On April 5, 2018, we entered into an operating lease agreement for 30,175 square feet of office space located in Boston, Massachusetts for our corporate headquarters. The lease commencement date was August 15, 2018 and we took occupancy in September 2018. We are leasing this space under a non-cancelable operating lease with an initial term of 123 months and an option to extend the lease for an additional five-year term. We did not include the extension option in our right-of-use asset and lease liability calculation as we do not consider it reasonably certain that we would exercise the option. Under the lease agreement, we received a three-month free rent period, which commenced on August 15, 2018, and a tenant improvement allowance of $3.6 million. We provided the lessor with a letter of credit to secure our obligations under the lease in the initial amount of $2.4 million, to be reduced to $1.8 million on the third anniversary of the rent commencement date and to $1.2 million on the fifth anniversary of the rent commencement date if we meet certain conditions set forth in the lease at each such date. The letter of credit amount is included in deposits and other assets on the accompanying condensed consolidated balance sheet.

On November 12, 2018, we entered into an operating lease agreement with Ionis to sublease 4,723 square feet of office space located in Carlsbad, California. The commencement date was March 2018 and the term of the lease is 64 months with a four-month free rent period. There is no extension option for this lease.

On May 8, 2019, we entered into an operating lease agreement for office space located in Dublin, Ireland. The lease commenced in May 2019 and the initial term of the lease is 18 months with an extension option. We have included a 12-month extension period in our right-of-use asset and lease liability calculation as we consider it reasonably certain that we will exercise the option to extend the lease for an additional 12 months.

The following table summarizes the contractual lease obligations as of March 31, 2020 (in thousands):

Years ended December 31,	Operating Leases
Remainder of 2020	$	1,877
2021		2,504
2022		2,403
2023		2,400
2024		2,395
Thereafter		9,565
Total minimum lease payments	$	21,144

Purchase commitments include agreements to purchase goods or services that are enforceable and legally binding on us and that specify all significant terms, including fixed or minimum quantities to be purchased, fixed, minimum or variable price provisions, and the approximate timing of the transaction. Such obligations are related principally to inventory purchase orders based on our current manufacturing needs and require significant lead times to be fulfilled by our vendors. Purchase commitments exclude agreements that are cancelable without penalty. As of March 31, 2020, our purchase commitments for the following 12 months were $0.9 million.