1,2-indandiols

Table 16.2-16. Microbial stereoselective oxidation of cis- and trans-1,2-indandiols 291.

Microorganisms degrading indane derivatives were screened for stereoselective oxidation of racemic cis- or trans-1,2-indandiol. Three promising strains specifically oxidizing the benzylic hydroxyl group were found (see Table 16.2-15). 

Fig. 1. Structure of indinavir sulfate. Shaded portion is cis-(lS)-amino-(2Jt)-indanol [(-)-CAI], and can be chemically synthesized from 1,2-indandiol of (2R) chirality...

The quest for microorganisms capable of performing the desired biotransformation of indene led to the isolation of several strains of the genus Rhodococcus from soil samples contaminated with aromatic compounds that are able to oxidize indene to 1,2-indandiols of different chirality, and various other oxygenated derivatives [8]. Induction studies indicated that several oxygenases were present and differentially induced by naphthalene, toluene, and indene. The stereospecific nature of the enzymes expressed in Rhodococcus as well as their abihty to tolerate indene as a substrate makes these microorganisms promising candidates for development as an industrial-scale biocatalyst for the production of (21 )-indandiol. 

Rhodococcus sp. 124 was isolated fi-om a toluene-contaminated aquifer and was found to oxidize indene to 1,2-indandiol and several other products. The undesired products 1-indenol and 1-indanone were formed directly from indene while racemic l-keto-2-hydroxy-indan was formed from the indandiols. Based on product formation profiles and induction experiments, 124 was hypothesized... 

Obviously with the indan-l,2-diol substrates there is no symmetrical meso intermediate which makes interpretation of the mechanism more difficult. In both the cyclohexan-l,2-diol and the indan-l,2-diol series the trans diols react faster and cis diols (both enantiomers for indandiol) are seen as intermediates. The (IS,2R) cis indandiol 29 is faster reacting and on incubation of the racemate only a very small trace of the R,R)-trans 28 isomer is observed. 2-Hydroxyin-dan-1 -one 30, an observed intermediate in these biotransformations, undergoes kinetic resolution when incubated as a racemic substrate. The faster reacting enantiomer is reduced to the faster reacting cis (lS,2i )-indan-l,2-diol 29 which is subsequently transformed into both trans diols and ultimately the (S,S)-iso-mer. Current work is focussing on determining the absolute configuration of the intermediate a-hydroxyketone 30. 

Naphthalene dioxygenase carried out dioxygenation of indene to ris-(l R,2S)-indandiol, monooxygenation to lS-indenol, and in addition dehydrogenation of indan to indene. Further details of this and other reactions of indanol are given in Chapter 6, Section 6.2.3. 

Indan oxide hydrolysis rate constant to cis-(IS,2i )-indandiol... 

C]-Metabolite concentration czs-(lS,2R)-Indandiol excretion rate czs-(lR,2S)-Indandiol excretion rate Indene uptake rate Indan oxide excretion rate l-Keto-2-hydroxy-indan excretion rate frans-(lR,2R)-Indandiol excretion rate [ -fra s-( lR,2R)-Indandiol concentration Indan oxide hydrolysis flux to czs-(lS,2R)-indandiol Dioxygenase flux Flux for enzyme i... 

Indan oxide hydrolysis flux to fraMS-(lR,2R)-indandiol... 

Protease inhibitors are well-characterized chiral drugs in terms of their mechanism of action. An important new class of protease inhibitors comprises molecules designed to treat HIV infection. In particular, indinavir sulfate (CRIXIVAN, Merck and Co., Inc.) contains five chiral centers that must be of a specific orientation for the molecule to have the desired therapeutic effect. Manufacturing processes for these compounds involving chemical synthesis steps can be quite inefficient, due to yield reduction caused by racemization at each step where a chiral center is formed. A key intermediate in the synthesis of CRIXIVAN is cis-(lS,2R)-l-amino-2-indanol [(-)-CAI], an indene derivative that contributes two chiral centers to indinavir sulfate (Fig. 1). To circumvent the technically demanding chemical synthesis of (-)-CAI and reduce product loss, Merck scientists conceptualized a bioconversion process in which indene is oxidized to one of three derivatives that can serve as precursors to (-)-CAI cis-(lS,2R)-indandiol, trans-(lR,2R)-indandiol, or (lS,2R)-indan oxide. Oxygenases that have been identified in isolates of the genus Pseudomonas and Rhodococcus can catalyze this transformation. 

A number of oxygenases have been described to catalyze multiple transformations of indene. Toluene dioxygenase (TDO) has been found to possess both monooxygenase and dioxygenase activities. Wackett and co-workers induced Pseudomonas putida F39/D with toluene, which then converted indene to cis-(lS,2R)-indandiol in approximately 30% e.e. and (IS)-indenol in 26% e.e. [5]. Gibson et al. found in Pseudomonas sp. 9816-4 that indene serves as a substrate... 

Fig. 2. Indene bioconversion network in Rhodococcus strain 124 proposed by Chartrain et al. [8]. Indene is converted to the indandiol enantiomers shown through specific oxygenase activities. Dioxygenases produce the cis enantiomers of indandiol while the monooxygenase converts indene to indan oxide. The indandiols are then converted to l-keto-2-hydroxy-indan through the action of dehydrogenase enzymes and a proposed undetectable 1,2-indenediol intermediate...

C]-czs-(lS,2i )-Indandiol was used to measure directly the corresponding steady state dehydrogenase flux, Vrdh> in the KYI indene bioconversion network. By measuring the formation of [ C]-l-keto-2-hydroxy-indan associated with the concomitant depletion of [ C]-czs-(lS,2i )-indandiol in steady state cells, the... 

---