Synthesis and biological activity of various derivatives of a novel class of potent, selective, and orally active prostaglandin D2 receptor antagonists. 1. Bicyclo[2.2.1]heptane derivatives.

Novel prostaglandin D(2) (PGD(2)) receptor antagonists were synthesized as a potential new class of antiallergic agents having a bicyclo[2.2.1]heptane ring system with sulfonamide groups. Some of them exhibit extremely potent antagonism of the PGD(2) receptor in radioligand binding and cAMP formation assays with IC(50) values below 50 nM and much less antagonism of TXA(2) and PGI(2) receptors. These potent PGD(2) receptor antagonists, when given orally, dramatically suppress various allergic inflammatory responses such as increased vascular permeability in allergic rhinitis, conjunctivitis, and asthma models. The excellent pharmacological profiles of PGD(2) receptor antagonists, originally synthesized in our laboratories, are of potentially great clinical significance. This study also provides experimental evidence suggesting that PGD(2) plays an important role in the pathogenesis of allergic diseases.

Synthesis and biological activity of various derivatives of a novel class of potent, selective, and orally active prostaglandin D2 receptor antagonists. 2. 6,6-Dimethylbicyclo[3.1.1]heptane derivatives.

In an earlier paper, we reported that novel prostaglandin D(2) (PGD(2)) receptor antagonists having the bicyclo[2.2.1]heptane ring system as a prostaglandin skeleton were a potent new class of antiallergic agents and suppressed various allergic inflammatory responses such as those observed in conjunctivitis and asthma models. In the present study, we synthesized PGD(2) receptor antagonists having the 6,6-dimethylbicyclo[3.1.1]heptane ring system. These derivatives have the amide moiety, in contrast to those with the bicyclo[2.2.1]heptane ring system, which have the sulfonamide group. The derivatives having the 6,6-dimethylbicyclo[3.1.1]heptane ring also exhibited strong activity in PGD(2) receptor binding and cAMP formation assays. In in vivo assays such as allergic rhinitis, conjunctivitis, and asthma models, these series of derivatives showed excellent pharmacological profiles. In particular, compound 45 also effectively suppressed eosinophil infiltration in allergic rhinitis and asthma models. This compound (45, S-5751) is now being developed as a promising alternative antiallergic drug candidate.

Synthesis and activities of oxidative metabolites of the anti-arthritic drug candidate S-2474.

We have synthesized and characterized some oxidative metabolites of S-2474. In this study, we discovered a novel skeleton, the 2,3-dihydrobenzofuran derivative, which inhibited PGE(2) production at a very low concentration and was effective in the anti-carrageenin footpad edema assay.

Short synthesis of tert-butyl-hydroxylated 3,5-di-tert-butyl-4-hydroxybenzaldehyde: Synthesis of tert-butyl-hydroxylated S-2474.

We have developed a very short synthesis of tert-butyl-hydroxylated di-tert-butyl-4-hydroxybenzaldehyde in which the HBr-DMSO system is used as an effective oxidant (overall yield of 45% for the entire four-step process from 2-tert-butyl-p-cresol). We also accomplished the synthesis of a major metabolite of the antiarthritic drug candidate S-2474.

Highly E-selective and effective synthesis of antiarthritic drug candidate S-2474 using quinone methide derivatives.

We have developed an efficient and E-selective synthesis of an antiarthritic drug candidate (E)-(5)-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2-ethyl-1,2-isothiazolidine-1,1-dioxide (S-2474; 1), in which alpha-methoxy-p-quinone methide is used as a key intermediate. alpha-Methoxy-p-quinone methide was revealed to be an equivalent to a p-hydroxy protected benzaldehyde. It reacts smoothly with alpha-sulfonyl carbanion to give 1,6-addition intermediates, which can be further processed to provide S-2474 directly in the presence of a base. This procedure gives S-2474 as an almost single isomer on the benzylidene double bond in excellent yield and thus is a very practical method adaptable to large-scale synthesis. The detailed mechanistic aspects are studied and discussed.

Total Synthesis of Terprenin, a Novel Immunosuppressive p-Terphenyl Derivative.

We achieved a total synthesis of terprenin, a novel potent immunoglobulin E antibody suppressant which was obtained from the fermentation broth of Aspergillus candidus RF-5672 and has a highly oxygenated p-terphenyl skeleton with a prenyloxy side chain. The key steps relied on the Suzuki reaction to construct the terphenyl skeleton and on regioselective halogenations to selectively combine the aromatic rings. The highly efficient and practical production of this important natural product offers promise for the development of a new type of antiallergic drug.

Total Synthesis of Terprenin, a Highly Potent and Novel Immunoglobulin E Antibody Suppressant.

Regioselective halogenations and Suzuki reactions ensure proper linkage of the aromatic rings in two total syntheses of terprenin (1). Both routes make it possible to prepare 1 efficiently and in large quantity.