, where the module capable of extending using 2-methylmalonyl-CoA as an extending unit comprises mm-AT of Ave load-mod1, and DH, enoyl reductase, KR, acyl carrier protein of erythromycin mod4. The isobutyryl-CoA starter unit comprises AT(L), ACP(L) and KS-1 of Ave load-mod1, and a cMT domain between the AT(L) and ACP(L) domains, where the module capable of extending using 2-methylmalonyl-CoA as an extending unit comprises mm-AT of Ave load-mod1, and DH, enoyl reductase, KR, acyl carrier protein of erythromycin mod4. The replicon is a plasmid or vector, where the vector is an expression vector. The host cell further comprises: IveE, PdhD, BfmBB, BfmBAA, BfmBAB or their functional variants; PrpE and PccA/AccB or their functional variants; and malonyl-CoA-reductase, malonate semialdehyde reductase, 3-hydroxypropionyl-CoA synthase, 3-hydroxypropionyl-CoA dehydratase, and acryloyl-CoA reductase or their functional variants. Preferred Method: The host cell when cultured produces the trimethylpentanoic acid. The method further comprises: isolating the trimethylpentanoic acid; and reducing the trimethylpentanoic acid to produce a trimethylpentanol or an isooctane. EXAMPLE - No suitable example given.